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// -*- C++ -*-
// $Id: dpencode.cpp,v 1.3 2009-09-08 16:06:32 robertl Exp $
//------------------------------------------------------------------------
//
// Original in JavaScript:
// PolylineEncoder.js copyright Mark McClure April/May 2007
//
// Translated to C++
// Copyright (C) 2009 S. Khai Mong <khai@mangrai.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.
//
// This program 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
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
// USA.
//
//------------------------------------------------------------------------
#include "dpencode.h"
#include <cmath>
#include <stack>
using std::vector;
using std::stack;
using std::string;
//------------------------------------------------------------------------
PolylineEncoder::PolylineEncoder(int numLevels, double zoomFactor, double vs):
numLevels(numLevels), verySmall(vs)
{
if (verySmall <=0.0) {
verySmall = 1.0E-5;
}
for (int i = 0; i < numLevels; i++) {
zoomLevelBreaks.push_back(verySmall*pow(zoomFactor, numLevels-i-1));
}
}
//------------------------------------------------------------------------
class IntervalPair
{
public:
IntervalPair(int i0, int i1): i0(i0), i1(i1)
{
}
int i0, i1;
};
//------------------------------------------------------------------------
static double hypotenuse(double a, double b)
{
return sqrt(a*a + b*b);
}
//------------------------------------------------------------------------
static double hdist(const LatLng& a, const LatLng& b)
{
return hypotenuse(a.lat()-b.lat(), a.lng()-b.lng());
}
//------------------------------------------------------------------------
static string encodeNumber(int num)
{
string encodeString = "";
while (num >= 0x20) {
encodeString += char((0x20 | (num & 0x1f)) + 63);
num = num >> 5;
}
encodeString += char(num + 63);
return encodeString;
}
//------------------------------------------------------------------------
// This one is Google's verbatim.
static string encodeSignedNumber(int num)
{
int sgn_num = num << 1;
if (num < 0) {
sgn_num = ~(sgn_num);
}
return (encodeNumber(sgn_num));
}
//------------------------------------------------------------------------
int roundToInt(double x)
{
return (x>0.0) ? int(x+0.5) : int(x-0.5);
}
//------------------------------------------------------------------------
void PolylineEncoder::createEncodings(string& encoded_points,
const vector <LatLng>& points,
const vector <double>& dists)
{
encoded_points = "";
int plat = 0;
int plng = 0;
for (unsigned int i = 0; i < points.size(); i++) {
if (dists[i] >= 0.0 || i == 0 || i == points.size()-1) {
int late5 = roundToInt(points[i].lat() * 1e5);
int lnge5 = roundToInt(points[i].lng() * 1e5);
int dlat = late5 - plat;
int dlng = lnge5 - plng;
encoded_points += encodeSignedNumber(dlat) + encodeSignedNumber(dlng);
plat = late5;
plng = lnge5;
}
}
}
//------------------------------------------------------------------------
// This computes the appropriate zoom level of a point in terms of it's
// distance from the relevant segment in the DP algorithm. Could be done
// in terms of a logarithm, but this approach makes it a bit easier to
// ensure that the level is not too large.
int PolylineEncoder::computeLevel(double dd)
{
int lev = 0;
if (dd > verySmall) {
while (dd < zoomLevelBreaks[lev]) {
lev++;
}
}
return lev;
}
//------------------------------------------------------------------------
// Now we can use the previous function to march down the list
// of points and encode the levels. Like createEncodings, we
// ignore points whose distance (in dists) is undefined.
void PolylineEncoder::encodeLevels(string& encoded_levels, const vector<LatLng>& points, const vector<double>& dists)
{
encoded_levels = "";
encoded_levels += encodeNumber(numLevels-1);
for (unsigned int i=1; i<points.size()-1; i++) {
if (dists[i] >= 0.0) {
encoded_levels += encodeNumber(numLevels-computeLevel(dists[i])-1);
}
}
encoded_levels += encodeNumber(numLevels-1);
}
//------------------------------------------------------------------------
double PolylineEncoder::distance(const LatLng& p0, const LatLng& p1, const LatLng& p2)
{
double out = 0.0;
if (p1.lat() == p2.lat() && p1.lng() == p2.lng()) {
out = hdist(p2, p0);
} else {
double dlat = (p2.lat()-p1.lat());
double dlng = (p2.lng()-p1.lng());
double u = ((p0.lat()-p1.lat())*dlat+(p0.lng()-p1.lng())*dlng)/(dlat*dlat + dlng*dlng);
if (u <= 0) {
out = hdist(p0, p1);
} else if (u >= 1) {
out = hdist(p0, p2);
} else {
out = hdist(p0, LatLng(p1.lat() + u*dlat, p1.lng() + u*dlng));
}
}
return out;
}
//------------------------------------------------------------------------
void PolylineEncoder::dpEncode(string& encPts, string& encLevels, const vector<LatLng>& points)
{
if (points.size() < 2) {
encPts = encLevels = ""; // no solution here.
return;
}
stack <IntervalPair> stk;
vector <double> dists(points.size(), -1.0);
stk.push(IntervalPair(0, int(points.size())-1));
while (!stk.empty()) {
IntervalPair current = stk.top();
stk.pop();
double maxDist = -1.0;
int maxLoc = -1;
for (int i=current.i0+1; i<current.i1; i++) {
double dist = this->distance(points[i], points[current.i0], points[current.i1]);
if (dist > maxDist) {
maxDist = dist;
maxLoc = i;
}
}
if (maxDist > this->verySmall) {
dists[maxLoc] = maxDist;
stk.push(IntervalPair(current.i0, maxLoc));
stk.push(IntervalPair(maxLoc, current.i1));
}
}
createEncodings(encPts, points, dists);
encodeLevels(encLevels, points, dists);
}
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