Mosaic Dataset build footprint based on alpha band

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06-15-2021 12:41 AM
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MarkChilcott
Occasional Contributor III

Hi Peoples,

I have a number of ECW rasters that contain an alpha band that acts as a transparency mask.

I would like to calculate footprints for the rasters.  I can't see how to specify to use just the value of the alpha band to achieve this.  Anyone done this?  

https://pro.arcgis.com/en/pro-app/latest/help/data/imagery/raster-display-ribbon.htm

Cheers,

Mark

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GordonSumerling
Esri Contributor

Hello Mark,

Yes this can be achieved. I have utilised raster functions to do this. Usually the alpha channel is 0 & 255. 

So what you do is as follows:

  1. Use the raster function to Extract the Alphas channel from the image (Extract Bands)
  2. This will give you a single band image of 0 & 255
  3. Then use the GP tool Raster to Polygon.
  4. This will give you a vector layer of the image boundary and the image content.
  5. You can then filter the vector layer by either of the values.

Hopefully this is what you are after. You can even use this shape to replace the footprints in a Mosaic dataset

 

Cheers

Gordon

 

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2 Replies
GordonSumerling
Esri Contributor

Hello Mark,

Yes this can be achieved. I have utilised raster functions to do this. Usually the alpha channel is 0 & 255. 

So what you do is as follows:

  1. Use the raster function to Extract the Alphas channel from the image (Extract Bands)
  2. This will give you a single band image of 0 & 255
  3. Then use the GP tool Raster to Polygon.
  4. This will give you a vector layer of the image boundary and the image content.
  5. You can then filter the vector layer by either of the values.

Hopefully this is what you are after. You can even use this shape to replace the footprints in a Mosaic dataset

 

Cheers

Gordon

 

MarkChilcott
Occasional Contributor III

Thanks Gordon.  As I was using .ecw the Extract Bands gave a result that was not 0 or 1.  I got around this by doing a Reclass.  Using the GP Raster to Polygon on the reclassed raster gave the footprint.  I could then simplify and shrink as required.

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