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/***********************************************************************************/
/*  Copyright 2009 WSL Institute for Snow and Avalanche Research    SLF-DAVOS      */
/***********************************************************************************/
/* This file is part of MeteoIO.
    MeteoIO is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    MeteoIO is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with MeteoIO.  If not, see <http://www.gnu.org/licenses/>.
*/
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#include <cmath>
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#include <limits.h>
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#include <meteoio/DEMObject.h>
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#include <meteoio/MathOptim.h>
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#include <meteoio/meteolaws/Meteoconst.h> //for math constants
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/**
* @file DEMObject.cc
* @brief implementation of the DEMBoject class
*/

using namespace std;

namespace mio {
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const double dbl_max = std::numeric_limits<double>::max();
const double dbl_min = -std::numeric_limits<double>::max();
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/**
* @brief Default constructor.
* Initializes all variables to 0, except lat/long which are initialized to IOUtils::nodata
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* @param i_algorithm specify the default algorithm to use for slope computation (default=DFLT)
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*/
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DEMObject::DEMObject(const slope_type& i_algorithm)
           : Grid2DObject(), slope(), azi(), curvature(), Nx(), Ny(), Nz(),
             min_altitude(dbl_max), min_slope(dbl_max), min_curvature(dbl_max),
             max_altitude(dbl_min), max_slope(dbl_min), max_curvature(dbl_min),
             CalculateSlope(&DEMObject::CalculateCorripio),
             update_flag(INT_MAX), dflt_algorithm(i_algorithm),
             slope_failures(0), curvature_failures(0)
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{
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	setDefaultAlgorithm(i_algorithm);
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}

/**
* @brief Constructor that sets variables.
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* @param i_ncols number of colums in the grid2D
* @param i_nrows number of rows in the grid2D
* @param i_cellsize value for cellsize in grid2D
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* @param i_llcorner lower lower corner point
* @param i_algorithm specify the default algorithm to use for slope computation (default=DFLT)
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*/
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DEMObject::DEMObject(const size_t& i_ncols, const size_t& i_nrows,
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                     const double& i_cellsize, const Coords& i_llcorner, const slope_type& i_algorithm)
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           : Grid2DObject(i_ncols, i_nrows, i_cellsize, i_llcorner),
             slope(), azi(), curvature(), Nx(), Ny(), Nz(),
             min_altitude(dbl_max), min_slope(dbl_max), min_curvature(dbl_max),
             max_altitude(dbl_min), max_slope(dbl_min), max_curvature(dbl_min),
             CalculateSlope(&DEMObject::CalculateCorripio),
             update_flag(INT_MAX), dflt_algorithm(i_algorithm),
             slope_failures(0), curvature_failures(0)
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{
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	setDefaultAlgorithm(i_algorithm);
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}

/**
* @brief Constructor that sets variables.
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* @param i_ncols number of colums in the grid2D
* @param i_nrows number of rows in the grid2D
* @param i_cellsize value for cellsize in grid2D
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* @param i_llcorner lower lower corner point
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* @param i_altitude grid2D of elevations
* @param i_update also update slope/normals/curvatures and their min/max? (default=true)
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* @param i_algorithm specify the default algorithm to use for slope computation (default=DFLT)
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*/
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DEMObject::DEMObject(const size_t& i_ncols, const size_t& i_nrows,
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                     const double& i_cellsize, const Coords& i_llcorner, const Array2D<double>& i_altitude,
                     const bool& i_update, const slope_type& i_algorithm)
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           : Grid2DObject(i_ncols, i_nrows, i_cellsize, i_llcorner, i_altitude),
             slope(), azi(), curvature(), Nx(), Ny(), Nz(),
             min_altitude(dbl_max), min_slope(dbl_max), min_curvature(dbl_max),
             max_altitude(dbl_min), max_slope(dbl_min), max_curvature(dbl_min),
             CalculateSlope(&DEMObject::CalculateCorripio),
             update_flag(INT_MAX), dflt_algorithm(i_algorithm),
             slope_failures(0), curvature_failures(0)
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{
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	setDefaultAlgorithm(i_algorithm);
	if(i_update==false) {
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		updateAllMinMax();
	} else {
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		update(i_algorithm);
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	}
}

/**
* @brief Constructor that sets variables from a Grid2DObject
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* @param i_dem grid contained in a Grid2DObject
* @param i_update also update slope/normals/curvatures and their min/max? (default=true)
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* @param i_algorithm specify the default algorithm to use for slope computation (default=DFLT)
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*/
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DEMObject::DEMObject(const Grid2DObject& i_dem, const bool& i_update, const slope_type& i_algorithm)
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           : Grid2DObject(i_dem.ncols, i_dem.nrows, i_dem.cellsize, i_dem.llcorner, i_dem.grid2D),
             slope(), azi(), curvature(), Nx(), Ny(), Nz(),
             min_altitude(dbl_max), min_slope(dbl_max), min_curvature(dbl_max),
             max_altitude(dbl_min), max_slope(dbl_min), max_curvature(dbl_min),
             CalculateSlope(&DEMObject::CalculateCorripio),
             update_flag(INT_MAX), dflt_algorithm(i_algorithm),
             slope_failures(0), curvature_failures(0)
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{
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	setDefaultAlgorithm(i_algorithm);
	if(i_update==false) {
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		updateAllMinMax();
	} else {
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		update(i_algorithm);
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	}
}

