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.
Best wishes,
Peter
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