> 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.roua...@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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