/**
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* @brief Constructor that sets variables from a subset of another DEMObject,
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* given an origin (X,Y) (first index being 0) and a number of columns and rows
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* @param i_dem dem contained in a DEMDObject
* @param i_nx X coordinate of the new origin
* @param i_ny Y coordinate of the new origin
* @param i_ncols number of columns for the subset dem
* @param i_nrows number of rows for the subset dem
* @param i_update also update slope/normals/curvatures and their min/max? (default=true)
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* @param i_algorithm specify the default algorithm to use for slope computation (default=DFLT)
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*/
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DEMObject::DEMObject(const DEMObject& i_dem, const size_t& i_nx, const size_t& i_ny,
                     const size_t& i_ncols, const size_t& i_nrows,
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                     const bool& i_update, const slope_type& i_algorithm)
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           : Grid2DObject(i_dem, i_nx,i_ny, i_ncols,i_nrows),
             slope(), azi(), curvature(), Nx(), Ny(), Nz(),
             min_altitude(dbl_max), min_slope(dbl_max), min_curvature(dbl_max),
             max_altitude(dbl_min), max_slope(dbl_min), max_curvature(dbl_min),
             CalculateSlope(&DEMObject::CalculateCorripio),
             update_flag(i_dem.update_flag), dflt_algorithm(i_algorithm),
             slope_failures(0), curvature_failures(0)
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{
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	if ((i_ncols==0) || (i_nrows==0)) {
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		throw InvalidArgumentException("requesting a subset of 0 columns or rows for DEMObject", AT);
	}
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	//handling of the update properties
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	setDefaultAlgorithm(i_algorithm);
	if(i_update==true) {
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		//if the object is in automatic update, then we only process the arrays according to
		//the update_flag
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		update(i_algorithm);
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	} else {
		//if the object is NOT in automatic update, we manually copy all non-empty arrays
		//from the original set
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		size_t nx, ny;
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		i_dem.slope.size(nx, ny);
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		if(nx>0 && ny>0) {
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			slope.subset(i_dem.slope,i_nx,i_ny, i_ncols,i_nrows);
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		}
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		i_dem.azi.size(nx, ny);
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		if(nx>0 && ny>0) {
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			azi.subset(i_dem.azi,i_nx,i_ny, i_ncols,i_nrows);
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		}
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		i_dem.curvature.size(nx, ny);
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		if(nx>0 && ny>0) {
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			curvature.subset(i_dem.curvature,i_nx,i_ny, i_ncols,i_nrows);
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		}
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		i_dem.Nx.size(nx, ny);
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		if(nx>0 && ny>0) {
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			Nx.subset(i_dem.Nx,i_nx,i_ny, i_ncols,i_nrows);
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		}
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		i_dem.Ny.size(nx, ny);
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		if(nx>0 && ny>0) {
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			Ny.subset(i_dem.Ny,i_nx,i_ny, i_ncols,i_nrows);
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		}
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		i_dem.Nz.size(nx, ny);
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		if(nx>0 && ny>0) {
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			Nz.subset(i_dem.Nz,i_nx,i_ny, i_ncols,i_nrows);
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		}

		updateAllMinMax();
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	}
}

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/**
* @brief Set the properties that will be calculated by the object when updating
* The following properties can be turned on/off: slope/azimuth and/or normals, and/or curvatures.
* Flags are combined using the binary "|" operator.
* @param in_update_flag parameters to update
*/
void DEMObject::setUpdatePpt(const update_type& in_update_flag) {
	update_flag = in_update_flag;
}

/**
* @brief Get the properties that will be calculated by the object when updating
* @return combination of flags set with the binary "|" operator
*/
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int DEMObject::getUpdatePpt() const {
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	return update_flag;
}

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/**
* @brief Force the computation of the local slope, azimuth, normal vector and curvature.
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* It has to be called manually since it can require some time to compute. Without this call,
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* the above mentionned parameters are NOT up to date.
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* @param algorithm algorithm to use for computing slope, azimuth and normals
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*/
void DEMObject::update(const slope_type& algorithm) {
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//This method recomputes the attributes that are not read as parameters
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//(such as slope, azimuth, normal vector)

	// Creating tables
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	if(update_flag&SLOPE) {
		slope.resize(ncols, nrows);
		azi.resize(ncols, nrows);
	}
	if(update_flag&CURVATURE) {
		curvature.resize(ncols, nrows);
	}
	if(update_flag&NORMAL) {
		Nx.resize(ncols, nrows);
		Ny.resize(ncols, nrows);
		Nz.resize(ncols, nrows);
	}
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	CalculateAziSlopeCurve(algorithm);
	updateAllMinMax();
}

/**
* @brief Force the computation of the local slope, azimuth, normal vector and curvature.
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* It has to be called manually since it can require some time to compute. Without this call,
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* the above mentionned parameters are NOT up to date.
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* @param algorithm algorithm to use for computing slope, azimuth and normals
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* it is either:
* - HICK that uses the maximum downhill slope method (Dunn and Hickey, 1998)
* - FLEMING uses a 4 neighbors algorithm (Fleming and Hoffer, 1979)
* - CORRIPIO that uses the surface normal vector using the two triangle method given in Corripio (2002)
* and the eight-neighbor algorithm of Horn (1981) for border cells.
* - D8 uses CORRIPIO but discretizes the resulting azimuth to 8 cardinal directions and the slope is rounded to the nearest degree. Curvature and normals are left untouched.
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*
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* The azimuth is always computed using the Hodgson (1998) algorithm.
*/
void DEMObject::update(const std::string& algorithm) {
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//This method recomputes the attributes that are not read as parameters
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//(such as slope, azimuth, normal vector)
	slope_type type;

	if(algorithm.compare("HICK")==0) {
		type=HICK;
	} else if(algorithm.compare("FLEMING")==0) {
		type=FLEM;
	} else if(algorithm.compare("HORN")==0) {
		type=HORN;
	} else if(algorithm.compare("CORRIPIO")==0) {
		type=CORR;
	} else if(algorithm.compare("D8")==0) {
		type=D8;
	} else if(algorithm.compare("DEFAULT")==0) {
		type=DFLT;
	} else {
		throw InvalidArgumentException("Chosen slope algorithm " + algorithm + " not available", AT);
	}
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	update(type);
}

