clipping a raster out of another raster ("doughnut" result) - using image analysis?

Question

Hi everyone-

I apologize for the fairly simple problem, but I've read several threads on the matter and even watched some videos, and I'm still not able to get what I want. What I'm trying to do is clip OUT a smaller raster from a larger one, leaving a hole where the smaller raster previously overlaid (leaving a "doughnut" shape, if you will). The only techniques I can find in ArcGIS 10 clip or mask the extent of the LARGER raster to the SMALLER one, so that I get the exact opposite result that I'm going for. I know there must be a fairly simple answer out there, but I'm getting really frustrated. I've read that the image analysis toolbar can be used, but I haven't been able to get it to work. Any help on this matter would be EXTREMELY appreciated, thanks.

Emma

EmmaYoung · Answer

Thanks, everyone!! I got it. Much appreciated!

GeospatialTechnology · Answer

Hi Emma, a quick and dirty way to do it would be to create a new .shp or feature class and then draw a big polygon that is bigger than the raster area you're looking at. You then want to draw a polygon representing the smaller area of raster you want to remove. Clip this smaller area out of the larger polygon. You'll have a hole in the bigger polygon where the the smaller polygon was and where you want the smaller area of raster to be removed. You can then use this to extract by mask as anything under the mask will be kept but the area where there is no polygon will be removed.

Luke_Pinner · Answer

In the raster calculator use an expression like below:Con(IsNull("little raster"), "big raster")

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Before running the tool, click the environments button and set Processing Extent to "Same as layer big raster".
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rastercalc.png