topic Re: Update DEM or elevation data in 3D Mapping Questions

Update DEM or elevation data

BrianLomas — Thu, 04 Feb 2016 15:24:20 GMT

Is there a way to update/change a DEM file or some kind of elevation layer which I could use as a terrain? Basically, I have a DEM which has current elevation and I have a 3d multipatch polygon which represents a road that will be built. The road construction will change the landscape which is represented in the multipatch polygon. I need the elevation of the multipatch to be represented in the terrain as well as the surrounding areas current elevation. I hope that makes sense.

I included a picture and you can see where the road is intersected by the terrain. Thanks for the help.

Re: Update DEM or elevation data

JayantaPoddar — Fri, 05 Feb 2016 06:18:05 GMT

Hi Brian,

You could follow these steps.

1) Convert the multipatch to Raster. Keep the XY Resolution (cell size) same as that of the DEM.

Multipatch to Raster—Help | ArcGIS for Desktop

2)Now if I want to add up the value of "New_DEM" with the old "DEM" raster, I would use Raster calculator (Spatial Analyst) with a similar expression:

("New_DEM" + "DEM")

Re: Update DEM or elevation data

DanPatterson_Retired — Fri, 05 Feb 2016 08:29:00 GMT

if it is a visual thing, then you can simply use an offset from the dem once you done the draping it. This works quite well in most area when placing 2D vector data over DEM data

Re: Update DEM or elevation data

BrianLomas — Fri, 05 Feb 2016 17:14:29 GMT

I converted the multipatch to a raster. Is there a way to combine or merge the two rasters together, overriding the existing raster's info only where the new raster overlaps?

Re: Update DEM or elevation data

BrianLomas — Fri, 05 Feb 2016 17:17:04 GMT

This wouldn't solve my problem because if I raise the multipatch is would cause a gap b/w the raster and the road (multipatch) in some places. The multipatch is 3d as well. Thanks for the reply though.

Re: Update DEM or elevation data

JayantaPoddar — Fri, 05 Feb 2016 17:21:40 GMT

Did you try step 2 that I suggested?

Re: Update DEM or elevation data

BrianLomas — Fri, 05 Feb 2016 17:25:41 GMT

Yea, when I did that it seemed to only change the converted multipatch raster.

Re: Update DEM or elevation data

JayantaPoddar — Fri, 05 Feb 2016 17:29:48 GMT

Ok. Try this

Con(IsNull("New_DEM"),"DEM", ("DEM" + "New_DEM"))

Re: Update DEM or elevation data

DanPatterson_Retired — Fri, 05 Feb 2016 17:42:37 GMT

You have to ensure that the analysis extent is the same... You can use the Con—Help | ArcGIS for Desktop

Re: Update DEM or elevation data

DanPatterson_Retired — Fri, 05 Feb 2016 17:55:21 GMT

Another way...

for all steps set using tools in arctoolbox, set the analysis extent to be of the largest raster,
set the snap raster to it, and the cell size as well
export the smaller raster to a new copy (right click, on the layer, data export) which will have the larger extent setting the nodata value to zero
Add them together

Re: Update DEM or elevation data

BrianLomas — Fri, 05 Feb 2016 18:37:46 GMT

I ran Con(IsNull("New_DEM"),"DEM", ("DEM" + "New_DEM")) first then I tried changing the extent and running it again, both gave me the same result (pic attached). I'm probably making this harder than it really is. Thanks for your time and patience.

Re: Update DEM or elevation data

DanPatterson_Retired — Fri, 05 Feb 2016 22:02:50 GMT

I am assuming it looks fine if looked at in 2D? Just the patch area itself? in otherwords without the DEM. They are in the same Z units? If a scaling factor was applied, they are both the same? That is why I initially thought it looked like the feature was being 'clipped' when it was draped over the surface. In such cases, I applied a small offset and/or extrusion for visual purposes. So in short.. make sure it is indeed continuous in 2D and that all the data got converted to data etc

Re: Update DEM or elevation data

BrianLomas — Thu, 11 Feb 2016 14:43:48 GMT

I started from scratch by matching scales between the two files, then matched projections, then used the "mosaic to new raster" tool; this seemed to work. Thanks a lot for pointing me to in the right direction guys, you were a big help.