topic Re: Calculate field @SQUAREMETERS in Python Questions

Calculate field @SQUAREMETERS

RyanStephany — Fri, 08 Jul 2011 14:37:22 GMT

Could anyone tell me why calculating the shape.length@METERS works for me, but calculating shape.area@SQUAREMETERS does not. Area always returns '0'. I'm using 9.3, and the feature classes are in WGS 84.

Here are 2 examples:

~Length
gp.CalculateField_management(fc , field.name, '!SHAPE.LENGTH@METERS!', "PYTHON_9.3"

~Area
gp.CalculateField_management(fc , field.name, '!SHAPE.AREA@SQUAREMETERS!', "PYTHON_9.3"

Re: Calculate field @SQUAREMETERS

DarrenWiens2 — Fri, 08 Jul 2011 15:51:03 GMT

SQUAREMETERS works for me the way you have it - but I'm using ArcGIS 10. Sorry to ask this, but you're not trying to calculate the area for a line feature class, are you?

Re: Calculate field @SQUAREMETERS

RyanStephany — Fri, 08 Jul 2011 18:46:37 GMT

don't be sorry, no I'm not calculating the area of a line, I did find something though.
It was returning '0' because I was only trying to keep 2 decimal places. I am getting values, but they do not seem to be in meters squared. When you tried it in 10 was the output of the calculation correct?

this is part of the actual code

my_fields = {'Polyline':{'LEN': '!SHAPE.LENGTH@METERS!'}, 'Polygon' : {'ARA': '!SHAPE.AREA@SQUAREMETERS!'}}

gp.CalculateField_management(fc , field.name, '"%.2f" % float('+ self.my_fields[desc.ShapeType][field.name]+ ')', "PYTHON_9.3")

Re: Calculate field @SQUAREMETERS

RyanStephany — Fri, 08 Jul 2011 18:52:59 GMT

so the field I'm trying to calculate is populated with the same as the Shape_AREA field.
Shape_AREA = 0.000651
my_calculated_field = 0.000651
What_i_want = 6974972.61

Re: Calculate field @SQUAREMETERS

DanPatterson_Retired — Fri, 08 Jul 2011 18:54:55 GMT

Did you try projecting the file first?

Re: Calculate field @SQUAREMETERS

RyanStephany — Fri, 08 Jul 2011 19:06:30 GMT

i tried reprojecting in the cursor, but got the same results.

Re: Calculate field @SQUAREMETERS

RyanStephany — Fri, 08 Jul 2011 19:09:31 GMT

What I don't understand is that converting !Shape.Length@METERS! works for polylines, but !Shape.Area@SQUAREMETERS! for polygons does not do any conversion.