[postgis-devel] measures test fail

[Nicklas Avén]

It seems like m and z snapping is implemented  at the "version 4" (in
doc) of the function, when a point is used to define the origin of the
grid cell. Bu tin the more common ST_Snaptogrid(geometry, size_of_grid)
there is no snapping to m and z.

In lwgeom_functions_analytic.c there is a comment on line 790

	/* Do not support gridding Z and M values for now */
	grid.ipz=grid.ipm=grid.zsize=grid.msize=0;


The problem now if we want those other version to also snap z and m is
that we will have to mess up the order of arguments in some way.

In the documentation
http://postgis.org/documentation/manual-1.5/ST_SnapToGrid.html

The version of the ordinary snaptogrid function with all arguments 
have this form:
ST_SnapToGrid(geometry geomA, float originX, float originY, float sizeX,
float sizeY);

so, where to put z and m arguments?
to not change the old ones we have to put them in the end. But to follow
the form from before we out to have the originZ and originM before,
sizeX

Any ideas?

/Nicklas




On Mon, 2010-10-18 at 17:39 +0200, strk wrote:

> On Mon, Oct 18, 2010 at 03:42:58PM +0200, Nicklas Avén wrote:
> > Hallo Sandro
> > 
> > I was about to do the same a few weeks ago when I realized that
> > snaptogrid is only workin in 2 dimensions now. 
> > 
> > I think we said then we should open up for the third dimension in
> > snaptogrid to. As I understand it it is all prepared (you are the author
> > aren't you :-)  ). I have not looked at it since the discussion on the
> > list a few weeks ago, but maybe it is easier and faster for you to open
> > up for 3D snapping. 
> 
> Seems like done already, from postgis.sql.in.c:
> 
> -- SnapToGrid(input, point_offsets, xsize, ysize, zsize, msize)
> -- Availability: 1.2.2                                                          CREATE OR REPLACE FUNCTION ST_SnapToGrid(geometry, geometry, float8, float8, float8, float8) AS 'MODULE_PATHNAME', 'LWGEOM_snaptogrid_pointoff'
>         LANGUAGE 'C' IMMUTABLE STRICT;
> 
> Does up to 4d..
> 
> --strk;
> 
>   ()   Free GIS & Flash consultant/developer
>   /\   http://strk.keybit.net/services.html
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