qgstolerance.cpp

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/***************************************************************************
    qgstolerance.cpp  -  wrapper for tolerance handling
    ----------------------
    begin                : March 2009
    copyright            : (C) 2009 by Richard Kostecky
    email                : csf.kostej at gmail dot com
 ***************************************************************************
 *                                                                         *
 *   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 "qgstolerance.h"
#include <QSettings>
#include <QPoint>
#include <cmath>

double QgsTolerance::toleranceInMapUnits( double tolerance, QgsMapLayer* layer, QgsMapRenderer* renderer, UnitType units )
{
  if ( units == MapUnits )
  {
    return tolerance;
  }
  double mapUnitsPerPixel = computeMapUnitPerPixel( layer, renderer );
  return tolerance * mapUnitsPerPixel;
}


double QgsTolerance::vertexSearchRadius( QgsMapLayer* layer, QgsMapRenderer* renderer )
{
  QSettings settings;
  double tolerance = settings.value( "/qgis/digitizing/search_radius_vertex_edit", 10 ).toDouble();
  UnitType units = ( QgsTolerance::UnitType ) settings.value( "/qgis/digitizing/search_radius_vertex_edit_unit", QgsTolerance::Pixels ).toInt();
  return toleranceInMapUnits( tolerance, layer, renderer, units );
}


double QgsTolerance::defaultTolerance( QgsMapLayer* layer, QgsMapRenderer* renderer )
{
  QSettings settings;
  double tolerance = settings.value( "/qgis/digitizing/default_snapping_tolerance", 0 ).toDouble();
  UnitType units = ( QgsTolerance::UnitType ) settings.value( "/qgis/digitizing/default_snapping_tolerance_unit", 0 ).toInt();
  return toleranceInMapUnits( tolerance, layer, renderer, units );
}


double QgsTolerance::computeMapUnitPerPixel( QgsMapLayer* layer, QgsMapRenderer* renderer )
{
  if ( ! renderer->hasCrsTransformEnabled() )
  {
    // if the on-the-fly projections are not enabled, layer units pre pixel are the same as map units per pixel
    return renderer->mapUnitsPerPixel();
  }

  // the layer is projected. Find out how many pixels are in one map unit - either horizontal and vertical direction
  // this check might not work correctly in some cases
  // (on a large area the pixels projected around "0,0" can have different properties from the actual point)
  QgsPoint p1 = toLayerCoordinates( layer, renderer, QPoint( 0, 1 ) );
  QgsPoint p2 = toLayerCoordinates( layer, renderer, QPoint( 0, 2 ) );
  QgsPoint p3 = toLayerCoordinates( layer, renderer, QPoint( 1, 0 ) );
  QgsPoint p4 = toLayerCoordinates( layer, renderer, QPoint( 2, 0 ) );
  double x = p1.sqrDist( p2 );
  double y = p3.sqrDist( p4 );
  if ( x > y )
  {
    return sqrt( x );
  }
  else
  {
    return sqrt( y );
  }
}


QgsPoint QgsTolerance::toLayerCoordinates( QgsMapLayer* layer, QgsMapRenderer* renderer, const QPoint& point )
{
  QgsPoint pt = renderer->coordinateTransform()->toMapCoordinates( point );
  return renderer->mapToLayerCoordinates( layer, pt );
}