Checking if two feature classes have same spatial reference using ArcPy

Question

Using ArcPy, how do you check if two feature classes have the same spatial reference?

Just checking if the two are equal doesn't work:

>>> import arcpy
>>> fc1 = r"C:\Users\e1b8\Desktop\E1B8\GIS_Stackexchange\data.gdb\test"
>>> sr1 = arcpy.Describe (fc1).spatialReference 
>>> sr2 = arcpy.Describe (fc1).spatialReference
>>> sr1 == sr2
False

factoryCode doesn't work, because custom projections don't have them.

>>> fc2 = r"C:\Users\e1b8\Desktop\E1B8\GIS_Stackexchange\data.gdb\customproj"
>>> sr2 = arcpy.Describe (fc2).spatialReference
>>> sr2.factoryCode
0

There's name, but names can be the same, but have different units:

>>> sr1 = arcpy.Describe (fc1).spatialReference
>>> sr2 = arcpy.Describe (fc2).spatialReference
>>> sr1.name
u'NAD_1983_UTM_Zone_10N'
>>> sr2.name
u'NAD_1983_UTM_Zone_10N'
>>> sr1.linearUnitCode
9003
>>> sr2.linearUnitCode
9001

So it gets a bit complicated. The best I've come up with is:

>>> def CompareSRs (inFc1, inFc2):
 sr1 = arcpy.Describe (inFc1).spatialReference
 sr2 = arcpy.Describe (inFc2).spatialReference
 if not sr1.name != sr2.name:
 return False
 srType = sr1.type
 if srType != sr2.type:
 return False
 if srType == "Geographic":
 return sr1.angularUnitCode == sr2.angularUnitCode
 return sr1.linearUnitCode == sr2.linearUnitCode

And I'm still not sure the above code is air tight.

Is there a better way?

• Aaron: This may be helpful: gis.stackexchange.com/q/50312/8104

Answer 1

Judging from comments, you might have it already :)

You could compare the Well-Known Text (WKT) descriptions of the spatial references.

sr1 = arcpy.Describe(dataset1).spatialReference
sr2 = arcpy.Describe(dataset2).spatialReference
sr1String = sr1.exportToString()
sr2String = sr2.exportToString()
matching = False
if sr1String == sr2String:
 # Exact string match
 matching = True
else:
 # difference
 pass

Answer 2

In case 2019, I had similar issues using ArcMap 10.3 and wanted to be as sure as possible as to whether projections matched. As in the above question/answers, you can get the spatial reference using arcpy.Describe(dataset).spatialReference. In a function library of mine, I then integrate this into a workflow, set-up to handle the comparison of 2 datasets.

The individual attributes of a geoprocessing spatial reference object are available here.

The following functions should help - feel free to use/modify of course. Worth checking what is omitted - some attributes of the spatial reference systems will be harmless if they don't match but that's up to you :)

