Specify Geographic Transformation as user input in python script

Question

I have a script that includes the Project Raster process. The standard ArcToolbox tool dialog has an optional input to specify the Geographic Transformation. If it detects a datum transformation is needed between your input and output coordinate systems, it will automatically populate the drop-down list with relevant datum transformation options.

I would like to implement this type of parameter in my python script, but haven't been able to figure out how to go about it. The data type for this parameter is listed as "String" so I presume you could enter in the name for a transformation manually (i.e. "NAD_1927_To_NAD_1983_NADCON"), but it'd sure save a lot of trouble (who's going to remember the exact name?) if I could get the list to populate like on the standard tool.

Anyone ever do this successfully?

Many thanks!

KarenMiller · Answer

Thanks everyone for your responses! I had thought about using the tool validator, but it looks like you'd still have the problem intelligently populating the list. I agree, the easiest way would be to populate a value list filter with the most commonly used transformations - I simply was hoping I wouldn't have to guess what those will be in the future, in case something unusual comes up. And it looks like the improvements in 10.1 will do exactly what I want to do here. I suppose if one needs to use a transformation that isn't in my predefined list, they could just set it in the environment settings so it will run properly without crashing - that might be an acceptable work-around until 10.1 - whenever that is...

Thanks again- I'll give this a try and see how it goes!

LoganPugh · Answer

The easiest way to do it would be to define a parameter (in your script tool parameters tab) that is of type String and has a Value Filter consisting of the names of the common transformations you listed. That way they appear as a dropdown that the user can pick from and the value chosen will be used as the input to your script.

See Setting script tool parameters in the help.

Otherwise I believe you would need to use ArcObjects to do something more intelligent such as listing only those transformations that apply between the two coordinate systems. The method Mr. Prince listed above would certainly make that easily doable within Python at 10.1.

Also, there is a link to a list of all the transformations on this page: http://resources.arcgis.com/content/kbase?fa=articleShow&d=21327

DarrenWiens2 · Answer

Would using a Tool Validator work? I've never used one, but it seems like you could use it to populate your combobox.