ArcMap 10.7.1 — Oracle 18c SDE.ST_GEOMETRY

I have a polyline FC that has true curves.

And I have an ArcPy script that updates the M-values of the vertices in the lines:

import arcpy
connection = "Database Connections\my_conn.sde"
feature_class = connection + "\my_owner.my_fc"
spatial_reference = arcpy.Describe(feature_class).spatialReference

with arcpy.da.Editor(connection) as edit_session:
    with arcpy.da.UpdateCursor(feature_class, "SHAPE@") as cursor:
        for row in cursor:
            geometry = row[0].densify("ANGLE", 10000, 0.174533)
            parts = arcpy.Array()
            for part in geometry:
                points = arcpy.Array()
                for point in part:
                    point.M = geometry.measureOnLine(point)
            row[0] = arcpy.Polyline(parts, spatial_reference)

The script reconstructs and replaces the geometry of the lines. So, unfortunately, it removes the true curves from the shapes.

Before running script:

enter image description here

After running script:

enter image description here


With ArcPy, is there a way to edit vertices without removing true curves from the SHAPE?

For example, is there way to do something like this?

UpdateVertex (shape, partNum, vertexNum, [x, y, z, m]) 


True Curves = True Evil

Idea: ArcPy - Edit vertex without removing true curves

  • 1
    You've got a huge corruption-ready bug in this script. All arcpy.Geometry constructors should always be provided with a SpatialReference parameter. Failure to do so means the default resolution will be applied at construction, then the actual SpatialReference silently applied on insert, resulting in truncation of coordinate values to 3 or 4 decimal places and possible geometry corruption (depending on magnitude). The Geometry itself has a hasCurves property which will let you know if you are about to corrupt the shape, but only ArcObjects can capture and re-apply the CAD (maybe).
    – Vince
    Commented Feb 3, 2022 at 22:17
  • @Vince Thanks. Regarding the hasCurves property: it looks like that property isn't available in ArcGIS Desktop 10.7.1. desktop.arcgis.com/en/arcmap/10.7/analyze/arcpy-classes/…
    – User1974
    Commented Feb 4, 2022 at 18:23
  • All the more reason to migrate to Pro, I guess.
    – Vince
    Commented Feb 4, 2022 at 21:41
  • @Vince : Regarding "You've got a huge corruption-ready bug in this script." I've updated the script in this post. How does it look now? (For what it's worth, I also posted it on the Code Review Stack Exchange site: Loop through polyline vertices and update coordinate.)
    – User1974
    Commented Feb 5, 2022 at 6:32
  • with obviates need for the del lines, and string math is inefficient/clumsy compared to using os.path.join().
    – Vince
    Commented Feb 5, 2022 at 11:46

1 Answer 1


I guess you can manipulate it using JSON.

For example, this field calculator expression, when I run it on a buffer of a point:

import json
def wJson(shp):
 pnts = json.loads(shp.JSON)
 #esriJSON = arcpy.AsShape(pnts, True)
 return str(pnts)
wJson( !Shape!)


{u'curveRings': [[[1727075.9359999998, 5946765.4923], {u'a': [[1727075.9359999998, 5946765.4923], [1717013.4664801424, 5946765.4923], 0, 1]}]], u'spatialReference': {u'wkid': 2193, u'latestWkid': 2193}}

Which is just a dictionary. You can use:

esriJSON = arcpy.AsShape(pnts, True)

after amending the dictionary.

Also see getPart() method returns incorrect geometry from buffer in ArcGIS


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