dem-net/DEM.Net

Feature Request: Line of Sight calculation between two GeoPoints

rurounijones opened this issue · 5 comments

rurounijones commented

Is your feature request related to a problem? Please describe.

I just want to make sure that I am not missing something. My use-case is to have a Line-of-Sight calculation method to determine if two points (lat/lon/alt) on a WGS84 projection have line of sight between them. I am not sure if this is already possible using DEM.Net but wanted to check.

Describe the solution you'd like
A method along the lines of the following:

public bool HasLineOfSight(GeoPoint source, GeoPoint destination) {
  bool result = // Lots of complicated calculations
  return result
}

Ideally returns the result in less than 100ms for distances up to 100 nautical miles (assuming all tiles have been cached).

Describe alternatives you've considered

I have looked around the DEM.Net code to make sure I am not missing anything and that it is already possible without me realising it and I cannot see anything equivalent. I see there is already GeometryService.ParseGeoPointAsGeometryLine and the like which already provides a series of heights along a line which seems like it is half the work,

I have also looked around for example code / explanations but either I am using the wrong keywords or my complete lack of GIS experience is making me unable to understand the mathematics involved in such a calculation.

Additional context
None

xfischer commented

Hi @rurounijones, thanks for posting your issue.

Yes this is possible via 'Intervisibility' methods, which already exist, albeit not well documented.

See here for live example :
https://api.elevationapi.com/api/Elevation/intervisibility?latStart=43.5&lonStart=5.2&latEnd=43.6&lonEnd=5.5&dataSet=SRTM_GL3
With Plot : (https://api.elevationapi.com/api/Elevation/intervisibility/plot?latStart=43.5&lonStart=5.2&latEnd=43.6&lonEnd=5.5&dataSet=SRTM_GL3)
image

  • API is here :

DEM.Net/DEM.Net.Core/Services/Elevation/ElevationService.cs

Line 1086 in 945154c

public IntervisibilityReport GetIntervisibilityReport(GeoPoint source, GeoPoint target, DEMDataSet dataSet

  • Unit test (with sample) is here :

DEM.Net/DEM.Net.xUnit.Test/ElevationTests.cs

Lines 134 to 145 in 945154c

public void TestIntervisibility(string dataSetName, double latStart, double lonStart
, double latEnd, double lonEnd, double expectedObstacles)
{
DEMDataSet dataSet = DEMDataSet.RegisteredDatasets.FirstOrDefault(d => d.Name == dataSetName);
Assert.NotNull(dataSet);
IntervisibilityReport report = _elevationService.GetIntervisibilityReport(new GeoPoint(latStart, lonStart), new GeoPoint(latEnd, lonEnd), dataSet);
Assert.NotNull(report);
Assert.Equal(expectedObstacles, report.ObstacleCount, 0);
Assert.Equal(expectedObstacles, report.Metrics.Obstacles.Count, 0);
}

Let me know if you need further assistance.

rurounijones commented

Wow that was a quick reply! I did see the "Intervisbility" bit in the project description so was hoping. I edited my comment not expecting sucha quick response but does this take into account the curvature of the earth? e.g. in a WGS84 projection?

xfischer commented

No it does not take earth curvature into account, so this would be accurate enough for short distances.

I hope I'll get some time to fix it to enable spherical computations :)

rurounijones commented

Thank you very much for the info and examples. I will go away and give these a try.

For reference purposes: https://gitlab.com/overlord-bot/srs-bot/-/issues/30

xfischer commented

Found a nice reference here for future implementation : http://walter.bislins.ch/bloge/index.asp?page=Advanced+Earth+Curvature+Calculator