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

[Peter Halls]

> 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.

I reported it to  Frank at the time ... but several email systems later, I
no longer have my copies of the correspondence with ESRI nor the OGR bug
report, in which these were copied.  Somewhere I may still have a backup of
my work area, to see what I did in my code.  However, as you say, this is
20+ years ago ....  It was something which, at the time, was causing us
some problems ....

I think you to be correct in your Shapelib summary below:

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




On 10 February 2016 at 12:31, Even Rouault <even.rouault at spatialys.com>
wrote:

> 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
>
> --
> Spatialys - Geospatial professional services
> http://www.spatialys.com
>



-- 
----------------------------------------------------------------------------------------------------------------
Peter J Halls, PhD Student, Post-war Reconstruction and Development Unit
(PRDU),
                      University of York

Snail mail: PRDU, Derwent College, University of York,
                Heslington, York YO10 5DD
This message has the status of a private and personal communication
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