GetLineOfSight Method (SurfaceLayer)

In This Topic

Performs a line of sight analysis for an observer and target point on the surface. Determines if the target point is visible from a given observer point. This method requires a 3D Analyst license. This method must be called on the MCT. Use QueuedTask.Run.

Syntax

C#
Visual Basic (Declaration)

public virtual LineOfSightResult GetLineOfSight( 
   LineOfSightParams lineOfSightParams
)

Public Overridable Function GetLineOfSight( _
   ByVal lineOfSightParams As LineOfSightParams _
) As LineOfSightResult

Parameters

lineOfSightParams: The object which contains all input values.

Return Value

A LineOfSightResult instance.

Exceptions

Exception	Description
System.ArgumentNullException	lineOfSightParams cannot be null.
System.InvalidOperationException	GetLineOfSight is only supported on TIN layers.
ArcGIS.Core.Licensing.Exceptions.LicenseException	A 3D Analyst license is required.
System.ArgumentException	The set of parameters is invalid for this surface. See CanGetLineOfSight.
MappingException	An exception occurred within the Line of Sight calculation.
ArcGIS.Core.CalledOnWrongThreadException	This method or property must be called within the lambda passed to QueuedTask.Run.

Remarks

See the following links for more information about Line of Sight analysis - https://pro.arcgis.com/en/pro-app/latest/tool-reference/3d-analyst/line-of-sight.htm and https://pro.arcgis.com/en/pro-app/latest/tool-reference/3d-analyst/how-line-of-sight-works.htm. Note that the geoprocessing tool uses a feature class of lines for the observer and target inputs whereas this method performs the calculation on a single pair of MapPoints only.

Use CanGetLineOfSight to determine if the set of input parameters is valid prior to calling this method.

The elevation of the observer point (let's call it observerZ) is derived as follows. If you provide a Z-aware (3D) observer point, observerZ will be set to its Z value; if you provide a 2D observer point, then observerZ will be set to the Z value of the surface at the XY of the observer point. If you specify an observer height offset, it will be added to observerZ. Similarly with the target point for calculating targetZ.

GetLineOfSight doesn't always produce all possible results. Internally the function generates an imaginary straight 3D line (the sight line) from the observer point (at observerZ) to the target point (at targetZ). It then interpolates (drapes) this line onto the surface, creating an imaginary profile line. The typical results consist of a "visible" line (possibly a multipart line) representing the portion of the profile line which is visible from the observer point (at observerZ), and an "invisible" line (possibly a multipart line) representing the portion of the profile line which is not visible from the observer point (at observerZ). If the sight line intersects the surface at least once, then an obstruction point is created at the first intersection point which is closest to the observer point.The obstruction point, if one is created, will always lie along the profile line, but will typically not occur at the end of the first visible line part.

Example

Get Line of Sight

var losParams = new LineOfSightParams();
losParams.ObserverPoint = observerPoint;
losParams.TargetPoint = targetPoint;

// add offsets if appropriate
// losParams.ObserverHeightOffset = observerOffset;
// losParams.TargetHeightOffset = targerOffset;

// set output spatial reference
losParams.OutputSpatialReference = MapView.Active.Map.SpatialReference;

LineOfSightResult results = null;
try
{
  if (tinLayer.CanGetLineOfSight(losParams))
    results = tinLayer.GetLineOfSight(losParams);
}
catch (Exception ex)
{
  // log exception message
}

if (results != null)
{
  bool targetIsVisibleFromObserverPoint = results.IsTargetVisibleFromObserverPoint;
  //These properties are not used. They will always be false
  // results.IsTargetVisibleFromVisibleLine;
  // results.IsTargetVisibleFromInvisibleLine;


  if (results.VisibleLine != null)
    MapView.Active.AddOverlay(results.VisibleLine, visibleLineSymbol.MakeSymbolReference());
  if (results.InvisibleLine != null)
    MapView.Active.AddOverlay(results.VisibleLine, invisibleLineSymbol.MakeSymbolReference());
  if (results.ObstructionPoint != null)
    MapView.Active.AddOverlay(results.ObstructionPoint, obstructionPointSymbol.MakeSymbolReference());
}

Requirements

Target Platforms: Windows 11, Windows 10

ArcGIS Pro version: 3.2 or higher.

Reference

SurfaceLayer Class
SurfaceLayer Members

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