/**
* @brief Sets the default slope calculation algorithm
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* @param i_algorithm specify the default algorithm to use for slope computation
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*/
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void DEMObject::setDefaultAlgorithm(const slope_type& i_algorithm) {
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//This method MUST be called by each constructor!
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	if(i_algorithm==DFLT) {
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		dflt_algorithm = CORR;
	} else {
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		dflt_algorithm = i_algorithm;
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	}
}

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/**
* @brief Get the default slope calculation algorithm
* @return default algorithm to use for slope computation
*/
int DEMObject::getDefaultAlgorithm() const {
	return dflt_algorithm;
}
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/**
* @brief Recomputes the min/max of altitude, slope and curvature
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* It return +/- std::numeric_limits\<double\>\:\:max() for a given parameter if its grid was empty/undefined
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*/
void DEMObject::updateAllMinMax() {
//updates the min/max parameters of all 2D tables
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	if(update_flag&SLOPE) {
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		min_slope = slope.getMin();
		max_slope = slope.getMax();
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	}
	if(update_flag&CURVATURE) {
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		min_curvature = curvature.getMin();
		max_curvature = curvature.getMax();
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	}

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	min_altitude = grid2D.getMin();
	max_altitude = grid2D.getMax();
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}

/**
* @brief Prints the list of points that have an elevation different than nodata but no slope or curvature
* Such points can happen if they are surrounded by too many points whose elevation is nodata
* If no such points exist, it prints nothing.
*/
void DEMObject::printFailures() {
	bool header=true;

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	if(update_flag&SLOPE) {
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		for ( size_t j = 0; j < nrows; j++ ) {
			for ( size_t i = 0; i < ncols; i++ ) {
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				if((slope(i,j)==IOUtils::nodata) && (grid2D(i,j)!=IOUtils::nodata)) {
					if(header==true) {
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						cerr << "[i] DEM slope could not be computed at the following points \n";
						cerr << "[i]\tGrid Point\tElevation\tSlope\n";
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						header=false;
					}
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					cerr << "[i]\t(" << i << "," << j << ")" << "\t\t" << grid2D(i,j) << "\t\t" << slope(i,j) << "\n";
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				}
			}
		}
	}

	if(update_flag&CURVATURE) {
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		for ( size_t j = 0; j < nrows; j++ ) {
			for ( size_t i = 0; i < ncols; i++ ) {
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				if((curvature(i,j)==IOUtils::nodata) && (grid2D(i,j)!=IOUtils::nodata)) {
					if(header==true) {
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						cerr << "[i] DEM curvature could not be computed at the following points \n";
						cerr << "[i]\tGrid Point\tElevation\tCurvature\n";
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						header=false;
					}
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					cerr << "[i]\t(" << i << "," << j << ")" << "\t\t" << grid2D(i,j) << "\t\t" <<  curvature(i,j) << "\n";
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				}
			}
		}
	}
	if(header==false) {
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		cerr << std::endl;
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	}
}

/**
* @brief Clean up the DEM Object
* When computing the slope and curvature, it is possible to get points where the elevation is known
* but where no slope/azimuth/normals/curvature could be computed. This method sets the elevation to nodata for such points,
* so that latter use of the DEM would be simpler (simply test the elevation in order to know if the point can be used
* and it guarantees that all other informations are available).If the slope/azimuth/normals/curvature tables were manually updated, this method will NOT perform any work (it requires the count of slopes/curvature failures to be greater than zero)
*
* IMPORTANT: calling this method DOES change the table of elevations!
*/
void DEMObject::sanitize() {
	if(slope_failures>0 || curvature_failures>0) {
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		for ( size_t j = 0; j < nrows; j++ ) {
			for ( size_t i = 0; i < ncols; i++ ) {
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				if(update_flag&SLOPE) {
					if((slope(i,j)==IOUtils::nodata) && (grid2D(i,j)!=IOUtils::nodata)) {
						grid2D(i,j) = IOUtils::nodata;
					}
				}
				if(update_flag&CURVATURE) {
					if((curvature(i,j)==IOUtils::nodata) && (grid2D(i,j)!=IOUtils::nodata)) {
						grid2D(i,j) = IOUtils::nodata;
					}
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				}
			}
		}
	}
}

/**
* @brief Computes the horizontal distance between two points in a metric grid
* @param xcoord1 east coordinate of the first point
* @param ycoord1 north coordinate of the first point
* @param xcoord2 east coordinate of the second point
* @param ycoord2 north coordinate of the second point
* @return horizontal distance in meters
*
*/
double DEMObject::horizontalDistance(const double& xcoord1, const double& ycoord1, const double& xcoord2, const double& ycoord2)
{
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	return sqrt( Optim::pow2(xcoord2-xcoord1) + Optim::pow2(ycoord2-ycoord1) );
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}

