[postgis-users] PointM, PolyLineM, PolygonM, ...

[strk at refractions.net]

On Thu, Sep 23, 2004 at 02:14:10PM +0200, Pierrick Brihaye wrote:
> Hi again,
> 
> strk at refractions.net a écrit :
> 
> >I'm with you,
> 
> Great !
> 
> >but quetions are:
> >
> >1) how should we import TypeM shapefiles ?
> >	a) as x,y,Z,m // wasting Z space in postgis 
> >	b) as x,y,z   // interpreting M as Z
> 
> I vote for a).
> 
> I don't know if it is a "waste" though :-)

Well.. it would contain 0.0 values for each point...

> 
> >2) how should we import TypeZ shapefiles ?
> >	a) as x,y,z,m // respecting shapefile meanings 
> >	b) as x,y,z,m // swapping M<->Z meaning
> 
> I think you mean :
>  	b) as x,y,m,z // swapping M<->Z meaning

correct.

> 
> >	c) as x,y,z   // discarding M
> >	d) as x,y,z   // using M, discarding Z
> 
> I vote for a)
> 
> >3) how should we export geometry3d ?
> >	a) as TypeM // using M for Z values
> >	b) as TypeZ // wasting M space in shapefile
> 
> I vote for b) Let ESRI files carry the waste :-))
> 
> >3) how should we export geometry4d ?
> >	a) as TypeZ // respecting shapefile meanings (4th dim -> M)
> >	b) as TypeZ // swapping M<->Z meaning
> 
> I vote for a)

Ok. So your vote is: respect semantics, even if it's a waste of space.

> BTW : how would you consider a missing Z coordinate ? A "null" (i.e. 
> "not applicable") behaviour would be very nice, but wouldn't it make the 
> stuff more complicated ?

I guess you mean a missing M coordinate...
I'm afraid it'll have to be 0.0 as NaN coordinates are invalid.

--strk;

> 
> Best regards,
> 
> -- 
> Pierrick Brihaye, informaticien
> Service régional de l'Inventaire
> DRAC Bretagne
> mailto:pierrick.brihaye at culture.gouv.fr
> +33 (0)2 99 29 67 78
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