src/analysis/vector/qgszonalstatistics.cpp

Go to the documentation of this file.

/***************************************************************************
                          qgszonalstatistics.cpp  -  description
                          ----------------------------
    begin                : August 29th, 2009
    copyright            : (C) 2009 by Marco Hugentobler
    email                : marco at hugis dot net
 ***************************************************************************/

/***************************************************************************
 *                                                                         *
 *   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 "qgszonalstatistics.h"
#include "qgsgeometry.h"
#include "qgsvectordataprovider.h"
#include "qgsvectorlayer.h"
#include "gdal.h"
#include "cpl_string.h"
#include <QProgressDialog>

#if defined(GDAL_VERSION_NUM) && GDAL_VERSION_NUM >= 1800
#define TO8(x) (x).toUtf8().constData()
#else
#define TO8(x) (x).toLocal8Bit().constData()
#endif

QgsZonalStatistics::QgsZonalStatistics( QgsVectorLayer* polygonLayer, const QString& rasterFile, const QString& attributePrefix, int rasterBand )
    : mRasterFilePath( rasterFile )
    , mRasterBand( rasterBand )
    , mPolygonLayer( polygonLayer )
    , mAttributePrefix( attributePrefix )
    , mInputNodataValue( -1 )
{

}

QgsZonalStatistics::QgsZonalStatistics()
    : mRasterBand( 0 )
    , mPolygonLayer( 0 )
{

}

QgsZonalStatistics::~QgsZonalStatistics()
{

}

int QgsZonalStatistics::calculateStatistics( QProgressDialog* p )
{
  if ( !mPolygonLayer || mPolygonLayer->geometryType() != QGis::Polygon )
  {
    return 1;
  }

  QgsVectorDataProvider* vectorProvider = mPolygonLayer->dataProvider();
  if ( !vectorProvider )
  {
    return 2;
  }

  //open the raster layer and the raster band
  GDALAllRegister();
  GDALDatasetH inputDataset = GDALOpen( TO8( mRasterFilePath ), GA_ReadOnly );
  if ( inputDataset == NULL )
  {
    return 3;
  }

  if ( GDALGetRasterCount( inputDataset ) < ( mRasterBand - 1 ) )
  {
    GDALClose( inputDataset );
    return 4;
  }

  GDALRasterBandH rasterBand = GDALGetRasterBand( inputDataset, mRasterBand );
  if ( rasterBand == NULL )
  {
    GDALClose( inputDataset );
    return 5;
  }
  mInputNodataValue = GDALGetRasterNoDataValue( rasterBand, NULL );

  //get geometry info about raster layer
  int nCellsXGDAL = GDALGetRasterXSize( inputDataset );
  int nCellsYGDAL = GDALGetRasterYSize( inputDataset );
  double geoTransform[6];
  if ( GDALGetGeoTransform( inputDataset, geoTransform ) != CE_None )
  {
    GDALClose( inputDataset );
    return 6;
  }
  double cellsizeX = geoTransform[1];
  if ( cellsizeX < 0 )
  {
    cellsizeX = -cellsizeX;
  }
  double cellsizeY = geoTransform[5];
  if ( cellsizeY < 0 )
  {
    cellsizeY = -cellsizeY;
  }
  QgsRectangle rasterBBox( geoTransform[0], geoTransform[3] - ( nCellsYGDAL * cellsizeY ),
                           geoTransform[0] + ( nCellsXGDAL * cellsizeX ), geoTransform[3] );

  //add the new count, sum, mean fields to the provider
  QList<QgsField> newFieldList;
  QgsField countField( mAttributePrefix + "count", QVariant::Double, "double precision" );
  QgsField sumField( mAttributePrefix + "sum", QVariant::Double, "double precision" );
  QgsField meanField( mAttributePrefix + "mean", QVariant::Double, "double precision" );
  newFieldList.push_back( countField );
  newFieldList.push_back( sumField );
  newFieldList.push_back( meanField );
  vectorProvider->addAttributes( newFieldList );

  //index of the new fields
  int countIndex = vectorProvider->fieldNameIndex( mAttributePrefix + "count" );
  int sumIndex = vectorProvider->fieldNameIndex( mAttributePrefix + "sum" );
  int meanIndex = vectorProvider->fieldNameIndex( mAttributePrefix + "mean" );

  if ( countIndex == -1 || sumIndex == -1 || meanIndex == -1 )
  {
    return 8;
  }