/**
* @brief Computes the horizontal distance between two points in a metric grid
* @param point1 first point (ie: origin)
* @param point2 second point (ie: destination)
* @return horizontal distance in meters
*
*/
double DEMObject::horizontalDistance(Coords point1, const Coords& point2)
{
	if(point1.isSameProj(point2)==false) {
		point1.copyProj(point2);
	}
	return horizontalDistance(point1.getEasting(), point1.getNorthing(),
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	                          point2.getEasting(), point2.getNorthing() );
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}


/**
* @brief Returns the distance *following the terrain* between two coordinates
* @param point1 first point (ie: origin)
* @param point2 second point (ie: destination)
* @return distance following the terrain in meters
*
*/
double DEMObject::terrainDistance(Coords point1, const Coords& point2) {
	std::vector<GRID_POINT_2D> vec_points;
	double distance=0.;
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	size_t last_point=0; //point 0 is always the starting point
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	//Checking that both points use the same projection is done in getPointsBetween()
	getPointsBetween(point1, point2, vec_points);
	if(vec_points.size()<=1) {
		return 0.;
	}

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	for(size_t ii=1; ii<vec_points.size(); ii++) {
		const size_t ix1=vec_points[last_point].ix;
		const size_t iy1=vec_points[last_point].iy;
		const size_t ix2=vec_points[ii].ix;
		const size_t iy2=vec_points[ii].iy;
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		if(grid2D(ix2,iy2)!=IOUtils::nodata) {
			if(grid2D(ix1,iy1)!=IOUtils::nodata) {
				//distance += sqrt( pow2((ix2-ix1)*cellsize) + pow2((iy2-iy1)*cellsize) + pow2(grid2D(ix2,iy2)-grid2D(ix1,iy1)) );
				const double z1=grid2D(ix1,iy1);
				const double z2=grid2D(ix2,iy2);
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				const double tmpx=Optim::pow2((double)(ix2-ix1)*cellsize);
				const double tmpy=Optim::pow2((double)(iy2-iy1)*cellsize);
				const double tmpz=Optim::pow2(z2-z1);
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				distance += sqrt( tmpx + tmpy + tmpz );
			}
			last_point = ii;
		}
	}

	return distance;
}

/**
* @brief Returns a list of grid points that are on the straight line between two coordinates
* @param point1 first point (ie: origin)
* @param point2 second point (ie: destination)
* @param vec_points vector of points that are in between
*
*/
void DEMObject::getPointsBetween(Coords point1, Coords point2, std::vector<GRID_POINT_2D>& vec_points) {

	if(point1.isSameProj(point2)==false) {
		point1.copyProj(point2);
	}

	if(point1.getEasting() > point2.getEasting()) {
		//we want xcoord1<xcoord2, so we swap the two points
		const Coords tmp = point1;
		point1 = point2;
		point2 = tmp;
	}

	//extension of the line segment (pts1, pts2) along the X axis
	const int ix1 = (int)floor( (point1.getEasting() - llcorner.getEasting())/cellsize );
	const int iy1 = (int)floor( (point1.getNorthing() - llcorner.getNorthing())/cellsize );
	const int ix2 = (int)floor( (point2.getEasting() - llcorner.getEasting())/cellsize );
	const int iy2 = (int)floor( (point2.getNorthing() - llcorner.getNorthing())/cellsize );

	if(ix1==ix2) {
		//special case of vertical alignement
		for(int iy=MIN(iy1,iy2); iy<=MAX(iy1,iy2); iy++) {
			GRID_POINT_2D pts;
			pts.ix = ix1;
			pts.iy = iy;
			vec_points.push_back(pts);
		}
	} else {
		//normal case
		//equation of the line between the two points
		const double a = ((double)(iy2-iy1)) / ((double)(ix2-ix1));
		const double b = (double)iy1 - a * (double)ix1;

		for(int ix=ix1; ix<=ix2; ix++) {
			//extension of the line segment (ix, ix+1) along the Y axis
			int y1 = (int)floor( a*(double)ix+b );
			//const int y2 = MIN( (int)floor( a*((double)ix+1)+b ) , iy2);
			int y2 = (int)floor( a*((double)ix+1)+b );
			if(ix==ix2 && y1==iy2) {
				//we don't want to overshoot when reaching the target cell
				y2 = y1;
			}

			if(y1>y2) {
				//we want y1<y2, so we swap the two coordinates
				const int ytemp=y1;
				y1=y2; y2=ytemp;
			}

			for(int iy=y1; iy<=y2; iy++) {
				GRID_POINT_2D pts;
				pts.ix = ix;
				pts.iy = iy;
				//make sure we only return points within the dem
				if(ix>0 && ix<(signed)ncols && iy>0 && iy<(signed)nrows) {
					vec_points.push_back(pts);
				}
			}
		}
	}
}

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/**
* @brief Returns a list of grid points that are on the straight line between two coordinates
* @param point the origin point
* @param bearing direction given by a compass bearing
* @param vec_points vector of points that are between point and the edge of the dem following direction given by bearing
*
*/
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void DEMObject::getPointsBetween(const Coords& point, const double& bearing, std::vector<GRID_POINT_2D>& vec_points) {
	//equation of the line between for a point (x0,y0) and a bearing
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	const double x0 = (point.getEasting() - llcorner.getEasting())/cellsize;
	const double y0 = (point.getNorthing() - llcorner.getNorthing())/cellsize;
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	const double bear=fmod(bearing+360., 360.); //this should not be needed, but as safety...
	const double a = tan( IOUtils::bearing_to_angle(bear) ); //to get trigonometric angle
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	const double b = y0 - a * x0;
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	//looking which point is on the limit of the grid and not outside
	Coords pointlim;
	pointlim.copyProj(llcorner); //we use the same projection parameters as the DEM
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	//define the boundaries according to the quadrant we are in
	double xlim, ylim;
	if(bear>=0. && bear<90.) {
		xlim = (double)(ncols-1);
		ylim = (double)(nrows-1);
	} else if (bear>=90. && bear<180.) {
		xlim = (double)(ncols-1);
		ylim = 0.;
	} else if (bear>=180. && bear<270.) {
		xlim = 0.;
		ylim = 0.;
	} else {
		xlim = 0.;
		ylim = (double)(nrows-1);
	}

