topic Apply datum tranformation only if source datum is different than target in Python Questions

Apply datum tranformation only if source datum is different than target

ZacharyHart — Fri, 22 Oct 2021 19:49:07 GMT

I'm trying to create a simple evaluation within a script which does not restrict the spatial reference of the data, but the output is fixed: WGS 1983 Web Mercator Aux Sphere. All inputs will be projected data.

I want to project any input data to match the desired output projection, but I need to evaluate the datum of the input vs the output. .

Unfortunately, according to the documentation found here, this property (GCSName) is available only for geographic data. However:

Because a projected coordinate system is based on a geographic coordinate system, projected coordinate system properties can be accessed from a geographic coordinate system via the GCS property.

But the GCS property returns a spatial reference object for which I do not know how to format or parse parameters from to evaluate. Is there a way to do this? This will eventually be rolled-up into a script tool.

Any general tips on handling such a process would be greatly appreciated. I anticipate there will only be a handful of input PCS to deal with but it is entirely possible that there both NAD83 & WGS84 datums (3 feet matters for us in this case!).

Re: Apply datum tranformation only if source datum is different than target

DanPatterson — Fri, 22 Oct 2021 21:42:08 GMT

in_fc = r"C:\Git_Dan\npgeom_bak\Project_npg\npgeom.gdb\Ontario_singlepart" sr = arcpy.Describe(in_fc).spatialReference sr.name 'NAD_1983_Statistics_Canada_Lambert' sr.exportToString() 'PROJCS["NAD_1983_Statistics_Canada_Lambert", GEOGCS["GCS_North_American_1983", DATUM["D_North_American_1983", SPHEROID["GRS_1980",6378137.0,298.257222101]], PRIMEM["Greenwich",0.0], UNIT["Degree",0.0174532925199433]], PROJECTION["Lambert_Conformal_Conic"], PARAMETER["False_Easting",6200000.0], PARAMETER["False_Northing",3000000.0], PARAMETER["Central_Meridian",-91.86666666666666], PARAMETER["Standard_Parallel_1",49.0], PARAMETER["Standard_Parallel_2",77.0], PARAMETER["Latitude_Of_Origin",63.390675], UNIT["Meter",1.0]];-28455800 -28572600 10000;-100000 10000;-100000 10000;0.001;0.001;0.001;IsHighPrecision'

There are easier ways to get at the information, but every projected coordinate system has a root GCS and hence a datum associated with (lines 9 and 10). You just have to sift through the properties

SpatialReference—ArcGIS Pro | Documentation

Re: Apply datum tranformation only if source datum is different than target

ZacharyHart — Fri, 22 Oct 2021 21:54:40 GMT

Thanks Dan! That's the same doc I linked to as well. I'm able to generate the string, but are the items in the Spatial Reference object indexed so I can parse them out? Are they keyed? The documentation isn't very detailed.

Thanks again, you do so much for us!

Re: Apply datum tranformation only if source datum is different than target

DanPatterson — Sat, 23 Oct 2021 00:34:50 GMT

for my example

sr.GCS <geoprocessing spatial reference object at 0x243ed372af0> sr.GCS.name 'GCS_North_American_1983'

instead of parsing the whole string

Re: Apply datum tranformation only if source datum is different than target

ZacharyHart — Mon, 25 Oct 2021 12:55:17 GMT

that works, thanks!! i'm off to the races now.