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Unsure of the "distance" result from NeigbourFinder

  • October 31, 2024
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thomastupuivao
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I have a pair of longitude latitude coordinates that I’m trying to measure the distance between in KM

If I cross-reference this “distance” result in ArcGIS Pro, I get approximately 1.44km

This is also roughly the same result if I use a online calculator;

My question, is how does the result 0.01630799258600798 translate to 1.44km? is there something I’m missing??

Best answer by redgeographics

What @virtualcitymatt said, it’s the distance in degrees, the corresponding length in meters depends on your position on earth as well as the direction in which you’re measuring. 

Consulting my cheatsheet:

0.01 degree of latitude is 1.113 km
at a latitude of -45 degrees 0.01 degree of longitude is 0.788 km

So… ballpark off the top of my head math, looking at the direction of your line, I’d say it’s correct.

You can try the GeographicLengthCalculator (as described here) as an alternative to Matt’s suggestion.

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virtualcitymatt
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  • November 1, 2024

While I’m not 100% sure on this - typically most transformers perform calculations based on the x-y units. In this case the “distance” is likely a result if FME assumed that the coordinates were all in meters (or feet) rather than Lat-Long (i.e the result is in decimal degrees). Essentially I don’t think FME takes in to account the coordinate systems here when performing these kinds of calculations.

Typically it is recommended to first project the data into an appropriate local (grid based) coordinate system. Then you will get meters (or feet) as a result. 

Here’s some more reading which might help:

https://support.safe.com/hc/en-us/articles/25407476391821-Coordinate-Systems-and-Measurements-with-the-Reprojector
 


redgeographics
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  • November 1, 2024

What @virtualcitymatt said, it’s the distance in degrees, the corresponding length in meters depends on your position on earth as well as the direction in which you’re measuring. 

Consulting my cheatsheet:

0.01 degree of latitude is 1.113 km
at a latitude of -45 degrees 0.01 degree of longitude is 0.788 km

So… ballpark off the top of my head math, looking at the direction of your line, I’d say it’s correct.

You can try the GeographicLengthCalculator (as described here) as an alternative to Matt’s suggestion.


thomastupuivao
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  • November 2, 2024

Awesome thank you for that.