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ElevationMaskFromTerrain Method (TerrainProvider, Double, Double, Cartographic, Double, Double, Double, Boolean)

Computes elevation masks from the specified terrain provider along the provided azimuths.

Namespace:  AGI.Foundation.Terrain
Assembly:  AGI.Foundation.Models (in AGI.Foundation.Models.dll) Version: 24.2.419.0 (24.2.419.0)
Syntax
public static List<ElevationMask> FromTerrain(
	TerrainProvider provider,
	double minimumTerrainHeight,
	double maximumTerrainHeight,
	Cartographic observerPosition,
	double stepSize,
	double maximumSearchAngle,
	double[] azimuths,
	bool multithreadComputations
)

Parameters

provider
Type: AGI.Foundation.TerrainTerrainProvider
The source of terrain from which to compute the masks.
minimumTerrainHeight
Type: SystemDouble
The minimum height in meters that can be returned by the TerrainProvider's GetHeightRelativeToShape(Double, Double) method. Setting this value lower than necessary will not affect the results, but it will decrease performance. Setting it too high can cause incorrect results.
maximumTerrainHeight
Type: SystemDouble
The maximum height in meters that can be returned by the TerrainProvider's GetHeightRelativeToShape(Double, Double) method. Setting this value higher than necessary will not affect the results, but it will decrease performance. Setting it too low can cause incorrect results.
observerPosition
Type: AGI.Foundation.CoordinatesCartographic
The planetodetic position of the stationary observer at which the masks are computed.
stepSize
Type: SystemDouble
The size of the step along each azimuth ray, in radians.
maximumSearchAngle
Type: SystemDouble
The maximum angle, in radians, to move along each azimuth ray in constructing the masks.
azimuths
Type: SystemDouble
The azimuths, in radians, along which to compute the elevation masks.
multithreadComputations
Type: SystemBoolean
Indicates whether the computations should be multithreaded.

Return Value

Type: ListElevationMask
The elevation masks corresponding to each of the azimuths.
Exceptions
ExceptionCondition
ArgumentNullExceptionThrown if provider is .
ArgumentOutOfRangeExceptionThrown if azimuths is less than or equal to zero.
Remarks

This method works by casting a ray out from the observerPosition along a specified direction to determine the minimum elevation angle that is visible above the terrain in that direction. More specifically, the various distances at which the minimum elevation angle increases in that direction are determined.

stepSize is the distance between steps along the ray, in radians. A reasonable value for this parameter would sample approximately three times per terrain grid cell.

maximumSearchAngle is the maximum angle, in radians, to move along each ray. In other words, this parameter indicates the stopping point for sampling along the ray. A reasonable value will take into account the difference between the maximum and minimum heights of terrain provided by provider and potentially how close together the minimum and maximum heights are located.

Examples

The following example shows one way this value might be chosen:

C#
double approximateHeightOfMtEverest = 8850.0;
double semimajorAxisLength = WorldGeodeticSystem1984.Shape.SemimajorAxisLength;
double maximumSearchAngle = Math.Acos(semimajorAxisLength / (semimajorAxisLength + approximateHeightOfMtEverest));

See Also