Combine tool Problems

[MitchelMoynihan]

Hi Everyone,
I'm having an issue when attempting to combine 2 rasters. The tool runs and pops a new layer into my T.O.C window but the attribute table in the new layer is completely empty. No new raster appears in the map window..I have no idea why this is happening as the format for both rasters is identical(projection, bands, pixel depth etc). The only theory I have so far is that because I used the combine tool to create the 2 rasters I now need to combine again and maybe you can only use the tool once on a raster??

Any insight would be greatly appreciated as this is becoming really frustrating given that the tool worked fine to create these rasters in the first place.

Thanks.

[GayathriAlallasundaram]

Hi,

Open a new ArcMap and bring the two rasters and try using the Combinatorial Or tool (Spatial Analyst> Math > logical) which is similar  to the Combine tool.

-Gayu

[MitchelMoynihan]

Hi Gayu,
Thank you for the prompt reply but for the purposes of this project I need to be able to keep the values from both rasters hence using the combine tool. I had looked at the combinatorial tools but their outputs are not what I am looking for..Any other alternatives you could suggest?

Thanks
Mitch.

[EricRice]

Mitch,

How many unique combinations would you guess you have?  Per the Usage tips within the Combine tool's documentation it says the following:

"For formats other than ESRI GRID, by default, the output raster from this tool can only have a maximum of 65536 unique values.

You can increase this number by changing a setting in ArcGIS. On the Main menu, select Customize > ArcMap Options.  In the ArcMap Options dialog box, click on the Raster tab and modify the Maximum number of unique values to render field to an appropriate value."

If there are more than 65536, an attribute table will not automatically be built.

-Eric

[MitchelMoynihan]

Hi Eric,
I tried your recommendation but no luck. I went as far as 1,000,000 unique values to render but it still didn't create an attribute table or appear in my map window. The 2rasters I am trying to combine have 5 and 8 unique values(classes) respectively so I think I should be well within the default allowed amount. Ive also tried removing any excess fields from the attribute tables of the rasters so as to leave only integer fields and I've conversely added integer value coded fields to see it that works but also to no avail. I've tried extracting single classes from each raster and attempted to combine those but that doesn't work either!.. Now I'm thinking I have a corrupt file maybe? (last ditch justifiaction I know!!)

Any more input would be appreciated as it'd be great to get this resolved before the weekend..

Mitch.

[EricRice]

Hi Mitch,

I've tested ArcGIS 10.0 sp3 and ArcGIS 10.1 Beta 2 and both are giving me the expected result when running the Combine tool.  What version are you using?  I would suggest contact Esri Support.

Eric

[MitchelMoynihan]

Hi Eric,
Just wanted to post a reply here for anyone who ran into similar issues. Turns out one of my input rasters had lost its projection from some earlier work I had carried out on it. When I discovered this I couldn't believe I had missed that as I had checked the source tab over and over looking for a clue for what was wrong!...*For shame*:rolleyes:....I guess the moral is always check you basics first before looking for the difficult answer!