geodesicUtils.geodesicDistance azimuth and reverse azimuth almost equally

[SebastianKrings]

Hi,

I am using geodesicUtils.geodesicDistance but always getting pretty similar values for azimuth and reverse azimuth.

This is how I call the distance calculation of the geodesicUtils:

const bearing = geodesicUtils.geodesicDistance(

                point1Wgs84,

                point2Wgs84,

                "kilometers"

            );

This is how a result looks like:

z {distance: 61.525187404214556, azimuth: 90.42038020754926, reverseAzimuth: 91.18218544411303}

While the azimuth looks good (that was a line from west to east), the reverse azimuth is almost the same value.

From what I understood I expected the reverse azimuth to be about 270° instead.

When drawing a line from south to north, the azimuth is abut 0-1° and reverse azimuth too, which I would expect to be about 180° instead.

Can anyone help me with these struggles?

[JoelBennett · Accepted solution]

This may be a bug in the SDK.  One might expect the algorithm to calculate the azimuth first, and then calculate the reverse azimuth off of that value by simply adding or subtracting 180 (depending on whether the calculated azimuth is less than 180 or not, respectively), but that's definitely not the case here, because the SDK is calculating them independently of each other (for the most part).

Since it appears the azimuth value is correct, you can just fix the reverseAzimuth value manually after the fact:

const bearing = geodesicUtils.geodesicDistance(point1Wgs84, point2Wgs84, "kilometers");

//fix the reverseAzimuth value
bearing.reverseAzimuth = ((bearing.azimuth >= 180) ? bearing.azimuth - 180 : bearing.azimuth + 180);

[SebastianKrings]

Yeah exactly, the difference should be 180°.

Not great that it is a bug, but knowing it is a bug is great.
Thanks. 

[JesseCloutier]

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