qgshillshadefilter.cpp

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/***************************************************************************
                          qgshillshadefilter.h  -  description
                          --------------------------------
    begin                : September 26th, 2011
    copyright            : (C) 2011 by Marco Hugentobler
    email                : marco dot hugentobler at sourcepole dot ch
 ***************************************************************************/

/***************************************************************************
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 ***************************************************************************/

#include "qgshillshadefilter.h"
#include <cmath>

QgsHillshadeFilter::QgsHillshadeFilter( const QString &inputFile, const QString &outputFile, const QString &outputFormat, double lightAzimuth,
                                        double lightAngle )
  : QgsDerivativeFilter( inputFile, outputFile, outputFormat )
  , mLightAzimuth( lightAzimuth )
  , mLightAngle( lightAngle )
{
}

float QgsHillshadeFilter::processNineCellWindow( float *x11, float *x21, float *x31,
    float *x12, float *x22, float *x32,
    float *x13, float *x23, float *x33 )
{
  float derX = calcFirstDerX( x11, x21, x31, x12, x22, x32, x13, x23, x33 );
  float derY = calcFirstDerY( x11, x21, x31, x12, x22, x32, x13, x23, x33 );

  if ( derX == mOutputNodataValue || derY == mOutputNodataValue )
  {
    return mOutputNodataValue;
  }

  float zenith_rad = mLightAngle * M_PI / 180.0;
  float slope_rad = std::atan( std::sqrt( derX * derX + derY * derY ) );
  float azimuth_rad = mLightAzimuth * M_PI / 180.0;
  float aspect_rad = 0;
  if ( derX == 0 && derY == 0 ) //aspect undefined, take a neutral value. Better solutions?
  {
    aspect_rad = azimuth_rad / 2.0;
  }
  else
  {
    aspect_rad = M_PI + std::atan2( derX, derY );
  }
  return std::max( 0.0, 255.0 * ( ( std::cos( zenith_rad ) * std::cos( slope_rad ) ) + ( std::sin( zenith_rad ) * std::sin( slope_rad ) * std::cos( azimuth_rad - aspect_rad ) ) ) );
}