	//calculate the two possible intersections between the bearing line and the boundaries
	const double y2 = a * xlim + b;
	const double x2 = (ylim - b) / (a + 1e-12);

	//Find out which point is the first intersect and take it as our destination point
	if(bear>=90. && bear<270.) {
		if (y2 >= ylim)
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        		pointlim.setXY((xlim*cellsize)+llcorner.getEasting(),(y2*cellsize)+llcorner.getNorthing() , IOUtils::nodata);
		else
        		pointlim.setXY((x2*cellsize)+llcorner.getEasting(),(ylim*cellsize)+llcorner.getNorthing() , IOUtils::nodata);
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	} else {
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		if (y2 <= ylim)
        		pointlim.setXY((xlim*cellsize)+llcorner.getEasting(),(y2*cellsize)+llcorner.getNorthing() , IOUtils::nodata);
		else
        		pointlim.setXY((x2*cellsize)+llcorner.getEasting(),(ylim*cellsize)+llcorner.getNorthing() , IOUtils::nodata);
	}
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	if(gridify(pointlim)==false) {
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		std::stringstream tmp;
		tmp << "[E] Wrong destination point calculated for bearing " << bearing;
		throw InvalidArgumentException(tmp.str(), AT);
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	}

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	getPointsBetween(point, pointlim, vec_points);
	//HACK BUG : for bearing=160 -> both start and end points are missing from the list!!
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}

/**
* @brief Returns the horizon from a given point looking toward a given bearing
* @param point the origin point
* @param bearing direction given by a compass bearing
* @return angle above the horizontal (in deg)
*
*/
double DEMObject::getHorizon(const Coords& point, const double& bearing) {

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	std::vector<Grid2DObject::GRID_POINT_2D> vec_points;
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	getPointsBetween(point, bearing, vec_points);

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	//Starting point
	const int ix0 = (int)point.getGridI();
	const int iy0 = (int)point.getGridJ();
	const double height0 = grid2D(ix0,iy0);
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	//going through every point and looking for the highest tangent (which is also the highest angle)
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	double max_tangent = 0.;
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	for (size_t ii=0; ii < vec_points.size(); ii++) {
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		const int ix = (int)vec_points[ii].ix;
		const int iy = (int)vec_points[ii].iy;
		const double delta_height = grid2D(ix, iy) - height0;
		const double x_distance = (double)(ix - ix0) * cellsize;
		const double y_distance = (double)(iy - iy0) * cellsize;
		const double distance = sqrt(x_distance * x_distance + y_distance * y_distance);
		const double tangent = (delta_height / distance);

		if(tangent > max_tangent) max_tangent = tangent;
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	}

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	//returning the angle matching the highest tangent
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	return ( atan(max_tangent)*Cst::to_deg );
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}

/**
* @brief Returns the horizon from a given point looking 360 degrees around by increments
* @param point the origin point
* @param increment to the bearing between two angles
* @param horizon vector of heights above a given angle
*
*/
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void DEMObject::getHorizon(const Coords& point, const double& increment, std::vector<double>& horizon)
{
	for(double bearing=0.0; bearing <360.; bearing += increment) {
		const double alpha = getHorizon(point, bearing * Cst::PI/180.);
		horizon.push_back(alpha);
	}
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}

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void DEMObject::CalculateAziSlopeCurve(slope_type algorithm) {
//This computes the slope and the aspect at a given cell as well as the x and y components of the normal vector
	double A[4][4]; //table to store neigbouring heights: 3x3 matrix but we want to start at [1][1]
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	                //we use matrix notation: A[y][x]
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	if(algorithm==DFLT) {
		algorithm = dflt_algorithm;
	}

	slope_failures = curvature_failures = 0;
	if(algorithm==HICK) {
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		CalculateSlope = &DEMObject::CalculateHick;
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	} else if(algorithm==HORN) {
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		CalculateSlope = &DEMObject::CalculateHorn;
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	} else if(algorithm==CORR) {
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		CalculateSlope = &DEMObject::CalculateCorripio;
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	} else if(algorithm==FLEM) {
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		CalculateSlope = &DEMObject::CalculateFleming;
	} else if(algorithm==D8) {
		CalculateSlope = &DEMObject::CalculateHick;
	} else {
		throw InvalidArgumentException("Chosen slope algorithm not available", AT);
	}

