[postgis-tickets] [PostGIS] #4880: ST_Azimuth with geography type returns incorrect value

[PostGIS]

#4880: ST_Azimuth with geography type returns incorrect value
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 Reporter:  francoisb  |      Owner:  pramsey
     Type:  defect     |     Status:  new
 Priority:  medium     |  Milestone:  PostGIS 3.1.2
Component:  postgis    |    Version:  3.1.x
 Keywords:  angle      |
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 It seems #4718 is a regression.

 Perfect west 270° (3π/2 rad) - the only value in the regression test from
 tickets.sql which had a negative result in the previous code - is by
 chance correct, but all other expected results in the range 180°-360°
 (π-2π rad) are incorrect.

 Second, a perfect north (value exactly 0) is now incorrectly returned as
 180° (π rad), instead of 0.

 The fix is simple. Expected formula in lwgeodetic.c line 2180 is:

 {{{
         return az < 0 ? az + 2.0 * M_PI : az;
 }}}

 instead of:

 {{{
         return az > 0 ? az : M_PI - az;
 }}}

 Regression test from tickets.sql should add additional values, say at 45°
 (Northeast, π/4) and at 315° (Northwest, 7π/4).

 Documentation for ST_Azimuth could be extended to read:

 North = 0; Northeast = π/4; East = π/2; Southeast = 3π/4; South = π;
 Southwest 5π/4; West = 3π/2; Northwest = 7π/4

 instead of:

 North = 0; East = π/2; South = π; West = 3π/2

-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/4880>
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