[postgis-users] PostGIS Geography and Rhumb Lines

Paul Ramsey pramsey at opengeo.org
Wed Nov 28 08:47:12 PST 2012

ST_Segmentize in geography will just segmentize along the great
circle. You'll have to choose whether you want your model in geometry
or geography. If geometry, then you can use Mercator as your
projection (rhumb lines are then straight line) and use
ST_Segmentize(geography) to convert your great circles into
approximations in mercator.
Or, you can use geography, and leave your great circle lines alone,
but project your rhumb lines into geometry in mercator, st_segmentize
them *there*, then convert htem back to geography.
Clear as mud?

On Wed, Nov 28, 2012 at 4:33 AM, Sandro Santilli <strk at keybit.net> wrote:
> PostGIS-2.1 (in development) has an ST_Segmentize implementation for
> "geography" type, which should help with rhumb lines.
> You may or may not need to segmentize depending on the operation you
> want to do on those lines. Anyway it would be practical to use in your
> SQL queries if you don't want to store the segmentization persistently.
> --strk;
> On Wed, Nov 28, 2012 at 01:39:09AM -0800, Derek Meyer wrote:
>> My current project involves creating a spatial database of world-wide
>> airspace data, where each known flight information region is a polygon
>> containing boundaries that are a combination of great circle lines,
>> rhumb lines, and arcs.
>> It seems straight forward enough that these polys could be easily
>> inserted into the database via ST_GeographyFromText fed with a WKT
>> GEOMETRYCOLLECTION of these compound boundary types, but I'm wondering
>> about how to deal with rhumb lines in such a case since the Geography
>> functions, if I understand correctly, base everything around a round
>> earth model and utilize great-circle by nature.
>> Is there any way to explicitly declare a rhumb line in an insert query
>> such as this?  I've seen some examples elsewhere where a temporary
>> projection to 2D is utilized and then segmentized to
>> render/interpolate coordinates for a linestring that would more
>> accurately represent said rhumb line.  Is this still the accepted
>> approach?  Practical?  If so, how would such an approach be
>> implemented in context of the SQL query?
>> Any info/suggestions welcome and appreciated.
>> Thank you for your time,
> _______________________________________________
> postgis-users mailing list
> postgis-users at lists.osgeo.org
> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users

More information about the postgis-users mailing list