[Qgis-user] Viewshed From Specific Elevation?

[cgray at graytechsoftware.com]

I’ve done what you described – select a point away from the edge and manually adjust the observer height. This does work. 

 

I also tested negative observer height. If it is surrounded, the viewshed simply shows nothing (neighboring pixels only).

 

However, I’m going to be doing 100+ points over multiple locations. Ideally, when I setup a viewshed point (including elevation), I can just run an analysis from that location and ignore the first 2m or so. I think manipulating every point will be cumbersome.

 

Thank you, Chris

 

 

From: kirk <kirk at nortekresources.com> 
Sent: Thursday, May 14, 2020 5:36 PM
To: cgray at graytechsoftware.com; qgis-user at lists.osgeo.org
Subject: Re: [Qgis-user] Viewshed From Specific Elevation?

 

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 <mailto:cgray at graytechsoftware.com>  

Date: 2020-05-14 5:42 PM (GMT-04:00) 

To: qgis-user at lists.osgeo.org <mailto: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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