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lib refactoring

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git-svn-id: http://svn.osgeo.org/qgis/trunk/qgis@4592 c8812cc2-4d05-0410-92ff-de0c093fc19c
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timlinux 2006-01-08 01:32:16 +00:00
parent f43206d1ed
commit 8e8ba46460
1 changed files with 0 additions and 106 deletions
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src/qgsscalecalculator.cpp
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/***************************************************************************
qgsscalecalculator.h
Calculates scale based on map extent and units
-------------------
begin : May 18, 2004
copyright : (C) 2004 by Gary E.Sherman
email : sherman at mrcc.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. *
* *
***************************************************************************/
/* $Id$ */
#include <assert.h>
#include <math.h>
#include <qstring.h>
#include "qgsrect.h"
#include "qgsscalecalculator.h"
QgsScaleCalculator::QgsScaleCalculator(int dpi, QGis::units mapUnits)
: mDpi(dpi), mMapUnits(mapUnits)
{}
QgsScaleCalculator::~QgsScaleCalculator()
{}
void QgsScaleCalculator::setDpi(int dpi)
{
mDpi = dpi;
}
void QgsScaleCalculator::setMapUnits(QGis::units mapUnits)
{
mMapUnits = mapUnits;
}
double QgsScaleCalculator::calculate(QgsRect &mapExtent, int canvasWidth)
{
double conversionFactor;
double delta;
// calculation is based on the map units and extent, the dpi of the
// users display, and the canvas width
switch(mMapUnits)
{
case QGis::METERS:
// convert meters to inches
conversionFactor = 39.3700787;
delta = mapExtent.xMax() - mapExtent.xMin();
break;
case QGis::FEET:
conversionFactor = 12.0;
delta = mapExtent.xMax() - mapExtent.xMin();
break;
case QGis::DEGREES:
// degrees require conversion to meters first
conversionFactor = 39.3700787;
delta = calculateGeographicDistance(mapExtent);
break;
default:
assert("bad map units");
break;
}
#ifdef QGISDEBUG
std::cerr << "Using conversionFactor of " << conversionFactor << std::endl;
#endif
double scale = (delta * conversionFactor)/(canvasWidth/mDpi);
return scale;
}
double QgsScaleCalculator::calculateGeographicDistance(QgsRect &mapExtent)
{
// need to calculate the x distance in meters
// We'll use the middle latitude for the calculation
// Note this is an approximation (although very close) but calculating scale
// for geographic data over large extents is quasi-meaningless
double lat1 = (mapExtent.yMax() - mapExtent.yMin())/2 + mapExtent.yMin();
double lat2 = lat1;
double lon1 = mapExtent.xMin();
double lon2 = mapExtent.xMax();
double dlon = lon2 - lon1;
double dlat = lat2 - lat1;
double rads = (4 * atan(1.0))/180;
double a = pow((sin(dlat*rads/2)),2) +
cos(lat1 *rads) * cos(lat2 *rads) *pow(sin(dlon*rads/2),2);
double c = 2 * atan2(sqrt(a), sqrt(1-a));
// calculate radius of earth
double ra = 6378;
// unused! double rb = 6357;
double e = .081082;
double R = ra* sqrt(1-pow(e,2))/(1 - pow(e,2)*pow(sin(lat1*rads),2));
double d = c *R; // kilometers;
double meters = d * 1000.0;
#ifdef QGISDEBUG
std::cerr << "Distance across map extent (m): " << meters << std::endl;
#endif
return meters;
}