	//Now, calculate the parameters using the previously defined function pointer
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	for ( size_t j = 0; j < nrows; j++ ) {
		for ( size_t i = 0; i < ncols; i++ ) {
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			if( grid2D(i,j) == IOUtils::nodata ) {
				if(update_flag&SLOPE) {
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					slope(i,j) = azi(i,j) = IOUtils::nodata;
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				}
				if(update_flag&CURVATURE) {
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					curvature(i,j) = IOUtils::nodata;
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				}
				if(update_flag&NORMAL) {
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					Nx(i,j) = Ny(i,j) = Nz(i,j) = IOUtils::nodata;
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				}
			} else {
				getNeighbours(i, j, A);
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				double new_slope, new_Nx, new_Ny, new_Nz;
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				(this->*CalculateSlope)(A, new_slope, new_Nx, new_Ny, new_Nz);
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				const double new_azi = CalculateAspect(new_Nx, new_Ny, new_Nz, new_slope);
				const double new_curvature = getCurvature(A);
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				if(update_flag&SLOPE) {
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					slope(i,j) = new_slope;
					azi(i,j) = new_azi;
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				}
				if(update_flag&CURVATURE) {
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					curvature(i,j) = new_curvature;
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				}
				if(update_flag&NORMAL) {
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					Nx(i,j) = new_Nx;
					Ny(i,j) = new_Ny;
					Nz(i,j) = new_Nz;
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				}
			}
		}
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	}

	if((update_flag&SLOPE) && (algorithm==D8)) { //extra processing required: discretization
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		for ( size_t j = 0; j < nrows; j++ ) {
			for ( size_t i = 0; i < ncols; i++ ) {
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					//TODO: process flats by an extra algorithm
					if(azi(i,j)!=IOUtils::nodata)
						azi(i,j) = fmod(floor( (azi(i,j)+22.5)/45. )*45., 360.);
					if(slope(i,j)!=IOUtils::nodata)
						slope(i,j) = floor( slope(i,j)+0.5 );
			}
		}
	}

	//Inform the user is some points have unexpectidly not been computed
	//(ie: there was an altitude but some parameters could not be computed)
	if(slope_failures>0 || curvature_failures>0) {
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		cerr << "[W] DEMObject: " << slope_failures << " point(s) have an elevation but no slope, " << curvature_failures << " point(s) have an elevation but no curvature." << std::endl;
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	}

} // end of CalculateAziSlope

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double DEMObject::CalculateAspect(const double& o_Nx, const double& o_Ny, const double& o_Nz, const double& o_slope, const double no_slope) {
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//Calculates the aspect at a given point knowing its normal vector and slope
//(direction of the normal pointing out of the surface, clockwise from north)
//This azimuth calculation is similar to Hodgson (1998)
//local_nodata is the value that we want to give to the aspect of points that don't have a slope
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//The value is a bearing (ie: deg, clockwise, 0=North)
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	if(o_Nx==IOUtils::nodata || o_Ny==IOUtils::nodata || o_Nz==IOUtils::nodata || o_slope==IOUtils::nodata) {
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		return IOUtils::nodata;
	}

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	if ( o_slope > 0. ) { //there is some slope
		if ( o_Nx == 0. ) { //no E-W slope, so it is purely N-S
			if ( o_Ny < 0. ) {
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				return(180.); // south facing
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			} else {
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				return (0.); // north facing
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			}
		} else { //there is a E-W slope
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			if ( o_Nx > 0. ) {
				return (90. - atan(o_Ny/o_Nx)*Cst::to_deg);
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			} else {
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				return (270. - atan(o_Ny/o_Nx)*Cst::to_deg);
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			}
		}
	} else { // if slope = 0
		return (no_slope);          // undefined or plain surface
	}
}


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void DEMObject::CalculateHick(double A[4][4], double& o_slope, double& o_Nx, double& o_Ny, double& o_Nz) {
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//This calculates the surface normal vector using the steepest slope method (Dunn and Hickey, 1998):
//the steepest slope found in the eight cells surrounding (i,j) is given to be the slope in (i,j)
//Beware, sudden steps could happen
	const double smax = steepestGradient(A); //steepest local gradient

	if(smax==IOUtils::nodata) {
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		o_slope = IOUtils::nodata;
		o_Nx = IOUtils::nodata;
		o_Ny = IOUtils::nodata;
		o_Nz = IOUtils::nodata;
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		slope_failures++;
	} else {
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		o_slope = atan(smax)*Cst::to_deg;
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		//Nx and Ny: x and y components of the normal pointing OUT of the surface
		if ( smax > 0. ) { //ie: there is some slope
			double dx_sum, dy_sum;
			surfaceGradient(dx_sum, dy_sum, A);
			if(dx_sum==IOUtils::nodata || dy_sum==IOUtils::nodata) {
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				o_Nx = IOUtils::nodata;
				o_Ny = IOUtils::nodata;
				o_Nz = IOUtils::nodata;
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				slope_failures++;
			} else {
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				o_Nx = -1.0 * dx_sum / (2. * cellsize);	//Nx=-dz/dx
				o_Ny = -1.0 * dy_sum / (2. * cellsize);	//Ny=-dz/dy
				o_Nz = 1.;				//Nz=1 (normalized by definition of Nx and Ny)
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			}
		} else { //ie: there is no slope
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			o_Nx = 0.;
			o_Ny = 0.;
			o_Nz = 1.;
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		}
	}
}

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void DEMObject::CalculateFleming(double A[4][4], double& o_slope, double& o_Nx, double& o_Ny, double& o_Nz) {
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//This calculates the surface normal vector using method by Fleming and Hoffer (1979)
	if(A[2][1]!=IOUtils::nodata && A[2][3]!=IOUtils::nodata && A[3][2]!=IOUtils::nodata && A[1][2]!=IOUtils::nodata) {
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		o_Nx = 0.5 * (A[2][1] - A[2][3]) / cellsize;
		o_Ny = 0.5 * (A[3][2] - A[1][2]) / cellsize;
		o_Nz = 1.;
		o_slope = atan( sqrt(o_Nx*o_Nx+o_Ny*o_Ny) ) * Cst::to_deg;
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	} else {
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		CalculateHick(A, o_slope, o_Nx, o_Ny, o_Nz);
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	}
}

