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Calculate Geometry in Model Builder

CaseyBentz

I am looking for an easy method, similar to how you do it in ArcMap, to calculate geometry for two fields. I want to add the lat and long to a point feature class that I have. The coordinate system of the point feature class is not in geographic coordinates. Any ideas.

Casey

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RichardFairhurst

Does anyone know if line mid-points (not centroid) can be programmatically calculated outside of the Calculate Geometry tool in the attribute table? I need mid XY values calculated as part of a model builder process.

Any ideas would be great....thanks!

I believe you could use the geometry of the line from the shape field with the positionAlongLine (value, {use_percentage}) operation at the .5 position with the percentage option set as True. This would return a point from which you could get X and Y coordinates.

TonySalomone

Does anyone know if line mid-points (not centroid) can be programmatically calculated outside of the Calculate Geometry tool in the attribute table? I need mid XY values calculated as part of a model builder process.

Any ideas would be great....thanks!

CarolKraemer1

It could have to do with any number of factors. ArcObjects (Geometry Calculator) and Python (Field Calculator) may handle geometry differently, although I would consider that a better candidate if this was a geodatabase with true curves rather than a shapefile with densified curves. The Spatial Reference may be accessed differently by the two methods. Are you sure your data frame is using the coordinate system of the polygons you are calculating for the Geometry Calculator? You could also try specifying the coordinate system explicitly in the environment setting of the Field Calculator tool to see if that made any difference.

It is a black box, so no one but the programmers involved could say for sure how the calculation processes differ and what factors could produce the results you are seeing. Most likely both results are correct according to the method applied. Insufficient information exists to determine which method you would prefer to apply or how to remove the discrepancy in the methods.

Thank you for your reply, Richard. Yes, I'm certain about the Spatial References both for the files and the dataframe I'm using. It must be the dreaded black box. I've run across this issue before using things like Raster Calculator and ArcSWAT tools (don't judge, it was during my senior year in college 🙂 ).

The differences won't have an impact on my current task at hand but it would be nice to know in case it would in the future, for me or anyone else.

Happy GISing!

RichardFairhurst

On the same field (Double) of a shapefile, I used both the Calculate Geometry (in attribute table) and Calculate Field (in Model Builder) using the !shape.area@acres! to calculate Acres. The goal is to have Acres calculated within a model. My question is, why would I get slightly different results when using the two methods?

Using Field Calculator (in attribute table) and Calculate Field (in Model Builder):
[ATTACH=CONFIG]32745[/ATTACH]

Using Calculate Geometry (in attribute table):
[ATTACH=CONFIG]32746[/ATTACH]

I know the difference is small but it's still a difference that makes me wonder which is correct.

I'm using ArcMap version 10.2.0.3348 64-bit on Windows 8, in case that helps.

Thank you in advance for any knowledge you share!
-Carol

It could have to do with any number of factors. ArcObjects (Geometry Calculator) and Python (Field Calculator) may handle geometry differently, although I would consider that a better candidate if this was a geodatabase with true curves rather than a shapefile with densified curves. The Spatial Reference may be accessed differently by the two methods. Are you sure your data frame is using the coordinate system of the polygons you are calculating for the Geometry Calculator? You could also try specifying the coordinate system explicitly in the environment setting of the Field Calculator tool to see if that made any difference.

It is a black box, so no one but the programmers involved could say for sure how the calculation processes differ and what factors could produce the results you are seeing. Most likely both results are correct according to the method applied. Insufficient information exists to determine which method you would prefer to apply or how to remove the discrepancy in the methods.

CarolKraemer1

On the same field (Double) of a shapefile, I used both the Calculate Geometry (in attribute table) and Calculate Field (in Model Builder) using the !shape.area@acres! to calculate Acres. The goal is to have Acres calculated within a model. My question is, why would I get slightly different results when using the two methods?

Using Field Calculator (in attribute table) and Calculate Field (in Model Builder):
[ATTACH=CONFIG]32745[/ATTACH]

Using Calculate Geometry (in attribute table):
[ATTACH=CONFIG]32746[/ATTACH]

I know the difference is small but it's still a difference that makes me wonder which is correct.

I'm using ArcMap version 10.2.0.3348 64-bit on Windows 8, in case that helps.

Thank you in advance for any knowledge you share!
-Carol

fieldcalculator.png

calculategeometry.png

LewSovocool

I think 3D length is not supported using the field calculator (at least not this syntax). The only listed defined keywords for the shape components are: type, extent, centroid, firstPoint, lastPoint, area, length, isMultipart, and partCount.

I believe you are limited to using the LENGTH_3D option of the Add Z Information tool. Then you would have to apply a unit conversion from your base units to miles.

No guarantee this will work, but since the 3D Analyst tool uses the term LENGTH_3D as the keyword and I don't see that variant listed above, you could try: !shape.length_3D@miles!

Thanks Richard, but I think you were correct that 3D length is not supported using the field calculator tool in this context. I tried !shape.length_3D@miles! and received the same error. Thanks for your help though!

RichardFairhurst

I'm trying to use the Calculate Field tool to calculate the 3D Length of an interpolated line and I can't seem to figure out the correct syntax for the expression. I've tried !shape.3Dlength@miles!, !shape.length3D@miles!, !shape.3D_length@miles!, and !shape.3D length@miles! but I keep getting an error. Any thoughts?

