TGIS_Viewshed class

DK for .NET | TatukGIS.NDK.TGIS_Viewshed | Classes | Constructors | Methods | Properties | Events

Viewshed, above-ground-level (AGL), and Fresnel zone clearance generator.

Available also on: Delphi | Java | ActiveX | Python.

// C#
public class TGIS_Viewshed : TGIS_BaseObjectDisposable
{
}

' VisualBasic
Public Class TGIS_Viewshed
  Inherits TGIS_BaseObjectDisposable
End Class

// Oxygene
type
  TGIS_Viewshed = public class( TGIS_BaseObjectDisposable )
  end;

→ TGIS_BaseObjectDisposable

PURPOSE: Performs terrain-based visibility analysis from point observers or transmitters using a DEM and prepared raster output layers.

BEHAVIOR: Generates viewshed rasters, optional AGL rasters, and Fresnel zone clearance maps. Observer or transmitter elevations can be taken from Z, M, ZM, the DEM, or the DEM plus M, and can be additionally adjusted by fixed and field-based offsets. Up to 50 point features from the observer layer are used. OpenCL acceleration is available for viewshed generation only; AGL and Fresnel zone clearance are always computed on the CPU. For best performance, use ViewshedOutput = Visibility and leave AboveGroundLevelLayer unset.

USAGE: Configure analysis properties and prepared layers, then call a generation method.

viewshed = TGIS_Viewshed()
viewshed.TerrainLayer = demLayer
viewshed.ObserversLayer = observerLayer
viewshed.OutputLayer = outputLayer
viewshed.Generate()

CONSTRAINTS: Output raster layers must be constructed before generation. AboveGroundLevelLayer must match OutputLayer extent, coordinate system, and resolution. The observer or transmitter layer is expected to contain point shapes only.

A viewshed is the area of visibility of an observed object(s), or, conversely, an area that can be seen from an observer location(s). For more information see this article on Wikipedia.

We provide a way to perform common analysis:

• Viewshed
  Creates a pixel layer where pixel values represent the number of observers visible from a particular location. This analysis can be used in two common scenarios:
  • Visibility (binary) case - values greater than or equal to 1 mean that a location is visible by at least one observer.
  • Frequency case - pixel value represents the number of observers visible from a particular location.
• Above-Ground-Level
  Creates a pixel layer where pixel values indicate the minimum height that must be added to a non-visible cell to make it visible by at least one observer.

Sample results:

Visibility	Frequency	Above-Ground-Level
green - visible area	color ramp red→green where: red - one observer visible green - all observers visible	color ramp green→red where: green - 1m red - 1440m

Analyses for polygonal areas (e.g., an exact city charter) can be done using the following steps:

1. Uerform standard viewshed analysis for are which fully encompass a charter.
2. Use TGIS_LayerPixel.Loop query for area covered by polygon on the result of the previous step. See how to do this in SimpleEdit sample.

Analyses for lines (e.g., how many times an observer is visible from a given segment of road) can be done using the following steps:

1. Perform standard viewshed analysis for the area which encompassing the segment of road.
2. Use TGIS_LayerPixel.Loop to query for terrain profile on the result of the previous step. See how to do this in SimpleEdit sample.

Result of Generate method is a TGIS_LayerPixel. Polygonal shapes covering visibility areas can be generated from the TGIS_LayerPixel using TGIS_ContourGenerator.

• Viewshed sample