Project Raster Unit Conversion Issue

Question

Hello!

I am trying to use the Project Raster tool to convert a raster in the WGS 1984 Web Mercator (auxiliary sphere) projection to the NAD 1983 StatePlane Texas S Central FIPS 4204 (US Feet) projection (which are also different GCS).

The input raster is a road elevation DEM in meters, and I need the output in feet. When I use the Project Raster tool, the cell values are not converted from meters to feet. Why is that? Do I have to use the raster calculator following projection into the new PCS/GCS to convert the cell values from meters to feet?

JonathanLebowitz · Answer

Thank you for clarifying that. The Project Raster tool will only modify the pixel values based on the resampling technique (output will be minimal as you have observed). They will not change according to a transformation, such as the meters to feet vertical transformation. The raster calculator solution noted above will indeed allow you to convert the pixel values from meters to feet but note that 0.3048 Meter is equal to 1 International Foot. For PCS NAD 1983 StatePlane Texas S Central FIPS 4204 (US Feet), 1 US Survey Foot is equal to 1200/3937 meter (https://geodesy.noaa.gov/library/pdfs/NOAA_Manual_NOS_NGS_0005.pdf).

TrinityShuler02 · Answer

The pixel values represent elevation in meters. I used the default environment settings to project the raster, but the units were not converted from meters to feet. For example, when I click on the WGS projected raster, the value is 191.82, and when I click on the raster converted to NAD the value is 191.74, telling me the Convert Units default did not convert my units from meters to feet. If it did, the value would be about 638.9 ft. So, I had to follow up the projection with the convert units methodology posted by Dan Patterson.

JonathanLebowitz · Answer

Hello. What are the pixel values in your raster representing? X? Y? In the Project Raster tool, pixel value changes are determined by the resampling technique, not the linear units of the output coordinate system. The units of the cell sizes in the raster, however, would be determined based on the Cell Size Projection Method environment setting. The Convert units option is the default.