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

[EmmaYoung]

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

[JakeSkinner]

Hi Emma,

You can do this if you create a Mosaic Dataset from you imagery.  Once you have a mosaic dataset, you can apply the Clip function (right-click on mosaic dataset in catalog window > Properties > Function tab).  With this function you have the option to clip using 'Inside' for the type and it will remove the pixels under the clipping geometry.

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[EmmaYoung]

Do you mean "Create mosaic Dataset" in Data management? I went ahead and tried that, added my raster to the mosaic, but I'm not seeing the properties as displayed in your reply... any idea why? Thanks.


Edit: I should note that the raster I'm trying to clip is classified into four different cover types (not sure if that makes any difference). It seems like adding the file into a mosaic in a .gdb makes it all one value, which I'm trying to avoid. I read something about converting the file to a polygon and then converting that to graphics, and exporting the data and using the graphics to clip it? Would that work?

[Luke_Pinner]

In the raster calculator use an expression like below:

Con(IsNull("little raster"), "big raster")

.

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

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.

[EmmaYoung]

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