I'm looking for a simple way to replace the value field in GRID format with values that I have in a csv. It would be much like doing a join, where the GRID and the csv have a FEATUREID and then getting a field value from the joined table to replace or to be displayed in the symbology, or to put it another way, these new values will be represented in the histogram for this raster? I am using arcMap to display the raster and would like the histogram to be based on a column other than the VALUE column.
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have you tried join by attributes then calculate field? I assume your GRID has attributes built. Are you trying to update the raster cell values or the RAT definitions?– Michael StimsonCommented Aug 28, 2015 at 0:01
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update the raster cell values. This may work, I'll have to build a raster catalog first– rickDCommented Aug 28, 2015 at 0:08
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The value that is stored by the raster can't be changed directly using field calculator but the fields in the RAT can be... so long as all the values change at the same time. A raster attribute table is a lookup from values in the raster, each cell value is represented by a row in the table, as long as the value in the raster doesn't change the values in the table can be modified as any other table.– Michael StimsonCommented Aug 28, 2015 at 0:15
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Welcome to GIS SE! As a new user be sure to take the Tour. Would you be able to edit your question to let us know what GIS software you are using to try and do this, please?– PolyGeo ♦Commented Aug 28, 2015 at 0:20
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1 Answer
You need to reclassify the raster. To query by the original Grid value you can either use conditional statements in Raster Calculator or ArcPy or just look up the value in the CSV, of course.
In ArcMap you need Spatial Analyst Extension for this. If you do not have it and cannot afford it then you can try QGIS. If your reclassification is simple then use Reclassify. However, the fact that you have a CSV suggests that you might be better off with Reclass By Table. Your CSV forms the basis of your remap table. The remap table is used as a look-up-table to create a second raster whose values will be the field value (in your case) that corresponds to the featureid in the original raster. In this instance, reclassification can be considered somewhat analogous to the results of a join.
answered Aug 28, 2015 at 6:08
