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Extending an existing raster extent.

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04-14-2010 06:34 PM
CedricWannaz
by
New Contributor II
‎04-14-2010 06:34 PM
Dear all,

     If have a raster which covers part of the globe (say [-180,180] longitude and [-53, 85] latitude), that I want to use in map algebra computations with other rasters that are global. For the reduced raster not to reduce the extent of the output of these computations, it seems to me that I have to replace its NoData pixels with values, as well as to extend it so it covers the whole globe.

    I can reclassify the NoData (to 0 or to the global average), but I still have a reduced extent. I created a constant value raster that covers the globe and I was hoping to find a way to combine them, but I have not been very successful so far.

    Could anybody tell me how to proceed (using the toolbox if possible, and not "edition by hand")?


Thank you and best regards,

Cedric
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10 Replies
DesmondFoley
by
New Contributor
‎07-29-2016 03:34 AM

!@I had a similar problem with building out presence/absence (0/1) rasters to the same extent as a larger raster that I wanted to include in a Spatial Analyst Tools>Local>Combine analysis on, so after a lot of angst, came up with the following solution:

  1. Set data frame to WGS84 and correct extent using View>Data frame Properties>Extent>Fixed Extent (enter values). Clip Options>Check Clip to shape >Specify shape>Custom Extent (enter desired values)
  2. Created a graphic rectangle to the dimensions of raster with desired extent then converted to feature.
  3. Used this in Data Management>Raster>Raster Properties>Calculate statistics to prepare the smaller area raster for reclassifying.
  4. Reclassified (Spatial Analyst Tools>Reclass>Reclassify) Nodata as 0, Absence as 1, and Presence as 2.
  5. Then Clipped (Data Management>Raster>Raster processing>Clip) to raster containing desired extent ("Maintain clipping extent" Checked, which adjusts the number of columns and rows and resample pixels so as to exactly match the clipping extent specified), which will populate the pixels out to the desired extent with NoData values (you can visualize them by coloring NoData in layer properties).
  6. Then reclassify NoData and 1 to 0, and 2 to 1 to get a presence/absence raster of desired extent.
  7. Then export as tif (you can check in Property the extent is correct before punching the save button)

Maybe not all the steps are necessary for your situation but it worked for me. The key is the Calculate statistics bit, which is apparently necessary for a lot of analysis and reclassifying tasks especially those involving NoData cells.

Cheers

Des

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