//Check if the lines are interescting in 2d space
//Alternative version from http://thirdpartyninjas.com/blog/2008/10/07/line-segment-intersection/
public static bool LineLineIntersection(out GeoPoint intersection, GeoSegment line1, GeoSegment line2)
{
bool isIntersecting = false;
intersection = GeoPoint.Zero;
//3d -> 2d
double p1_x = line1.Start.Longitude;
double p1_y = line1.Start.Latitude;
double p2_x = line1.End.Longitude;
double p2_y = line1.End.Latitude;
double p3_x = line2.Start.Longitude;
double p3_y = line2.Start.Latitude;
double p4_x = line2.End.Longitude;
double p4_y = line2.End.Latitude;
double denominator = (p4_y - p3_y) * (p2_x - p1_x) - (p4_x - p3_x) * (p2_y - p1_y);
//Make sure the denominator is > 0, if so the lines are parallel
if (denominator != 0)
{
double u_a = ((p4_x - p3_x) * (p1_y - p3_y) - (p4_y - p3_y) * (p1_x - p3_x)) / denominator;
double u_b = ((p2_x - p1_x) * (p1_y - p3_y) - (p2_y - p1_y) * (p1_x - p3_x)) / denominator;
//Is intersecting if u_a and u_b are between 0 and 1
if (u_a >= 0 && u_a <= 1 && u_b >= 0 && u_b <= 1)
{
intersection = new GeoPoint(p1_y + u_a * (p2_y - p1_y), p1_x + u_a * (p2_x - p1_x));
isIntersecting = true;
}
}
return(isIntersecting);
}
public IEnumerable <GeoSegment> GetDEMNorthSouthLines(List <FileMetadata> segTiles, GeoPoint westernSegPoint, GeoPoint easternSegPoint)
{
// Get the first north west tile and last south east tile.
// The lines are bounded by those tiles
foreach (var tilesByX in segTiles.GroupBy(t => t.StartLon).OrderBy(g => g.Key))
{
List <FileMetadata> NSTilesOrdered = tilesByX.OrderByDescending(t => t.StartLat).ToList();
FileMetadata top = NSTilesOrdered.First();
FileMetadata bottom = NSTilesOrdered.Last();
// TIP: can optimize here starting with min(westernSegPoint, startlon) but careful !
GeoPoint curPoint = new GeoPoint(top.StartLat, top.StartLon);
// X Index in tile coords
int curIndex = (int)Math.Ceiling((curPoint.Longitude - top.StartLon) / top.PixelScaleX);
while (IsPointInTile(top, curPoint))
{
if (curIndex >= top.Width)
{
break;
}
curPoint.Longitude = top.StartLon + (top.pixelSizeX * curIndex);
if (curPoint.Longitude > easternSegPoint.Longitude)
{
break;
}
GeoSegment line = new GeoSegment(new GeoPoint(top.OriginLatitude, curPoint.Longitude), new GeoPoint(bottom.EndLatitude, curPoint.Longitude));
curIndex++;
yield return(line);
}
}
}
public IEnumerable <GeoSegment> GetDEMWestEastLines(List <FileMetadata> segTiles, GeoPoint northernSegPoint, GeoPoint southernSegPoint)
{
// Get the first north west tile and last south east tile.