  //progress dialog
  long featureCount = vectorProvider->featureCount();
  if ( p )
  {
    p->setMaximum( featureCount );
  }


  //iterate over each polygon
  QgsFeatureRequest request;
  request.setSubsetOfAttributes( QgsAttributeList() );
  QgsFeatureIterator fi = vectorProvider->getFeatures( request );
  QgsFeature f;
  double count = 0;
  double sum = 0;
  double mean = 0;
  int featureCounter = 0;

  while ( fi.nextFeature( f ) )
  {
    if ( p )
    {
      p->setValue( featureCounter );
    }

    if ( p && p->wasCanceled() )
    {
      break;
    }

    QgsGeometry* featureGeometry = f.geometry();
    if ( !featureGeometry )
    {
      ++featureCounter;
      continue;
    }

    QgsRectangle featureRect = featureGeometry->boundingBox().intersect( &rasterBBox );
    if ( featureRect.isEmpty() )
    {
      ++featureCounter;
      continue;
    }

    int offsetX, offsetY, nCellsX, nCellsY;
    if ( cellInfoForBBox( rasterBBox, featureRect, cellsizeX, cellsizeY, offsetX, offsetY, nCellsX, nCellsY ) != 0 )
    {
      ++featureCounter;
      continue;
    }

    //avoid access to cells outside of the raster (may occur because of rounding)
    if (( offsetX + nCellsX ) > nCellsXGDAL )
    {
      nCellsX = nCellsXGDAL - offsetX;
    }
    if (( offsetY + nCellsY ) > nCellsYGDAL )
    {
      nCellsY = nCellsYGDAL - offsetY;
    }

    statisticsFromMiddlePointTest( rasterBand, featureGeometry, offsetX, offsetY, nCellsX, nCellsY, cellsizeX, cellsizeY,
                                   rasterBBox, sum, count );

    if ( count <= 1 )
    {
      //the cell resolution is probably larger than the polygon area. We switch to precise pixel - polygon intersection in this case
      statisticsFromPreciseIntersection( rasterBand, featureGeometry, offsetX, offsetY, nCellsX, nCellsY, cellsizeX, cellsizeY,
                                         rasterBBox, sum, count );
    }


    if ( count == 0 )
    {
      mean = 0;
    }
    else
    {
      mean = sum / count;
    }

    //write the statistics value to the vector data provider
    QgsChangedAttributesMap changeMap;
    QgsAttributeMap changeAttributeMap;
    changeAttributeMap.insert( countIndex, QVariant( count ) );
    changeAttributeMap.insert( sumIndex, QVariant( sum ) );
    changeAttributeMap.insert( meanIndex, QVariant( mean ) );
    changeMap.insert( f.id(), changeAttributeMap );
    vectorProvider->changeAttributeValues( changeMap );

    ++featureCounter;
  }

  if ( p )
  {
    p->setValue( featureCount );
  }

  GDALClose( inputDataset );

  if ( p && p->wasCanceled() )
  {
    return 9;
  }

  return 0;
}

int QgsZonalStatistics::cellInfoForBBox( const QgsRectangle& rasterBBox, const QgsRectangle& featureBBox, double cellSizeX, double cellSizeY,
    int& offsetX, int& offsetY, int& nCellsX, int& nCellsY ) const
{
  //get intersecting bbox
  QgsRectangle intersectBox = rasterBBox.intersect( &featureBBox );
  if ( intersectBox.isEmpty() )
  {
    nCellsX = 0; nCellsY = 0; offsetX = 0; offsetY = 0;
    return 0;
  }

  //get offset in pixels in x- and y- direction
  offsetX = ( int )(( intersectBox.xMinimum() - rasterBBox.xMinimum() ) / cellSizeX );
  offsetY = ( int )(( rasterBBox.yMaximum() - intersectBox.yMaximum() ) / cellSizeY );

  int maxColumn = ( int )(( intersectBox.xMaximum() - rasterBBox.xMinimum() ) / cellSizeX ) + 1;
  int maxRow = ( int )(( rasterBBox.yMaximum() - intersectBox.yMinimum() ) / cellSizeY ) + 1;

  nCellsX = maxColumn - offsetX;
  nCellsY = maxRow - offsetY;

  return 0;
}

void QgsZonalStatistics::statisticsFromMiddlePointTest( void* band, QgsGeometry* poly, int pixelOffsetX,
    int pixelOffsetY, int nCellsX, int nCellsY, double cellSizeX, double cellSizeY, const QgsRectangle& rasterBBox, double& sum, double& count )
{
  double cellCenterX, cellCenterY;

  float* scanLine = ( float * ) CPLMalloc( sizeof( float ) * nCellsX );
  cellCenterY = rasterBBox.yMaximum() - pixelOffsetY * cellSizeY - cellSizeY / 2;
  count = 0;
  sum = 0;

