[Qgis-user] Viewshed From Specific Elevation?

[kirk]

You could try converting the first lidar returns to a raster layer and using a negative elevation observer value or select point that is one or 3 pixels away from the edge of the roof.  I am not sure if the negative observer height will work but it may.  If you need to remove obstructions, you can create a mask and recalculate the elevations if the obsructions below the observer height and rerun the viewshed. Sent from my Samsung Galaxy smartphone.
-------- Original message --------From: cgray at graytechsoftware.com Date: 2020-05-14  5:42 PM  (GMT-04:00) To: qgis-user at lists.osgeo.org Subject: [Qgis-user] Viewshed From Specific Elevation? I am attempting to test viewsheds from multiple heights below the roofline of particular buildings. I have been identifying viewing positions from directly from LiDAR data, but I cannot find a way to use absolute values for elevation.  The build-in visibility analysis seems to always use the raster elevation value plus the relative observer height.  I would like to use an absolute Z value, and have some immediate zone that is ignored (i.e., ignore the first 2m of obstructions) so that a viewpoint that might be lower than the raster elevation value can get outside of a building.  Is there a plugin or alternative visibility analysis tool that can do this? I was able to get it to work in Manifold Viewer, but I would like to keep the workflow within QGIS if possible.  Thank you, Chris
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