// The lines are bounded by those tiles
foreach (var tilesByY in segTiles.GroupBy(t => t.StartLat).OrderByDescending(g => g.Key))
{
List <FileMetadata> WETilesOrdered = tilesByY.OrderBy(t => t.StartLon).ToList();
FileMetadata left = WETilesOrdered.First();
FileMetadata right = WETilesOrdered.Last();
GeoPoint curPoint = new GeoPoint(left.StartLat, left.StartLon);
// Y Index in tile coords
int curIndex = (int)Math.Ceiling((left.StartLat - curPoint.Latitude) / left.PixelScaleY);
while (IsPointInTile(left, curPoint))
{
if (curIndex >= left.Height)
{
break;
}
curPoint.Latitude = left.StartLat + (left.pixelSizeY * curIndex);
if (curPoint.Latitude < southernSegPoint.Latitude)
{
break;
}
GeoSegment line = new GeoSegment(new GeoPoint(curPoint.Latitude, left.OriginLongitude), new GeoPoint(curPoint.Latitude, right.EndLongitude));
curIndex++;
yield return(line);
}
}
}
/// <summary>
/// Finds all intersections between given segment and DEM grid
/// </summary>
/// <param name="startLon">Segment start longitude</param>
/// <param name="startLat">Segment start latitude</param>
/// <param name="endLon">Segment end longitude</param>
/// <param name="endLat">Segment end latitude</param>
/// <param name="segTiles">Metadata files <see cref="GeoTiffService.GetCoveringFiles"/> to see how to get them relative to segment geometry</param>
/// <param name="returnStartPoint">If true, the segment starting point will be returned. Useful when processing a line segment by segment.</param>
/// <param name="returnEndPoind">If true, the segment end point will be returned. Useful when processing a line segment by segment.</param>
/// <returns></returns>
public List <GeoPoint> FindSegmentIntersections(double startLon, double startLat, double endLon, double endLat, List <FileMetadata> segTiles, bool returnStartPoint, bool returnEndPoind)
{
List <GeoPoint> segmentPointsWithDEMPoints;
// Find intersections with north/south lines,
// starting form segment western point to easternmost point
GeoPoint westernSegPoint = startLon < endLon ? new GeoPoint(startLat, startLon) : new GeoPoint(endLat, endLon);
GeoPoint easternSegPoint = startLon > endLon ? new GeoPoint(startLat, startLon) : new GeoPoint(endLat, endLon);
GeoSegment inputSegment = new GeoSegment(westernSegPoint, easternSegPoint);
if (segTiles.Any())
{
int estimatedCapacity = (segTiles.Select(t => t.OriginLongitude).Distinct().Count() // num horizontal tiles * width
* segTiles.First().Width)
+ (segTiles.Select(t => t.OriginLatitude).Distinct().Count() // num vertical tiles * height
* segTiles.First().Height);
segmentPointsWithDEMPoints = new List <GeoPoint>(estimatedCapacity);
bool yAxisDown = segTiles.First().pixelSizeY < 0;
if (yAxisDown == false)
{
throw new NotImplementedException("DEM with y axis upwards not supported.");
}
foreach (GeoSegment demSegment in this.GetDEMNorthSouthLines(segTiles, westernSegPoint, easternSegPoint))
{
GeoPoint intersectionPoint = null;
if (GeometryService.LineLineIntersection(out intersectionPoint, inputSegment, demSegment))
{
segmentPointsWithDEMPoints.Add(intersectionPoint);
}
}
// Find intersections with west/east lines,
// starting form segment northernmost point to southernmost point
GeoPoint northernSegPoint = startLat > endLat ? new GeoPoint(startLat, startLon) : new GeoPoint(endLat, endLon);
GeoPoint southernSegPoint = startLat < endLat ? new GeoPoint(startLat, startLon) : new GeoPoint(endLat, endLon);
inputSegment = new GeoSegment(northernSegPoint, southernSegPoint);
foreach (GeoSegment demSegment in this.GetDEMWestEastLines(segTiles, northernSegPoint, southernSegPoint))
{
GeoPoint intersectionPoint = null;
if (GeometryService.LineLineIntersection(out intersectionPoint, inputSegment, demSegment))
{
segmentPointsWithDEMPoints.Add(intersectionPoint);
}
}
}
else
{
// No DEM coverage
segmentPointsWithDEMPoints = new List <GeoPoint>(2);
}
// add start and/or end point
if (returnStartPoint)
{
segmentPointsWithDEMPoints.Add(inputSegment.Start);
}
if (returnEndPoind)
{
segmentPointsWithDEMPoints.Add(inputSegment.End);
}
// sort points in segment order
//
segmentPointsWithDEMPoints.Sort(new DistanceFromPointComparer(new GeoPoint(startLat, startLon)));
return(segmentPointsWithDEMPoints);
}
