Viewshed
Given a map that contains a raster image layer with heights in pixel values and also a vector drawing layer that provides the locations and heights of observers as points, the Viewshed template computes viewsheds, that is, visibility of regions from the various observer points.
The template provides five different Output options, two of which report results by creating a new drawing, and three of which report results by creating a new image.
Output options that create a vector drawing:
- visible area from all - Create areas covering regions visible from all observer points.
- visible area from any - Create areas covering regions visible from any single observer point.
Output options that create a single channel, raster image:
- visible count - The value in each pixel reports the number of observer points from which this pixel is visible.
- visible level from all - The value in each pixel reports the vertical level this pixel must have to be visible from all observer points.
- visible level from any - The value in each pixel reports the vertical level this pixel must have to be visible from any single observer point.
The heights of observers can be taken from a numeric attribute field in the observer points table, or directly from Z geometry values for points (the default). If Z values are taken from a numeric field, they can be computed relative to the raster height (on by default) or taken as an absolute height.
There are options to specify refraction (the default is 0.13), minimum angle ( default -90 degrees), maximum angle (default 90 degrees), radius (default is 0 = no limit), and whether or not to use datum curvature (the default is not to use). Observer points can be restricted to only selected points.
Launch the template by choosing a Tile field and then double-clicking the Viewshed template. When the template launches we can specify options.
See the Viewsheds topic for a detailed discussion and examples.
Viewshed : visible area from all
Using values in the specified Channel of a raster image as heights of terrain, and given a drawing with points at the locations of observers, create a drawing with vector areas representing regions visible from all observer points.
Viewshed : visible area from any
Using values in the specified Channel of a raster image as heights of terrain, and given a drawing with points at the locations of observers, create a drawing with vector areas representing regions visible from any single observer point.
Viewshed : visible count
Using values in the specified Channel of a raster image as heights of terrain, and given a drawing with points at the locations of observers, create a drawing with vector areas reporting the number of observer points from which pixels in the area are visible.
Viewshed : visible level from all
Using values in the specified Channel of a raster image as heights of terrain, and given a drawing with points at the locations of observers, create a drawing with vector areas reporting the vertical level pixels in the area must have to be visible from all observer points.
Viewshed : visible level from any
Using values in the specified Channel of a raster image as heights of terrain, and given a drawing with points at the locations of observers, create a drawing with vector areas reporting the vertical level pixels in the area must have to be visible from any single observer point.