[gdal-dev] RFC 61: Call for vote on adoption

[Even Rouault]

Le mercredi 10 février 2016 13:05:20, Peter Halls a écrit :
> Ari, et al,
> 
>       ESRI handle this in a non-intuitive way:  XYM is supported, but Z
> always has a Measure, so is XYZM!   The formal definition is here:
> https://www.*esri*.com/library/whitepapers/pdfs/*shapefile*.pdf   (1998)
> 
>       Shape Types having Z are defined on pp19ff where it states:
> 
> "Shape Types inX,Y,Z Space
> Shapes of this type have an optional coordinate
> M. Note that "no data" value can be specified as a value for M (see Numeric
> Types on page 2).
> PointZ
> A PointZ consists of a triplet of double-precision coordinates in the order
> X, Y, Z plus a measure"
> 
> I had misinterpreted their meaning of "optional" here and submitted a
> documentation query to ESRI on being told I was wrong.  The response was
> that M being optional means that it can be valueless, but is always
> present.

Woo, really ???? That's a genuine scoop.

Unless I'm seriously mistaken, shapelib / OGR has produced XYZ shapefiles 
without M values for more than 20 years. I'm surprised we wouldn't have heard 
about that if such shapefiles couldn't be read. Or perhaps ESRI software is 
robust to missing M too

> 
> Best wishes,
> 
> Peter

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