BearingDistanceToLine not supporting spatial_reference

05-14-2012 11:47 AM
Occasional Contributor III
I have been getting disappointing results from BearingDistanceToLine_management in v10.0 when using a Polar Stereographic projection.

In, for example, the upper right quadrant (where the pole is to the lower left), feeding the tool a direction of, say 14° (measured clockwise from the y axis), plots the line traveling from the start point in a direction 14° clockwise from the direction of the pole (at 0,0)!

This behavior is rather less than useful.

I have tried feeding the spatial reference as a spatial reference string in a python script, and by Importing it from another feature class in the tool interface, with the same result either way.

The projection is:

Projection: Stereographic_North_Pole
False_Easting: 0.000000
False_Northing: 0.000000
Central_Meridian: 180.000000
Standard_Parallel_1: 60.000000
Linear Unit: Meter (1.000000)

Geographic Coordinate System: GCS_WGS_1984
Angular Unit: Degree (0.017453292519943299)
Prime Meridian: Greenwich (0.000000000000000000)
Datum: D_WGS_1984
   Spheroid: WGS_1984
     Semimajor Axis: 6378137.000000000000000000
     Semiminor Axis: 6356752.314245179300000000
     Inverse Flattening: 298.257223563000030000

or, if you prefer:
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3 Replies
by Esri Regular Contributor
Esri Regular Contributor

Thanks for posting the issue. We are investigating.

Did you enter the starting point location as long and lat or as x and y in the intended projection?
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Occasional Contributor III
As x and y in the named Stereographic.

As I was doing it then (I have since developed a work around that does not use the BearingDistanceToLine tool), I had two sets of points: one that represented the start point and the other that was a dummy end point. (so I could get the angle I wanted even if the length was wrong)
These were originally plotted in lat / long, and then projected to the stereographic space.
I used AddXY to get the locations of the start points, and used NEAR to get the angle between them (from start to end)
I had used Near on selection layers that each only contained one point: each of the matching pair, so there was no confusion about which point pairs I wanted to know about.
From this I recieved an angle, albeit one measured counter-clockwise from the x axis (as NEAR is advertised to deliver).
I subtracted that angle from 90 to get an angle rotated clockwise from the y axis (as I understand BearingDistanceToLine wants).
I had calculated the desired distance in meters earlier.

I used the POINT_X and POINT_Y from AddXY in Stereographic for the origin (and the resulting lines start in the right place, so that is okay)
I used my previously calculated length for the length (this came out fine too)
and I used the 90° - NEAR_ANGLE value for the direction (and this was funky)

I tried using some other angles too. It has since occured to me to try using the same angle for all the points (scattered across the Arctic), but I have not done that yet.
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by Esri Regular Contributor
Esri Regular Contributor
Hi Mark,

I realized that you are expecting the Bearing to be measured clockwise from Y-axis direction, instead of the azimuth north. So here are my thoughts:

1. Even though the tool parameter explanation for Bearing Field states that it is "A numerical field in the input table containing bearing angle values for the output line rotation. The angles are measured clockwise from North", the graphic illustration needs to better clarify that by showing where the north is. Sorry about the misleading information.

2. It is a valid expectation that the tool could support an option for the Bearing values to be measured from the Y-axis. If possible, could you describe what the use case is - what is the theme you are trying to map or the analysis you are trying to do? This information would be helpful in justification for the new option/parameter.

Thank you very much for posting the question and workaround. I will follow up with these enhancements. Let me know if you have further questions or suggestions.
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