Seeing that my issue on GitHub (areas_and_lengths Incorrect Default area_unit · Issue #106 · Esri/arcgis-python-api · GitHub) hasn't even been acknowledged in 6+ months, I am hoping that posting it here might get better traction since there are still issues with areas_and_lengths.
As an aside, I can't help but shake my head when reading Open Source | Esri's Open Vision:
Esri’s Open-Source Community on GitHubAt Esri we encourage our development staff to engage with the open-source community. We regularly work on and share open-source projects via GitHub. We welcome more interactions with the community of geospatial developers on this forum. |
I might be able to give them "sharing" but "regularly working" seems a stretch when issues can go unacknowledged, not even addressed, in 6+ months.
The areas_and_lengths - arcgis.geometry module — arcgis 1.3.0 documentation states (red color added by me):
length_unit - The length unit in which the perimeters of polygons will be calculated.
If calculation_type is planar, then length_unit can be any esriUnits constant. If lengthUnit is not specified, the units are derived from spatial_ref. If calculationType is not planar, then lengthUnit must be a linear esriUnits constant, such as esriSRUnit_Meter or esriSRUnit_SurveyMile. If length_unit is not specified, the units are meters. For a list of valid units, see esriSRUnitType Constants and esriSRUnit2Type Constant.
area_unit - The area unit in which areas of polygons will be calculated.
If calculation_type is planar, then area_unit can be any esriUnits constant. If area_unit is not specified, the units are derived from spatial_ref. If calculation_type is not planar, then area_unit must be a linear esriUnits constant such as esriSRUnit_Meter or esriSRUnit_SurveyMile. If area_unit is not specified, then the units are meters. For a list of valid units, see esriSRUnitType Constants and esriSRUnit2Type constant. The list of valid esriAreaUnits constants include, esriSquareInches | esriSquareFeet | esriSquareYards | esriAcres | esriSquareMiles | esriSquareMillimeters | esriSquareCentimeters | esriSquareDecimeters | esriSquareMeters | esriAres | esriHectares | esriSquareKilometers.
I can't speak for others, but "if area_unit is not specified" sure makes me think it is an optional argument, right? The problem is, the error message returned by ArcGIS API for Python says there are required:
>>> from arcgis import gis, geometry
>>>
>>> gis = gis.GIS()
>>>
>>> geom_json = {
... "rings": [[[0, 0], [0, 10], [10, 10],[10, 0],[0, 0]]],
... "SpatialReference": {"wkid": 3857}
... }
>>>
>>> geom = geometry.Geometry(geom_json)
>>> geometry.areas_and_lengths(geom, spatial_ref=3857)
TypeError Traceback (most recent call last)
<ipython-input-12-3059784b616c> in <module>()
----> 1 geometry.areas_and_lengths(geom, spatial_ref=3857)
TypeError: areas_and_lengths() missing 3 required positional arguments: 'length_unit', 'area_unit', and 'calculation_type'
OK, so they are required by Python but don't need to be specified by ArcGIS. Let's try the old Esri standby of passing empty strings to use defaults:
>>> geometry.areas_and_lengths(geom, "", "", "", 3857)
RuntimeError: Error computing areas and lengths
(Error Code: 500)
Well, it seems empty strings don't work either. To confuse the matter even more, specifying only the area units works while leaving the other two empty strings:
>>> geometry.areas_and_lengths(geom,"", "esriSquareMeters", "", 3857)
{'areas': [100], 'lengths': [40]}
At this point, I am totally confused how exactly I am supposed to call areas_and_lengths because the documentation doesn't describe reality, and the method itself doesn't even behave consistently with unspecified parameters.
