topic Re: Raster without count field in Data Management Questions

Raster without count field

MartinaHepp — Mon, 12 Jul 2010 17:32:04 GMT

Hi!

I am working on an accuracy assessment of a vector map with a raster data set as reference data. I wanted to use the Hawth tool 'Thematic Raster Summary' to see how many pixels of each value underlay each polygon. That tool doesn't work, however, as my raster file lacks a count field! I didn't even know that was possible and I couldn't find a way to calculate it manually, either. Also, exporting the TIFF again (into a new TIFF or GRID e.g.) didn't help. Anyone able to help me out here? I am aware of the tool 'Clip raster by Polygon' as well, but the result is always highly erroneous in this case (big amount of NoData in the resulting map), so I figured a resulting dbf might work better...

Cheers,
Tina

Re: Raster without count field

DanPatterson_Retired — Mon, 12 Jul 2010 21:33:54 GMT

Did you convert it to an ESRI grid? Do you have a table at all? There are limits in displaying a table based upon the number of unique conditions and the range within the data set. If you don't have a table at all, then is it floating point data?
see
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009t00000009000000.htm
similar info exists for 9.x

Re: Raster without count field

MartinaHepp — Tue, 13 Jul 2010 16:46:14 GMT

Yes, I tried to convert it to a GRID-Filee, that didn't help.:( And it does have a table, it has an OID and a VALUE field (and some more), it just lacks the COUNT field...

Re: Raster without count field

DanPatterson_Retired — Tue, 13 Jul 2010 17:55:25 GMT

so you are confirming that it is an ESRI integer grid...how many classes? what is the range in values? Can you check the table properties?

Re: Raster without count field

MartinaHepp — Wed, 14 Jul 2010 17:25:39 GMT

@ Bill: Actually, every raster is supposed to have an OID field - at least that's what I understand from the ArcMap Help as well as Dan's link!? And if I convert it to integer, a lot of my values get lost.:(

@ Dan: I have 36 classes, but 256 entries (most of them NoData). The values range from 0 ot 256 like the OID, but only special entries have value. Are you familiar with the EOSD? That's what the table contains... So OID, Value, Red, Green and Blue. Every entry that has RGB values is part of these 36 classes. Does that make sense?

Re: Raster without count field

DanPatterson_Retired — Thu, 15 Jul 2010 13:45:53 GMT

provide me with the link to the file you downloaded, there are too many to guess which one. In arcmap 10, any tiff got converted to a grid stack and each individual grid has values ranging from 0-255 as would be expected.

Re: Raster without count field

MartinaHepp — Mon, 19 Jul 2010 18:17:25 GMT

So I finally got the link where the file is from: It's http://www.saforah.org/ and I am working on tile 084E! Hope that helps... What you write about the TIFFs in ArcMap 10 seems to be some part of an explanation... I myself am working on ArcMap 9.3, though, so the TIFF must have been exported from ArcMap 10!?

Cheers,
Tina

Re: Raster without count field

DanPatterson_Retired — Mon, 19 Jul 2010 19:19:20 GMT

Tina
exact data set! I can check on 9.3 and 10 but I need to know if you are using a classified file or one of those tiff's that is nothing more than a pretty picture (ie RGB bands). If it is the latter, then you will only get count data for the individual bands and not the classified data (ie urban landuse etc which has a certain RGB colour)

Re: Raster without count field

MartinaHepp — Mon, 19 Jul 2010 20:50:27 GMT

Thanks, Dan! I think I just got a huge step closer to solving my problem: Someone told me to open the *.pix-file of the EOSD and convert it into a GRID. The result looks good and the table has a COUNT-field, too!:) The thematic raster summary still doesn't work, though. But that might be because my PC is really slow right now and needs a re-format. I am going to try it on another one tomorrow and let you know.