Spheroid/Ellipsoid projection given Lat/Lon, Distance & Bearing

[lwilmen]

Feature request to expose spheroid_project() from liblwgeom as an SQL function to enable projecting from a give lat/lon by a specified heading/distance (metres).

[realityexists]

Please, please implement this for 2.0.0, along with closely related ticket 1305!

I'm currently in the process of implementing these in SQL and, being new to GIS, may waste a lot of time and not do it 100% correctly. A native PostGIS implementation would really help. This has been requested several times on the mailing list, so I think I'm not alone in needing it:

​http://postgis.refractions.net/pipermail/postgis-users/2010-October/027906.html ​http://postgis.refractions.net/pipermail/postgis-users/2010-November/028116.html ​http://postgis.refractions.net/pipermail/postgis-users/2011-May/029749.html

[pramsey]

Committed at r8495

[realityexists]

Thanks! I tried out the new ST_Project function in r8577 together with ST_Azimuth. If ST_Azimuth is changed to return radians (consistent with the geometry overload) then I think ST_Project should also take a bearing in radians. Either way, would be nice to explicitly document it, eg. "The distance is given in meters and the azimuth in ...".

A few other issues:

1) ST_Project can return a point outside of the (-180,180) range, which then fails when passed to other functions, eg.

SELECT ST_Project('POINT(175 10)'::geography, 2000000, 90)

=> POINT(193.223435218359 9.50463611585127)

SELECT ST_AsText(ST_Project('POINT(175 10)'::geography, 2000000, 90))::geography

=> ERROR: Coordinate values are out of range [-180 -90, 180 90] for GEOGRAPHY type

2) SELECT ST_Distance(ST_Project('POINT(10 10)'::geography, 10, 0), 'POINT(10 10)'::geography)

=> ERROR: gbox_overlaps: cannot compare geodetic and non-geodetic boxes

3) ST_DWithin doesn't work with the returned point. SELECT ST_DWithin(ST_Project('POINT(10 10)'::geography, 2000, 90), 'POINT(10 10)'::geography, 2000)

=> false

SELECT ST_DWithin(ST_AsText(ST_Project('POINT(10 10)'::geography, 2000, 90))::geography, 'POINT(10 10)'::geography, 2000)

=> true

[pramsey]

Oops, am I exposing radians? I want to only work with degrees at a user level. Sound good? And looks like ST_Project needs to normalize the outputs before returning.

[pramsey]

Should be better at r8655

[realityexists]

Just noticed that the manual page for ST_Project still uses degrees in examples, even though the function now takes radians for the azimuth.

[michischolz]

Please update the documentation for ST_Project. It sais nothing about how to pass the azimuth and as said before, the example is still showing degrees instead of radians.

[robe]

fixed

for PostGIS 2.1 at r11026 : ​http://postgis.net/docs/manual-dev/ST_Project.html

for PostGIS 2.0 at r11027 : ​http://postgis.net/docs/manual-2.0/ST_Project.html

The changes should update on website shortly so check back if you don't see them and let us know if it still needs further clarification.

[robe]

fixed my misspelling of degrees at r11028 and r11029