I think 3D length is not supported using the field calculator (at least not this syntax). The only listed defined keywords for the shape components are: type, extent, centroid, firstPoint, lastPoint, area, length, isMultipart, and partCount.

I believe you are limited to using the LENGTH_3D option of the Add Z Information tool. Then you would have to apply a unit conversion from your base units to miles.

No guarantee this will work, but since the 3D Analyst tool uses the term LENGTH_3D as the keyword and I don't see that variant listed above, you could try: !shape.length_3D@miles!

LewSovocool

!SHAPE.AREA@SQUAREMILES!

Here is the help topic I am consulting on the topic: Using the Calculate Field tool

I'm trying to use the Calculate Field tool to calculate the 3D Length of an interpolated line and I can't seem to figure out the correct syntax for the expression. I've tried !shape.3Dlength@miles!, !shape.length3D@miles!, !shape.3D_length@miles!, and !shape.3D length@miles! but I keep getting an error. Any thoughts?

DavidTreering

In the Calculate Field tool, use the following python expression.
def find(shape):
  point = shape.getPart(0)
  return point.X
find(!Shape!)
(sub point.Y to get the Y coordinates)

This works beautifully. Thank you!

RichardFairhurst

Richard:
Do you know the syntax to calculate area in Square Miles? Thanks in advance for your time...
Mark

!SHAPE.AREA@SQUAREMILES!

Here is the help topic I am consulting on the topic: Using the Calculate Field tool

MarkEnglish

Richard:
Do you know the syntax to calculate area in Square Miles? Thanks in advance for your time...
Mark

MarkEnglish

Perfect, I originally didn't add the @mile. Thanks Richard for your time!

RichardFairhurst

I ran a test run, and although the fields are populated, their units aren't in miles. I must be missing something simple... I am using Arc10, and I have converted to an appropriate equal distance projection. Regards...

I am not sure how much influence the dataframe has on the field calculator. I suspect it only uses the native projection and units of the feature class when you just put !Shape.Length!.

If you are OK with the original projection of the feature class, at 10 I believe if you choose the Python 9.3 option in the Model Builder Field Calculator tool you can adjust units by using:

!Shape.Length@Miles! # or substitute any other appropriate units for Length.

I am not sure how to emulate the geometry calculator's ability to apply the dataframe projection to feature classes that were stored using a different projection through the field calculator (At least not in Python. At 9.3 VBA would do it, but not at 10 using VB script).

MarkEnglish

I ran a test run, and although the fields are populated, their units aren't in miles. I must be missing something simple... I am using Arc10, and I have converted to an appropriate equal distance projection. Regards...

MarkEnglish

So, using the calculate field function in Model Builder. I just need to my emplty field to equal !Shape.Length!? How does it know the calculation is set to miles? Thanks for your time!

GeorgeNewbury

If you are looking to calculate the geometry of a shape and then put that value in a field, then you can do with python. Look at the ArcGIS Desktop Help under 'Calculate Field Examples', towards to the bottom it shows how to calculate geometry. For example

Area: !Shape.Area!
Length: !Shape.Length!
X/Y/Z/M for first point in a line !Shape.firstPoint.X!

If you are looking to convert units (e.g. KM to Miles) you can even do that within the expression.

So drag in the 'Calculate Field' tool to Modelbuilder, and then build the expression to calculate the geometry you need. (Note I'm assuming your using 10.0+, I don't think this Python capability was in pre 10)

MarkEnglish

Hello:
I saw this post, and since it related to my quesiton, I decided to add here. I am basically trying to calculate geometry for two fields using model builder. The first field is predefined as 'Total Miles' to house total mileage for all stream segments in that field. The second is 'Need miles' that will house mileage for a fraction of the records. I'll determine what records using select by attributes, then calculate geometry (mileage). My final predefined field is the percentage of Need Miles to the Total Miles, which I can derive using Calculate field in model builder. I know, too much information. Basically, I just need to know how to Calculate Geometry in model builder? I can't seem to locate the function in stand-alone format to drag in to model builder, and assume there is another approach, most likely a simple one. Thanks in advance!
Mark

StephanieWendel

Great! Glad to hear that worked good for you! :cool:

CaseyBentz

Thank you Stephanie, I used the add field and calculate field option.

Casey

StephanieWendel

You can use the Add XY Coordinates tool to expose the xy coordinates of your point data. See this link http://http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//001700000032000000.htm

You should be able to use this in a model. However, before you do this you would need to re-project the data into a geographic coordinate system like WGS1984 or NAD1983 to get the values in decimal degrees. You would run the tool on this new feature class and that is where the information would be put. You can then do a join on data that is in the projected coordinate system to get its long/lats in decimal degrees.

Also in the model, you can also use Add Field then the Calculate Field tools. In the Calculate Field tool, use the following python expression.

def find(shape):
  point = shape.getPart(0)
  return point.X

find(!Shape!)

(sub point.Y to get the Y coordinates)

This will however use the coordinate system of the data so again you may need to re-project the data before you use the Calculate Field tool. Again, you can join the data back to your projected coordinate dataset.

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