<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=utf-8"><meta name=Generator content="Microsoft Word 15 (filtered medium)"><style><!--
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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal>I’ve done what you described – select a point away from the edge and manually adjust the observer height. This does work. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I also tested negative observer height. If it is surrounded, the viewshed simply shows nothing (neighboring pixels only).<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>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.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thank you, Chris<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b>From:</b> kirk <kirk@nortekresources.com> <br><b>Sent:</b> Thursday, May 14, 2020 5:36 PM<br><b>To:</b> cgray@graytechsoftware.com; qgis-user@lists.osgeo.org<br><b>Subject:</b> Re: [Qgis-user] Viewshed >From Specific Elevation?<o:p></o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>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. <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div id="composer_signature"><div><p class=MsoNormal><span style='font-size:9.5pt;color:#575757'>Sent from my Samsung Galaxy smartphone.<o:p></o:p></span></p></div></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><div><p class=MsoNormal><span style='color:black'>-------- Original message --------<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='color:black'>From: <a href="mailto:cgray@graytechsoftware.com">cgray@graytechsoftware.com</a> <o:p></o:p></span></p></div><div><p class=MsoNormal><span style='color:black'>Date: 2020-05-14 5:42 PM (GMT-04:00) <o:p></o:p></span></p></div><div><p class=MsoNormal><span style='color:black'>To: <a href="mailto:qgis-user@lists.osgeo.org">qgis-user@lists.osgeo.org</a> <o:p></o:p></span></p></div><div><p class=MsoNormal><span style='color:black'>Subject: [Qgis-user] Viewshed From Specific Elevation? <o:p></o:p></span></p></div><div><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p></div></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>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. <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>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. <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>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. <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Thank you, Chris<o:p></o:p></p></div></div></body></html>