com.graphhopper.reader.dem.GraphElevationSmoothing Maven / Gradle / Ivy
package com.graphhopper.reader.dem;
import com.graphhopper.util.DistancePlaneProjection;
import com.graphhopper.util.PointList;
/**
* This class smooths the elevation data of a PointList by calculating the average elevation over
* multiple points of that PointList.
*
* The ElevationData is read from rectangular tiles. Especially when going along a cliff,
* valley, or pass, it can happen that a small part of the road contains incorrect elevation data.
* This is because the elevation data is coarse and sometimes contains errors.
*
* This can lead to incorrect ascend, descend, and distance calculation of a route.
*
* @author Robin Boldt
*/
public class GraphElevationSmoothing {
// If the point is farther then this, we stop averaging
private final static int MAX_SEARCH_DISTANCE = 150;
public static PointList smoothElevation(PointList geometry) {
for (int i = 1; i < geometry.size() - 1; i++) {
int start = i;
for (int j = i-1; j >= 0 ; j--) {
if (MAX_SEARCH_DISTANCE > DistancePlaneProjection.DIST_PLANE.calcDist(geometry.getLat(i), geometry.getLon(i), geometry.getLat(j), geometry.getLon(j))) {
start = j;
}else{
break;
}
}
int end = i;
for (int j = i+1; j < geometry.size(); j++) {
if (MAX_SEARCH_DISTANCE > DistancePlaneProjection.DIST_PLANE.calcDist(geometry.getLat(i), geometry.getLon(i), geometry.getLat(j), geometry.getLon(j))) {
// +1 because the end is exclusive
end = j+1;
}else{
break;
}
}
// In this case we cannot find any points within the max search distance, so we simply skip this point
if(start == end)
continue;
double sum = 0;
for (int j = start; j < end; j++) {
// We skip points that are too far away, important for motorways
if (MAX_SEARCH_DISTANCE > DistancePlaneProjection.DIST_PLANE.calcDist(geometry.getLat(i), geometry.getLon(i), geometry.getLat(j), geometry.getLon(j))) {
sum += geometry.getEle(j);
}
}
double smoothed = sum / (end-start);
geometry.setElevation(i, smoothed);
}
return geometry;
}
}