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Question about Z value and "OFFSETA" in Viewshed

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05-05-2022 02:42 PM
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MattTarkington1
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Occasional Contributor
‎05-05-2022 02:42 PM

I'm doing a viewshed study to be published online for sharing. My workflow is: Pull in DEM, Drop Points for Observers, Interpolate shape on observer points, Adjust Z (for the height of antenna, in field "OFFSETA") for observer points (this is so it looks better when published online), Run Viewshed (OFFSETA for antenna height).

 

My question is: Does the viewshed use the z value in the point for the analysis. Am I accidentally using the offset height twice by adjusting z value and using OFFSETA in the analysis?

 

Thanks,

 

Matt

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Robert_LeClair
by Esri Notable Contributor
Esri Notable Contributor
‎05-06-2022 08:19 AM

With viewshed analysis, if you don't use an OFFSETA in the GP tool parameter OR have it as an attribute field in your feature class, then the tools use the DEFAULT value for OFFSETA which is 1.  Could be 1 foot, 1 meter - depends on your coordinate system.  So no, you're doubling the height - essentially 1 unit of measure above the surface.

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Robert_LeClair
by Esri Notable Contributor
Esri Notable Contributor
‎05-06-2022 08:19 AM

With viewshed analysis, if you don't use an OFFSETA in the GP tool parameter OR have it as an attribute field in your feature class, then the tools use the DEFAULT value for OFFSETA which is 1.  Could be 1 foot, 1 meter - depends on your coordinate system.  So no, you're doubling the height - essentially 1 unit of measure above the surface.