  GEOSGeometry* polyGeos = poly->asGeos();
  if ( !polyGeos )
  {
    return;
  }

  const GEOSPreparedGeometry* polyGeosPrepared = GEOSPrepare( poly->asGeos() );
  if ( !polyGeosPrepared )
  {
    return;
  }

  GEOSCoordSequence* cellCenterCoords = 0;
  GEOSGeometry* currentCellCenter = 0;

  for ( int i = 0; i < nCellsY; ++i )
  {
    if ( GDALRasterIO( band, GF_Read, pixelOffsetX, pixelOffsetY + i, nCellsX, 1, scanLine, nCellsX, 1, GDT_Float32, 0, 0 )
         != CPLE_None )
    {
      continue;
    }
    cellCenterX = rasterBBox.xMinimum() + pixelOffsetX * cellSizeX + cellSizeX / 2;
    for ( int j = 0; j < nCellsX; ++j )
    {
      GEOSGeom_destroy( currentCellCenter );
      cellCenterCoords = GEOSCoordSeq_create( 1, 2 );
      GEOSCoordSeq_setX( cellCenterCoords, 0, cellCenterX );
      GEOSCoordSeq_setY( cellCenterCoords, 0, cellCenterY );
      currentCellCenter = GEOSGeom_createPoint( cellCenterCoords );

      if ( GEOSPreparedContains( polyGeosPrepared, currentCellCenter ) )
      {
        if ( scanLine[j] != mInputNodataValue ) //don't consider nodata values
        {
          sum += scanLine[j];
          ++count;
        }
      }
      cellCenterX += cellSizeX;
    }
    cellCenterY -= cellSizeY;
  }
  CPLFree( scanLine );
  GEOSPreparedGeom_destroy( polyGeosPrepared );
}

void QgsZonalStatistics::statisticsFromPreciseIntersection( void* band, QgsGeometry* poly, int pixelOffsetX,
    int pixelOffsetY, int nCellsX, int nCellsY, double cellSizeX, double cellSizeY, const QgsRectangle& rasterBBox, double& sum, double& count )
{
  sum = 0;
  count = 0;
  double currentY = rasterBBox.yMaximum() - pixelOffsetY * cellSizeY - cellSizeY / 2;
  float* pixelData = ( float * ) CPLMalloc( sizeof( float ) );
  QgsGeometry* pixelRectGeometry = 0;

  double hCellSizeX = cellSizeX / 2.0;
  double hCellSizeY = cellSizeY / 2.0;
  double pixelArea = cellSizeX * cellSizeY;
  double weight = 0;

  for ( int row = 0; row < nCellsY; ++row )
  {
    double currentX = rasterBBox.xMinimum() + cellSizeX / 2.0 + pixelOffsetX * cellSizeX;
    for ( int col = 0; col < nCellsX; ++col )
    {
      GDALRasterIO( band, GF_Read, pixelOffsetX + col, pixelOffsetY + row, nCellsX, 1, pixelData, 1, 1, GDT_Float32, 0, 0 );
      pixelRectGeometry = QgsGeometry::fromRect( QgsRectangle( currentX - hCellSizeX, currentY - hCellSizeY, currentX + hCellSizeX, currentY + hCellSizeY ) );
      if ( pixelRectGeometry )
      {
        //intersection
        QgsGeometry *intersectGeometry = pixelRectGeometry->intersection( poly );
        if ( intersectGeometry )
        {
          double intersectionArea = intersectGeometry->area();
          if ( intersectionArea >= 0.0 )
          {
            weight = intersectionArea / pixelArea;
            count += weight;
            sum += *pixelData * weight;
          }
          delete intersectGeometry;
        }
      }
      currentX += cellSizeX;
    }
    currentY -= cellSizeY;
  }
  CPLFree( pixelData );
}