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void DEMObject::CalculateHorn(double A[4][4], double& o_slope, double& o_Nx, double& o_Ny, double& o_Nz) {
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//This calculates the slope using the two eight neighbors method given in Horn (1981)
//This is also the algorithm used by ArcGIS
	if ( A[1][1]!=IOUtils::nodata && A[1][2]!=IOUtils::nodata && A[1][3]!=IOUtils::nodata &&
	     A[2][1]!=IOUtils::nodata && A[2][2]!=IOUtils::nodata && A[2][3]!=IOUtils::nodata &&
	     A[3][1]!=IOUtils::nodata && A[3][2]!=IOUtils::nodata && A[3][3]!=IOUtils::nodata) {
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		o_Nx = ((A[3][3]+2.*A[2][3]+A[1][3]) - (A[3][1]+2.*A[2][1]+A[1][1])) / (8.*cellsize);
		o_Ny = ((A[1][3]+2.*A[1][2]+A[1][1]) - (A[3][3]+2.*A[3][2]+A[3][1])) / (8.*cellsize);
		o_Nz = 1.;
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		//There is no difference between slope = acos(n_z/|n|) and slope = atan(sqrt(sx*sx+sy*sy))
		//slope = acos( (Nz / sqrt( Nx*Nx + Ny*Ny + Nz*Nz )) );
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		o_slope = atan( sqrt(o_Nx*o_Nx+o_Ny*o_Ny) ) * Cst::to_deg;
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	} else {
		//steepest slope method (Dunn and Hickey, 1998)
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		CalculateHick(A, o_slope, o_Nx, o_Ny, o_Nz);
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	}
}

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void DEMObject::CalculateCorripio(double A[4][4], double& o_slope, double& o_Nx, double& o_Ny, double& o_Nz) {
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//This calculates the surface normal vector using the two triangle method given in Corripio (2003) but cell centered instead of node centered (ie using a 3x3 grid instead of 2x2)
	if ( A[1][1]!=IOUtils::nodata && A[1][3]!=IOUtils::nodata && A[3][1]!=IOUtils::nodata && A[3][3]!=IOUtils::nodata) {
		// See Corripio (2003), knowing that here we normalize the result (divided by Nz=cellsize*cellsize) and that we are cell centered instead of node centered
		o_Nx = (A[3][1] + A[1][1] - A[3][3] - A[1][3]) / (2.*2.*cellsize);
		o_Ny = (A[3][1] - A[1][1] + A[3][3] - A[1][3]) / (2.*2.*cellsize);
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		o_Nz = 1.;
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		//There is no difference between slope = acos(n_z/|n|) and slope = atan(sqrt(sx*sx+sy*sy))
		//slope = acos( (Nz / sqrt( Nx*Nx + Ny*Ny + Nz*Nz )) );
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		o_slope = atan( sqrt(o_Nx*o_Nx+o_Ny*o_Ny) ) * Cst::to_deg;
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	} else {
		//steepest slope method (Dunn and Hickey, 1998)
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		CalculateHick(A, o_slope, o_Nx, o_Ny, o_Nz);
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	}
}

double DEMObject::getCurvature(double A[4][4]) {
//This methode computes the curvature of a specific cell
	if(A[2][2]!=IOUtils::nodata) {
		const double Zwe   = avgHeight(A[2][1], A[2][2], A[2][3]);
		const double Zsn   = avgHeight(A[1][2], A[2][2], A[3][2]);
		const double Zswne = avgHeight(A[3][1], A[2][2], A[1][3]);
		const double Znwse = avgHeight(A[1][1], A[2][2], A[3][3]);

		const double sqrt2 = sqrt(2.);
		double sum=0.;
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		size_t count=0;
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		if(Zwe!=IOUtils::nodata) {
			sum += 0.5*(A[2][2]-Zwe);
			count++;
		}
		if(Zsn!=IOUtils::nodata) {
			sum += 0.5*(A[2][2]-Zsn);
			count++;
		}
		if(Zswne!=IOUtils::nodata) {
			sum += 0.5*(A[2][2]-Zswne)/sqrt2;
			count++;
		}
		if(Znwse!=IOUtils::nodata) {
			sum += 0.5*(A[2][2]-Znwse)/sqrt2;
			count++;
		}

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		if(count != 0.) return 1./(double)count * sum;
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	}
	curvature_failures++;
	return IOUtils::nodata;
}

double DEMObject::steepestGradient(double A[4][4]) {
//best effort to calculate the local steepest gradient
	double smax=-1.;		//maximum slope of all neighboring slopes
	const double sqrt2=sqrt(2.);	//the weight of the 4 corner cells is increased by sqrt(2)

	if(A[2][2]!=IOUtils::nodata) {
		if(A[1][1]!=IOUtils::nodata)
			smax = MAX( smax, fabs(A[2][2] - A[1][1])/(cellsize*sqrt2) );
		if(A[1][2]!=IOUtils::nodata)
			smax = MAX( smax, fabs(A[2][2] - A[1][2])/(cellsize) );
		if(A[1][3]!=IOUtils::nodata)
			smax = MAX( smax, fabs(A[2][2] - A[1][3])/(cellsize*sqrt2) );
		if(A[2][1]!=IOUtils::nodata)
			smax = MAX( smax, fabs(A[2][2] - A[2][1])/(cellsize) );
		if(A[2][3]!=IOUtils::nodata)
			smax = MAX( smax, fabs(A[2][2] - A[2][3])/(cellsize) );
		if(A[3][1]!=IOUtils::nodata)
			smax = MAX( smax, fabs(A[2][2] - A[3][1])/(cellsize*sqrt2) );
		if(A[3][2]!=IOUtils::nodata)
			smax = MAX( smax, fabs(A[2][2] - A[3][2])/(cellsize) );
		if(A[3][3]!=IOUtils::nodata)
			smax = MAX( smax, fabs(A[2][2] - A[3][3])/(cellsize*sqrt2) );
	}

