Bearing Distance to Line Output Bearings <> Input Numbers

[RandyMcGregor3]

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

[DanPatterson]

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)

[RandyMcGregor3]

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)?

[DanLee · Accepted solution]

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]

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,

[DanLee]

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.

[Klaus_B_Vestergaard]

Hi @DanLee 

Good to see that "Planar Line" is now an option in 3.0.2 (I've never got to use it in 2.9) ;o)

However, it's a bit confusing, that in order to pick "Planar Line", first you have to pick a projected coordinate system.

Intuitively, I'd look for "Planar Line" first in the drop-down as Line Type comes first in the GUI, before Spatial Reference.

As the default Spatial Reference is GCS_WGS84, you don't get to pick "Planar" from Line Type.

Picking a projected CRS in Spatial Reference first, then scroll down to pick Line Type would appear more logic - to me at least?

Regards, Klaus

[DanLee]

I agree with you from logical point of view, especially now the Planar Line option and PCS (projected coordinate system) are supported. However the parameter ordering on the tool dialog has been there for many years; most of users who want various geodetic lines may not need to worry about the default SR. Switching the parameter ordering now may confuse existing users; and more impactfully it may require updates to existing user documentation or guidelines. I am certainly concerned about that.  🙂

Having parameter ordering on the tool dialog different from python syntax which absolutely cannot be changed may also cause confusion and mistakes. We usually would avoid that unless the change is widely request and justified.  Such change does happen but very seldomly.