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: cg...@graytechsoftware.com Date:
2020-05-14 5:42 PM (GMT-04:00) To: qgis-user@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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