	if(smax<0.)
		return IOUtils::nodata;
	return smax;
}

double DEMObject::lineGradient(const double& A1, const double& A2, const double& A3) {
//best effort to calculate the local gradient
	if(A3!=IOUtils::nodata && A1!=IOUtils::nodata) {
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		return A3 - A1;
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	} else {
		if(A2!=IOUtils::nodata) {
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			if(A3!=IOUtils::nodata)
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				return (A3 - A2)*2.;
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			if(A1!=IOUtils::nodata)
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				return (A2 - A1)*2.;
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		}
	}

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	return IOUtils::nodata;
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}

double DEMObject::fillMissingGradient(const double& delta1, const double& delta2) {
//If a gradient could not be computed, try to fill it with some neighboring value
	if(delta1!=IOUtils::nodata && delta2!=IOUtils::nodata) {
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		return 0.5*(delta1+delta2);
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	} else {
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		if(delta1!=IOUtils::nodata) return delta1;
		if(delta2!=IOUtils::nodata) return delta2;
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	}

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	return IOUtils::nodata;
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}

void DEMObject::surfaceGradient(double& dx_sum, double& dy_sum, double A[4][4]) {
//Compute the gradient for a given cell (i,j) accross its eight surrounding cells (Horn, 1981)
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	double dx1 = lineGradient(A[3][1], A[3][2], A[3][3]);
	double dx2 = lineGradient(A[2][1], A[2][2], A[2][3]);
	double dx3 = lineGradient(A[1][1], A[1][2], A[1][3]);
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	double dy1 = lineGradient(A[3][1], A[2][1], A[1][1]);
	double dy2 = lineGradient(A[3][2], A[2][2], A[1][2]);
	double dy3 = lineGradient(A[3][3], A[2][3], A[1][3]);
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	//now trying to fill whatever could not be filled...
	if(dx1==IOUtils::nodata) dx1 = fillMissingGradient(dx2, dx3);
	if(dx2==IOUtils::nodata) dx2 = fillMissingGradient(dx1, dx3);
	if(dx3==IOUtils::nodata) dx3 = fillMissingGradient(dx1, dx2);
	if(dy1==IOUtils::nodata) dy1 = fillMissingGradient(dy2, dy3);
	if(dy2==IOUtils::nodata) dy2 = fillMissingGradient(dy1, dy3);
	if(dy3==IOUtils::nodata) dy3 = fillMissingGradient(dy1, dy2);

	if(dx1!=IOUtils::nodata && dy1!=IOUtils::nodata) {
		// principal axis twice to emphasize height difference in that direction
		dx_sum = (dx1 + 2.*dx2 + dx3) * 0.25;
		dy_sum = (dy1 + 2.*dy2 + dy3) * 0.25;
	} else {
		//if dx1==nodata, this also means that dx2==nodata and dx3==nodata
		//(otherwise, dx1 would have received a copy of either dx2 or dx3)
		dx_sum = IOUtils::nodata;
		dy_sum = IOUtils::nodata;
	}
}

double DEMObject::avgHeight(const double& z1, const double &z2, const double& z3) {
//this safely computes the average height accross a vector

	if(z1!=IOUtils::nodata && z3!=IOUtils::nodata) {
		return 0.5*(z1+z3);
	}
	if(z1!=IOUtils::nodata && z2!=IOUtils::nodata) {
		return 0.5*(z1+z2);
	}
	if(z3!=IOUtils::nodata && z2!=IOUtils::nodata) {
		return 0.5*(z3+z2);
	}

	return IOUtils::nodata;
}

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void DEMObject::getNeighbours(const size_t i, const size_t j, double A[4][4]) {
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//this fills a 3x3 table containing the neighboring values
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		A[1][1] = safeGet((signed)i-1, (signed)j+1);
		A[1][2] = safeGet((signed)i, (signed)j+1);
		A[1][3] = safeGet((signed)i+1, (signed)j+1);
		A[2][1] = safeGet((signed)i-1, (signed)j);
		A[2][2] = safeGet((signed)i, (signed)j);
		A[2][3] = safeGet((signed)i+1, (signed)j);
		A[3][1] = safeGet((signed)i-1, (signed)j-1);
		A[3][2] = safeGet((signed)i, (signed)j-1);
		A[3][3] = safeGet((signed)i+1, (signed)j-1);
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}

double DEMObject::safeGet(const int i, const int j)
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{//this function would allow reading the value of *any* point,
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//that is, even for coordinates outside of the grid (where it would return nodata)
//this is to make implementing the slope/curvature computation easier for edges, holes, etc

	if(i<0 || i>=(signed)ncols) {
		return IOUtils::nodata;
	}
	if(j<0 || j>=(signed)nrows) {
		return IOUtils::nodata;
	}
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	return grid2D((unsigned)i, (unsigned)j);
}

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std::iostream& operator<<(std::iostream& os, const DEMObject& dem) {
	os << dem.slope;
	os << dem.azi;
	os << dem.curvature;
	os << dem.Nx << dem.Ny << dem.Nz;
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