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clip hole in raster

RickCheney

For example, if I have a raster layer of Digital Elevation which represents the United States and I want to keep everything except the state of Texas. I have a vector layer polygon of the state of Texas which I hope can be used to clip or mask or intersect the raster data.

How do I get the raster DEM layer with an area cutout or missing where Texas was?

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IanHageman

Here are the steps... Penny Vossler has it correct.

1. Create a vector polygon of the entire US (including Texas).

2. Use the "Erase" tool to clip out (erase) Texas from the US shapefile. Now you will have a polygon of the US with Texas removed.

3. Use the Extract By Mask tool and have the DEM as your input raster and the new vector shapefile of the US (with Texas erased) as the other input.

4. You will now have a DEM with everything but Texas.

All comments

RickCheney

The reason I am marking this answer as correct is because it provides step-by-step instructions for someone searching this forum with a similar question.. The original answer was supplied by Darren Weins and is also the correct answer.

There are many ways to achieve the same result and many correct answers, anyone with a similar task can choose which method is best for them.

Thank You, all of you who helped me along this steep learning curve.

DarrenWiens2

Was this not sufficiently answered two days ago?

IanHageman

Here are the steps... Penny Vossler has it correct.

1. Create a vector polygon of the entire US (including Texas).

2. Use the "Erase" tool to clip out (erase) Texas from the US shapefile. Now you will have a polygon of the US with Texas removed.

3. Use the Extract By Mask tool and have the DEM as your input raster and the new vector shapefile of the US (with Texas erased) as the other input.

4. You will now have a DEM with everything but Texas.

RickCheney

It seemed like when I tried that I always ended up with Texas instead of everything except Texas. ExtractByMask worked perfectly, it extracted (or clipped) everything from the polygon except the data that represented Texas, it extracted a raster polygon with a hole where Texas was.

PennyVossler

I may be oversimplifying here, but it seems to me you could clip Texas out of the US map, then use this US-without-Texas as the input to clip the DEM.

PatIampietro

Another advantage of ExtractByMask over Clip and the like is that it returns a raster with the minimum rectangular footprint of the extraction fetaure(s) rather than that of the original raster to be clipped, with extraneous null cells everywhere outside the clip feature(s).

RickCheney

Thank you, all of you, for the help. I'm still a newbie and a bit intimidated by some solutions that seem complex but I am learning so much.

RickCheney

ExtractByMask worked! I used the Raster Elevation data for the input raster and used a vector that for this example represents the US with a hole where Texas would be for the Feature Mask data.

DarrenWiens2

Yes, either of those would work, although the OP says he only has geometry for Texas. Either way, the take-home message is: don't bother with Extract by Polygon if Extract by Mask will work.

XanderBakker

The advantage of ExtractByMask is that it allows a featurelayer as input and doesn't require a list of points that forms a polygon. However, in combination with Set Null or Con I would rather rasterize the polygons and use the Con statement to obtain the desired result.

Thinking again... what if you do use the ExtractByMask tool and use you states, but you select Texas and invert the selection (everything selected exact Texas). Wouldn't that generate the yield the desired output?

I'm gonna give it a try and will report back later...

DarrenWiens2

I don't see any mention of Extract by Mask, which seems to me the tool to use, to create an output that you can feed into Set Null (or Con) to remove the unwanted parts of the original raster.

RickCheney

Thanks, it looks like this tool is going to work. I got the tool setup and I tried using it. I got an error the first time but I will continue testing and maybe tweaking and see if I can get it to work. Thanks again.

XanderBakker

I find it strange that the user needs to specify the coordinates as a list of arcpy.Points() in the Extract by Polygon—Help | ArcGIS for Desktop tool. Not very user friendly I would say.

Attached a sample toolbox that you can extract to a folder on you disk and test.

The result will be something like this:

It will use the (first) selected polygon for the erase.

The code used is:

def main():
    import arcpy

    # parameters
    ras = arcpy.GetParameter(0)
    fc = arcpy.GetParameter(1)
    method = "OUTSIDE"
    ras_out = arcpy.GetParameterAsText(2)

    # get first polygon of fc
    polygon = arcpy.da.SearchCursor(fc, ('SHAPE@')).next()[0]

    # create list of points
    points = [pnt for pnt in polygon.getPart(0)]

    # Check out the ArcGIS Spatial Analyst extension license
    arcpy.CheckOutExtension("Spatial")

    # Execute ExtractByPolygon and save result
    result = arcpy.sa.ExtractByPolygon(ras, points, method)
    result.save(ras_out)

if __name__ == '__main__':
    main()

Note; it has't been tested thoroughly, and may crash when using a complex geometry.

EraseRaster.zip

n202722.pdf

RickCheney

I was only using the US map and the state of Texas as an example, but I will look into Making a Mosaic Layer

RickCheney

The solution in the Erase but for raster thread is to use Raster Calculator but as far as I can see the Raster Calculator uses only Raster data and I don't have raster data for the shape that I what to cut out. Maybe I can convert my vector area into raster and then use the Raster Calculator.

WesMiller

Have you thought about Clip—Help | ArcGIS for Desktop each state then Make Mosaic Layer—Help | ArcGIS for Desktop them back together minus Texas?

RebeccaStrauch__GISP

you may want to see if this works for you Erase but for raster

RickCheney

It looks like the Extract by Polygon only accepts X Y coordinates for the Polygon that represents Texas, if I was extracting or masking a rectangle the X Y coordinates would be easy but I'm not sure how to specify a shape as complex and the state of Texas with X Y coordinates.

DanPatterson_Retired

keep outside Extract by Polygon—Help | ArcGIS for Desktop

RickCheney

I can clip the raster data to get the state of Texas but not the United States without Texas.

WesMiller

I've never clipped a raster with a donut hole but you can clip a raster based on geometry with Clip—Help | ArcGIS for Desktop

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