[GIS] Reclassify says: ‘Unique values cannot be obtained from raster, using values from dialog’

arcgis-10.2arcgis-desktoparcmaperrorreclassify

I am using ArcGIS 10.2. Whenever I reclassify a raster layer I get the following message:

Unique values cannot be obtained from raster, using values from dialog

This does not prevent from proceeding with the reclassification. I found that if I convert the data to integer prior to reclassification, I do not receive this message.

However, I do not want to convert all my data to integer, especially since I am using data which is represented by values of less than one, hence needing the additional step of multiplying the rasters by 1000 before integrating them.

What does this error message mean? Can I just ignore it? Does it affect the accuracy of the reclassifications?

Best Answer

From ESRI support: Increase the maximum number of unique values allowed in a raster attribute table

Try setting the maximum number of unique values to one greater than the number of cells in the raster dataset; I suspect it will go away.

In ArcMap or ArcCatalog, click Tools > Options. (In ArcGIS 10, click Customize > ArcMap Options.)
Click the Raster tab.
Select the sub-tab named Raster Attribute Table. (In ArcGIS 10, it is on the Raster Dataset sub-tab.)
Increase the maximum number.

I do not think it alters the reclass one iota. Just an annoyance.

Related Solutions

[GIS] Reclassify raster values of 9999 to NoData, leaving all other values alone, in ArcGIS Desktop

you can do this with arcpy, if you want. In this code, any input cell with a value 9999 will be set to NoData in the output raster, and the remaining cells will retain their original value.

import arcpy
from arcpy import env
from arcpy.sa import *
env.workspace = "C:/sapyexamples/data"
outSetNull = SetNull("elevation", "elevation", "VALUE = 9999")
outSetNull.save("C:/sapyexamples/output/outsetnull")

you can read Conditional evaluation with Con and Set Null (Spatial Analyst) from ArcGIS Resource Center...

Syntax
SetNull (in_conditional_raster, in_false_raster_or_constant, {where_clause})

SetNull

i hope it helps you...

[GIS] Reclassifying float raster using QGIS

yes, r.reclass is for reclassing thematic rasters, like the Corine Land Cover. It will work for your data, but the routine will cast the float numbers to integers before doing the reclass, so it might lead to unexpected results.

What you are looking for is r.recode

The rules are defined in many formats, one of those is the following:

old_low:old_high:new_val (i.e. new_high == new_low)

So, based on your question the rules should be something along this lines:

rules.txt

1:1000:1
1000:2000:2
2000:3000:3
3000:4000:4
4000:5000:5
5000:6000:6
6000:7000:7
7000:8000:8
8000:9000:9
9000:*:10

So the command should be like this:

r.recode input=oldmap output=newmap rules="/path/to/rules.txt"

Afterwards you can use the r.reclass module for the newmap you created.

Best Answer

Related Solutions

[GIS] Reclassify raster values of 9999 to NoData, leaving all other values alone, in ArcGIS Desktop

[GIS] Reclassifying float raster using QGIS

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