ArcGIS Field Calculator – How to Get JSON Text

arcgis-10.7arcmaparcpyfield-calculatorjson

In ArcMap 10.7.1 (with an Oracle 18c SDE.ST_GEOMETRY polyline FC):

I want to use the Field Calculator (Python) in the Attribute Table to get a feature's JSON text.

Pre-Logic Script Code:
----------------------
def wJson(shp):
 pnts = shp.JSON
 return str(pnts)

Expression: JSON = 
----------------------    
wJson( !SHAPE! )

When I run that field calculation, I don't get an error, but it doesn't populate a value in the field (remains null).

What am I doing wrong? How can I get that field calculation to return a value?

Best Answer

Try the actual Field Calculator tool and run the workflow as it'll log warnings (which you don't see when doing from the right click menu). When I run that, I get a warning that one of the values cannot be written to the field and returns null

It fails because my field is the default size of 255 characters, but the output JSON for me is over 600 characters. Thus, my fix, would be to either truncate the JSON going into the field or create a new, larger text field.

Related Solutions

[GIS] Create list of [X, Y] coordinates within field calculator

I am going to provide an alternative using the python interactive console in ArcMap.

I find it is easier to deal with python code like this using the interactive console. I am sure if you are very stuck with using the Field Calculator, this can be adapted to it.

rows = arcpy.da.UpdateCursor(yourLayer, ["SHAPE@", "fieldToStoreInfo"]) 
for row in rows:
     coords = []
     for i in range(row[0].partCount):
         parts = row[0].getPart(i)
         for part in parts:
             coords.append((part.X, part.Y))
     row[1] = str(coords)
     rows.updateRow(row)

SHAPE@ returns a geometry object which lets you check its part count (vertices). Then you can iterate through all the parts to get each one's X and Y values. Append it to your list and when you return you convert the list to a string. The value that gets stored is like:

[(2924327.0050581694, 10204574.257406339), (2924318.8784340024, 10204555.405738011), (2924317.0618365854, 10204533.60164775), (2924322.5132692605, 10204520.88152884), (2924331.5985529274, 10204511.796245173), (2924366.122762084, 10204511.796245173)]

Also, make sure your field has enough space for a long list of coordinate points. I set mine at a crazy high number just because my test file was a set of utility lines.

[GIS] Calculating row in field based off another row in same field using ArcGIS Field Calculator

Something like this should work - Finds all the values in Field1 and Field2 and stores them in a dictionary, then looks up that dictionary for the values to calculate the field.

You will need to update "Field1" and "Field2" in the cursor with your actual field names, and "MyFC" with the name of your layer.

Pre-Logic Script:

myDict = {}
with arcpy.da.SearchCursor("MyFC", ["Field1", "Field2"]) as cursor:
  for row in cursor:
    if row[1] and row[0] not in myDict:
      myDict[row[0]] = row[1]

def Calc( field1 , field2 ):
  global myDict
  if not field2:
    x = myDict[field1]
  else:
    x = field2
  return x

Field2=

Calc( !Field1! , !Field2! )

Best Answer

Related Solutions

[GIS] Create list of [X, Y] coordinates within field calculator

[GIS] Calculating row in field based off another row in same field using ArcGIS Field Calculator

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