topic Re: elevation from colormap in ArcGIS Pro Questions

elevation from colormap

teakplantation — Fri, 29 Mar 2024 15:37:48 GMT

I have an old scanned map with includes elevation contours as well as elevation values colored according to colormap (similar to the example map below).

What I try to achieve is to assign a specific elevation to each color and then subsequently populate the entire map with the corresponding elevation values; so in essence I want to recreate the map from the colors instead of digitizing the contours by hand.

Any suggestions what ArcGIS Pro tool has such a capability?

Re: elevation from colormap

BobBooth1 — Mon, 01 Apr 2024 14:52:56 GMT

You would probably do better to use existing ArcGIS Online services, such as:

https://www.arcgis.com/home/item.html?id=51ca3ce6a16d4080ad955dacd6dd2fe2

https://www.esri.com/arcgis-blog/products/arcgis-living-atlas/announcements/high-resolution-data-updates-to-living-atlas-world-elevation-layers-and-tools-december-2022/

You can also download terrain data if you need a local copy, for example, search on SRTM.

Re: elevation from colormap

teakplantation — Tue, 02 Apr 2024 17:17:28 GMT

Hi Bob, unfortunately this doesn't work for me. The map is generated from an interpretation of a subsurface aquifer, hence not publicly accessible elevation data.

Re: elevation from colormap

BobBooth1 — Wed, 03 Apr 2024 14:45:23 GMT

Ah, I see. That's too bad.

I don't think there is a straightforward way to do this. You might create an array of points over the surface and sample the raster color values, then add a column for elevation and create a Python field calculation that would convert specific RGB values to match your estimated elevations for those colors.

You could use the Fishnet tool to create polygons, and then extract the centroids of those.

https://pro.arcgis.com/en/pro-app/3.1/tool-reference/data-management/how-create-fishnet-works.htm

https://support.esri.com/en-us/knowledge-base/how-to-find-the-centroid-of-polygons-using-calculate-ge-000021849

Then use Sample to get the raster values at those points:

https://pro.arcgis.com/en/pro-app/3.1/tool-reference/spatial-analyst/sample.htm

Add a field:

https://pro.arcgis.com/en/pro-app/latest/help/data/geodatabases/overview/create-modify-and-delete-fields.htm

Calculate new field values based on RGB values:

https://pro.arcgis.com/en/pro-app/3.1/tool-reference/data-management/calculate-field-examples.htm