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

Peter Halls p.halls at york.ac.uk
Wed Feb 10 04:05:20 PST 2016

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).
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.

Best wishes,

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