import arcpy
def check_crs(dataset):
 """Return a coordinate reference system string
 Get coordinate reference system of dataset
 """
 crs = arcpy.Describe(dataset).spatialReference
 return(crs)
def assert_crs_attribs(dataset1, dataset2, strict=False): 
 """Returns Nothing
 Asserts equality of all attributes of the provided geoprocessing spatial reference objects.
 These are generated using arcpy.Describe(your_dataset).spatialReference.
 Attributes of spatial reference object: https://pro.arcgis.com/en/pro-app/arcpy/classes/spatialreference.htm
 dataset1 - a spatial dataset with projection info e.g. shp
 dataset2 - a spatial dataset with projection info e.g. shp
 strict - boolean - if True will compare every element (default: False)
 """
 crs1=check_crs(dataset1)
 crs2=check_crs(dataset2)
 try:
 # Consider these
 assert(crs1.name==crs2.name) # The name of the spatial reference.
 assert(crs1.PCSCode==crs2.PCSCode) # The projected coordinate system code.1 
 assert(crs1.PCSName==crs2.PCSName) # The projected coordinate system name.1 
 assert(crs1.azimuth==crs2.azimuth) # The azimuth of a projected coordinate system.1 
 assert(crs1.centralMeridian==crs2.centralMeridian) # The central meridian of a projected coordinate system.1 
 assert(crs1.centralMeridianInDegrees==crs2.centralMeridianInDegrees) # The central meridian (Lambda0) of a projected coordinate system in degrees.1 
 assert(crs1.centralParallel==crs2.centralParallel) # The central parallel of a projected coordinate system.1
 assert(crs1.falseEasting==crs2.falseEasting) # The false easting of a projected coordinate system.1 
 assert(crs1.falseNorthing==crs2.falseNorthing) # The false northing of a projected coordinate system.1 
 assert(crs1.MFalseOriginAndUnits==crs2.MFalseOriginAndUnits) # The measure false origin and units.
 assert(crs1.MResolution==crs2.MResolution) # The measure resolution.
 assert(crs1.MTolerance==crs2.MTolerance) # The measure tolerance.
 assert(crs1.XYTolerance==crs2.XYTolerance) # The xy tolerance.
 assert(crs1.ZDomain==crs2.ZDomain) # The extent of the z domain.
 assert(crs1.ZFalseOriginAndUnits==crs2.ZFalseOriginAndUnits) # The z false origin and units.
 assert(crs1.factoryCode==crs2.factoryCode) # The factory code or well-known ID (WKID) of the spatial reference.
 assert(crs1.isHighPrecision==crs2.isHighPrecision) # Indicates whether the spatial reference has high precision set.
 assert(crs1.latitudeOf1st==crs2.latitudeOf1st) # The latitude of the first point of a projected coordinate system.1
 assert(crs1.latitudeOf2nd==crs2.latitudeOf2nd) # The latitude of the second point of a projected coordinate system.1 
 assert(crs1.latitudeOfOrigin==crs2.latitudeOfOrigin) # The latitude of origin of a projected coordinate system.1 
 assert(crs1.linearUnitCode==crs2.linearUnitCode) # The linear unit code. 
 assert(crs1.linearUnitName==crs2.linearUnitName) # The linear unit name.1
 assert(crs1.longitude==crs2.longitude) # The longitude value of this prime meridian.1
 assert(crs1.longitudeOf1st==crs2.longitudeOf1st) #The longitude of the first point of a projected coordinate system.1
 assert(crs1.longitudeOf2nd==crs2.longitudeOf2nd) # The longitude of the second point of a projected coordinate system.1
 assert(crs1.longitudeOfOrigin==crs2.longitudeOfOrigin) # The longitude of origin of a projected coordinate system.1
 assert(crs1.metersPerUnit==crs2.metersPerUnit) # The meters per linear unit.1
 assert(crs1.projectionCode==crs2.projectionCode) # The projection code.1
 assert(crs1.projectionName==crs2.projectionName) # The projection name.1
 assert(crs1.scaleFactor==crs2.scaleFactor) # The scale factor of a projected coordinate system.1
 assert(crs1.standardParallel1==crs2.standardParallel1) # The first parallel of a projected coordinate system.1
 assert(crs1.standardParallel2==crs2.standardParallel2) # The second parallel of a projected coordinate system.1
 assert(crs1.angularUnitCode==crs2.angularUnitCode) # The angular unit code.2
 assert(crs1.angularUnitName==crs2.angularUnitName) # The angular unit name.2
 assert(crs1.datumCode==crs2.datumCode) # The datum code.2
 assert(crs1.datumName==crs2.datumName) # The datum name.2
 assert(crs1.flattening==crs2.flattening) # The flattening ratio of this spheroid.2
 assert(crs1.longitude==crs2.longitude) # The longitude value of this prime meridian.2
 assert(crs1.primeMeridianCode==crs2.primeMeridianCode) # The prime meridian code.2
 ## Prob can be ignored
 if strict:
 assert(crs1.ZResolution==crs2.ZResolution) # The z resolution property.
 assert(crs1.ZTolerance==crs2.ZTolerance) # The z-tolerance property.
 assert(crs1.hasMPrecision==crs2.hasMPrecision) # Indicates whether m-value precision information has been defined.
 assert(crs1.hasXYPrecision==crs2.hasXYPrecision) # Indicates whether xy precision information has been defined.
 assert(crs1.hasZPrecision==crs2.hasZPrecision) # Indicates whether z-value precision information has been defined.
 assert(crs1.XYResolution==crs2.XYResolution) # The xy resolution.
 assert(crs1.domain==crs2.domain) # The extent of the xy domain.
 assert(crs1.MDomain==crs2.MDomain) # The extent of the measure domain.
 assert(crs1.remarks==crs2.remarks) # The comment string of the spatial reference.
 assert(crs1.type==crs2.type) # The type of the spatial reference. Geographic: A geographic coordinate system. Projected: A projected coordinate system.
 assert(crs1.usage==crs2.usage) # The usage notes. 
 assert(crs1.classification==crs2.classification) # The classification of a map projection.1 
 assert(crs1.GCSCode==crs2.GCSCode) # The geographic coordinate system code.2
 assert(crs1.GCSName==crs2.GCSName) # The geographic coordinate system name.2
 assert(crs1.primeMeridianName==crs2.primeMeridianName) # The prime meridian name.2
 assert(crs1.radiansPerUnit==crs2.radiansPerUnit) # The radians per angular unit.2
 assert(crs1.semiMajorAxis==crs2.semiMajorAxis) # The semi-major axis length of this spheroid.2
 assert(crs1.semiMinorAxis==crs2.semiMinorAxis) # The semi-minor axis length of this spheroid.2
 assert(crs1.spheroidCode==crs2.spheroidCode) # The spheroid code.2
 assert(crs1.spheroidName==crs2.spheroidName) # The spheroid name.2
 return(True)
 except:
 output_message="CRS differs between datasets."#\ncrs1: %s\ncrs2 : %s" %(crs1.exportToString(), crs2.exportToString())
 print(output_message)
 return(False)
 ## Differs to the falseEasting and falseNorthingUnits are odd on occasion but false eastings and northings make sense
 # crs.falseOriginAndUnits # The false origin and units.
 ## Not required
 #crs.GCS # A projected coordinate system returns a SpatialReference object for the geographic coordinate system it is based on. A geographic crs.coordinate system returns the same SpatialReference.
 #crs.SpatialReference
 #crs.VCS # If the coordinate system has a vertical coordinate system, it returns a VCS object for the vertical coordinate system it is based on.
 #crs.abbreviation # The abbreviated name of the spatial reference.
 #crs.alias # The alias of the spatial reference.

Given the above, you might use them like:

dataset1="your_vector_1.shp"
dataset2="your_vector_2.shp"
assert_crs_attribs(dataset1, dataset2)

Given your use case, hopefully the asserts won't fail.

I integrate these functions now into many processes such as where I have a range of spatial datasets that I'm joining and want to eliminate any doubt that things were misaligned.