Bearing Distance to Line Output Bearings <> Input Numbers

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05-06-2021 01:23 PM
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RandyMcGregor3
Occasional Contributor II

The table below contains the numbers used for direction (decimal degrees) with the Bearing Distance to Lines tool (Azimuth_Ed field) and the result of Calculate Geometry Attributes tool (AZ_Test field).

The tool was run on x,y numbers with state plane, Illinois East coordinate system with that coordinate system set as the output coordinate system.

They don't match. Is this a result of the complex math used to calculate the lines and is expected, or should I be concerned?

Thank  you,

Randy McGregor

RandyMcGregor3_0-1620332208266.png

 

 

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DanLee
by Esri Regular Contributor
Esri Regular Contributor

The Line Bearing from Calculate Geometry Attributes tool or Add Geometry Attributes is planar, whilst the Azimuth_Ed used in Bearing Distance To Line is geodetic. The differences between them are expected.

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DanPatterson
MVP Esteemed Contributor

Bearing Distance To Line (Data Management)—ArcGIS Pro | Documentation

which option did you use?  geodesic, rhome-line, great circle, normal section?  geodesic is the default, but just checking.

Your distances are fairly long... Is suspect that they will be much closer for shorter distances.

You can check some of the math involved here

Calculate distance and bearing between two Latitude/Longitude points using haversine formula in Java...

 

PS also note that you planar distances aren't exactly the same either (small but there)

 

 


... sort of retired...
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RandyMcGregor3
Occasional Contributor II

Thanks for the feedback. I am not able to follow that math, though. I am using the geodesic default. The numbers I get are very different based on coordinate system, so I think this is a difference resulting from geographic complexity.

I made a line with the direction/distance option, selecting 45 degrees and it ended up very very close to to the line I had created with the Bearing Distance to Lines tool and then ran Calculate Geometry with Line Bearing and got a value of 53.1 degrees. So, it looks like the Line Bearing calculation is incorporating geographic complexities. 

I need to break up areas by degrees (0,45,90 etc..) and am checking to make sure the results are valid and can be used for geoprocessing - Is this feature in the sector between 45 and 90 degrees (NE to E)?

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DanLee
by Esri Regular Contributor
Esri Regular Contributor

The Line Bearing from Calculate Geometry Attributes tool or Add Geometry Attributes is planar, whilst the Azimuth_Ed used in Bearing Distance To Line is geodetic. The differences between them are expected.

Klaus_B_Vestergaard
New Contributor

Hi DanLee

Just for my understanding...

the Line Bearing from Calculate Geometry Attributes tool or Add Geometry Attributes is relative to Grid North (planar) if working in a projected coordinate system - true?

If so the Bearing used in Bearing Distance To Line is relative to True North (geodetic) - correct?

Thanks,

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DanLee
by Esri Regular Contributor
Esri Regular Contributor

Yes, that's correct. 

By the way we have added a "planar line" option for output in a projected coordinate system in ArcGIS Pro 2.9.

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