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Calculate Geometry Coordinate System

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09-15-2023 07:50 AM
Craig_Eissler_Iceman
Occasional Contributor III

The Calculate Geometry (Calculate Geometry Attributes) tool has an input for Coordinate System.

Is there a reason anyone would choose something other than the coordinate system than what the input layer is set to?

...Seems to me this could really make things confusing.

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DanPatterson
MVP Esteemed Contributor

If the coordinate system is geographic, then you would specify a projected coordinate system to get planar geometry measures.

If your coordinate is already projected, such as in a UTM projection, then specifying a State Plane/Modified Transverse mercator, you would get slightly different planar measures since scale factors of the central meridians differ (utm - 0.9996, mtm = 0.9999 )

If your data were sadly in a web mercator projected coordinate , then the planar measures would be really bad and you should be inclined to pick a better conformal, equal area or equidistant one to get more appropriate values.


... sort of retired...

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clt_cabq
Occasional Contributor III

I've seen a lot of situations where standards require a dataset to be projected in a particular coordinate system, but reporting needs want coordinates presented in some flavor of lat/lon. You are correct though, it can be confusing, and it is one reason I almost never trust coordinate values that are in attributes of a feature class without validating they are correct. 

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5 Replies
DanPatterson
MVP Esteemed Contributor

If the coordinate system is geographic, then you would specify a projected coordinate system to get planar geometry measures.

If your coordinate is already projected, such as in a UTM projection, then specifying a State Plane/Modified Transverse mercator, you would get slightly different planar measures since scale factors of the central meridians differ (utm - 0.9996, mtm = 0.9999 )

If your data were sadly in a web mercator projected coordinate , then the planar measures would be really bad and you should be inclined to pick a better conformal, equal area or equidistant one to get more appropriate values.


... sort of retired...
Craig_Eissler_Iceman
Occasional Contributor III

Right, I know, ...but is this a good idea?

Seems to me, this could be rather confusing, and that it would be better to just (re)project the data into different coordinate systems rather than mixing those respective values in the same layer/table.

I understand the reasons for having different "units" in the same layer/table, but mixing coordinate system calculations seems risky to me

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clt_cabq
Occasional Contributor III

I've seen a lot of situations where standards require a dataset to be projected in a particular coordinate system, but reporting needs want coordinates presented in some flavor of lat/lon. You are correct though, it can be confusing, and it is one reason I almost never trust coordinate values that are in attributes of a feature class without validating they are correct. 

Craig_Eissler_Iceman
Occasional Contributor III

OK thanks. ...Yeah, I think for me, I'll just re-project it if that's what I'm looking for 😁

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jerrysmith43345
New Contributor

Calculating coordinates in a geometry coordinate system involves determining the position of a point or object within that system. The most common coordinate system is the Cartesian coordinate system, which uses two or three numerical values through BMI Calculator (coordinates) to represent the location of a point in space.