Viewshed - point height

Question

Hi, Any help much appreciated. I am using Visibility (Spatial Analyst). I have an observer point and I want to know what was visible in the surrounding landscape. Therefore,

Input raster = DTM

Input point: this is the point (call it point A) from which I am making the observation

Observer offset: 1.75 (this adds 1.75m to point A, to model human observer height).

This works fine. However, I some other points in the map (points B and C) that I want to add a height value for to represent buildings (say 12 metres). I think this needs to go into the attribute table for those points, but I am not sure how I do this, under what field etc., to make the viewshed analysis take their height into account.

many thanks

NeilGodfrey · Answer

Thanks much appreciated - will have a go at that. Was on the wrong track with this.

DavidPike · Answer

You need to burn those buildings into your DEM.  Convert the building polygons into a raster (ensure you match the cell size and snap raster of your DEM).  Then Raster Calculator Ras1 + Ras2 (ensure NoData is set to 0)  Then run your analysis using this new raster.

NeilGodfrey · Answer

Many thanks, but I understand that OFFSET A adds the height values to the observation point. My observation height is human 1.75m. I want to add the height of another point to represent a building. Everything I try fails on this. The issue seems to be where do I put the OFFSET B height value in order to include the building in the analysis. I tried firstly, putting the OFFSET B height value into the same attribute table (different point) as the observer point, and added OFFSET B to Surface offset, but as the two points are in the same feature class it just did a viewshed from each. I tried use different features classes for the two points, and then the analysis cannot find offset B. I only want to add one building height and have it included in the analysis. Perhaps I need to simply add a field in the attribute table for height, but what would I call it to ensure it is considered?