ST_WrapX

[strk]

Still looking for a good name, anyway the idea is to allow people to "split" a set of geometries in a table so that every component falling off a given X-value is X-shifted by a given amount. Tipical use is to make a wgs84 map visible as 0,360 rather than -180,180 or as whatever makes sense of a specific use (think pacific).

This was referred to as ST_ShiftLongitude on the mailing list ​http://postgis.refractions.net/pipermail/postgis-devel/2010-February/008886.html

But the "Longitude" part is misleading as it may be useful in mercator too for example..

[strk]

longitudeWrap version

[strk]

I think ST_HWrap is a good name. Now we have a name, half work is done

[strk]

HWrap I still didn't like as it assumes X is horizontal. So it's now called ST_WrapX. The attached version also makes use of the new ST_Split function and calls ST_Union as the last step.

Now it seems a pretty good and complete function to let down to C.

[strk]

I'm on this, will be included in 2.3.0

[strk]

In 14961:

Implement lwgeom_wrapx and ST_WrapX

Includes tests (both cunit and regress) and documentation.

Closes #454

[pramsey]

I'm getting a compile warn on this:

lwgeom_wrapx.c:26:9: warning: 'POSTGIS_DEBUG_LEVEL' macro redefined [-Wmacro-redefined]
#define POSTGIS_DEBUG_LEVEL 4
        ^
./../postgis_config.h:123:9: note: previous definition is here
#define POSTGIS_DEBUG_LEVEL 0

[strk]

I'm actually debugging a crash, so will reopen this until that is fixed.

[pramsey]

Here's another warning for the hopper

lwgeom_wrapx.c:131:14: warning: comparison of unsigned expression >= 0 is always true [-Wtautological-compare]
                        while (--i>=0) lwgeom_free(wrap_geoms[i]);
                               ~~~^ ~
1 warning generated.

[strk]

In 14968:

Fix wrapping of multigeometry elements becoming multi on wrap

Closes #454 again

[strk]

In 14969:

Use int for iterating over geometry index

Avoids a potential infinite loop on split error (see #454)

[strk]

Paul please try with r14969 — we really need to add those compiler flags by default :/

[ see #3037 ]