[postgis-users] PointM, PolyLineM, PolygonM

[strk]

pramsey wrote:
> Is is possible to have measure *and* elevation in a shapefile? XYZM? Or 
> is it only XYZ and XYM?
> Paul

I think it is *NOT* possible.

>From the Shapefile Format Specification this is the list of known shapes:
	
	Value   Shape Type
	0	Null Shape
	1    	Point
	3    	PolyLine
	5    	Polygon
	8    	MultiPoint
	11    	PointZ
	13    	PolyLineZ
	15    	PolygonZ
	18    	MultiPointZ
	21    	PointM
	23    	PolyLineM
	25    	PolygonM
	28    	MultiPointM
	31    	MultiPatch

I think using the Z field could be ok, but we need a function that tell
us wheater a geometry is 2d,3d or measured.  Does OGC say anything about
measures ? The array option might also work as a temporary solution, as
would do a just-drop-measure approach.
... shp2pgsql could give a few options (--measured-policy=[array|discard])

--strk;


> 
> Frank Warmerdam wrote:
> > Paul Ramsey wrote:
> > 
> >> Since the measures are a vertex-by-vertex measurement, not a 
> >> feature-by-feature one, they cannot be dropped into an attribute 
> >> table, generally speaking.
> > 
> > 
> > Paul,
> > 
> > But they could be kept in an "array" field, couldn't they?  I realize
> >  this would lose the explicit relationship with the geometry and it
> > might get out of sync if operations were done, but it seems like a
> > cheap way to incorporate the data now.  The loader could give an
> > option to do this, or to insert as the Z coordinate in the geometry.
> > 
> > Best regards,
> > 
> 
> 
> -- 
>        __
>       /
>       | Paul Ramsey
>       | Refractions Research
>       | Email: pramsey at refractions.net
>       | Phone: (250) 885-0632
>       \_
> 
> 
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