[R-sig-Geo] wkbMultiPoint and rgdal

Michael Sumner mdsumner at gmail.com
Sat Jul 30 02:13:24 CEST 2011

This is a fundamental philosophical point that I haven't seen made
explicitly before, and I appreciate hearing it and I'm sorry if I've
missed it being laid out previously.

There is another example, similar (I think) to the multipoint one
(you'll find an implementation of multipoint inheriting from lines in
the ASDAR book btw, similar to how 'polygons' inherit from lines in
almost all software I am aware of).

sp's data structures purposely do not support the Z attribute on
vertices either, let alone the M one. If it were up to me I would
stick to the the GDAL/OGR (or OGC model) and let users take the
responsibility of what sense it makes. Points and lines present
absolutely no topological problems for n-dimensional geometry -
polygons do but that's because they are not true 2D topology.

I work in data transfer far more than I do in statistical analytics so
I guess that is mainly where the difference in perspective comes from.
I've come close to being able to modify the designs to do things how I
would like but it's mostly beyond me, I'm not complaining I wish I had
the skills to branch and write my own versions.

Cheers, Mike.

On Fri, Jul 29, 2011 at 5:57 PM, Roger Bivand <Roger.Bivand at nhh.no> wrote:
> On Thu, 28 Jul 2011, Jonathan Greenberg wrote:
>> Hi Dylan:
>> Thanks -- I'm a bit of a PostGIS noob so I ended converting it to a
>> normal point file with the XTools extension in Arc.  I'm surprised
>> there is no support for this data type in any R package, since I would
>> think it is a fairly common type.  Ah well!
> Jonathan,
> Not really, as this is the first time I can recall it being mentioned in 8
> years. It is far from obvious what one could do with it that couldn't more
> properly be done with a SpatialPointsDataFrame with a grouping factor. What
> is the implied support of the data? What are the attributes attached to -
> say var1 was observed at which of the member points? All of them
> simultaneously? If they form a line or polygon, then support is clear(er),
> but if a multipoint observation is better handled as described above, then
> it should be. Support is absolutely crucial for clarity in analysis (and
> visualization), I think.
> Roger
> PS: this is a similar case to that of the unusual M coordinate in some
> shapefiles - if it cannot be shown how this relates consistently to support,
> it shouldn't be admitted, I think. If we lose clear understanding of support
> for observation attributes, we cease to be able to interact with
> statisticians, and that interaction really matters.
>> --j
>> On Tue, Jul 26, 2011 at 2:28 PM, Dylan Beaudette
>> <dylan.beaudette at gmail.com> wrote:
>>> Hi Jonathan,
>>> My tool of choice for this operation is PostGIS. If you happen to have
>>> a postgis db ready to go, simply import your problem file using the
>>> postgis shapefile import tool and process there. Some tips here:
>>> http://amercader.net/blog/2011/04/exploding-multigeometries-with-postgis
>>> Cheers,
>>> Dylan
>>> On Tue, Jul 26, 2011 at 2:13 PM, Jonathan Greenberg
>>> <greenberg at ucdavis.edu> wrote:
>>>> R-sig-geo'ers:
>>>> I have an ESRI shapefile which has multi-point geometry, and I'm
>>>> trying to get it into R for use with sp() and raster().  Using:
>>>> points=readOGR(dsn=getwd(),layer="tnf_sub_2_TreeDig_pts_110725_v02")
>>>> returns:
>>>> Error in readOGR(dsn = getwd(), layer =
>>>> "tnf_sub_2_TreeDig_pts_110725_v02",  :
>>>>  Incompatible geometry: 4
>>>> In addition: There were 50 or more warnings (use warnings() to see the
>>>> first 50)
>>>> the warnings all say:
>>>> ...
>>>> 50: In readOGR(dsn = getwd(), layer =
>>>> "tnf_sub_2_TreeDig_pts_110725_v02",  ... :
>>>>  eType not chosen
>>>> What I really want is to, in the end, have a SpatialPointsDataFrame
>>>> where each multi-point feature is converted to individual points that
>>>> have the attribute of what multi-point feature it came from.  What is
>>>> the best way to do this?  I'm attaching the zipped shapefile to this
>>>> email (hopefully it won't get bounced).
>>>> --j
>>>> --
>>>> Jonathan A. Greenberg, PhD
>>>> Assistant Project Scientist
>>>> Center for Spatial Technologies and Remote Sensing (CSTARS)
>>>> Department of Land, Air and Water Resources
>>>> University of California, Davis
>>>> One Shields Avenue
>>>> Davis, CA 95616
>>>> Phone: 415-763-5476
>>>> AIM: jgrn307, MSN: jgrn307 at hotmail.com, Gchat: jgrn307
>>>> _______________________________________________
>>>> R-sig-Geo mailing list
>>>> R-sig-Geo at r-project.org
>>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> --
> Roger Bivand
> Department of Economics, NHH Norwegian School of Economics,
> Helleveien 30, N-5045 Bergen, Norway.
> voice: +47 55 95 93 55; fax +47 55 95 95 43
> e-mail: Roger.Bivand at nhh.no
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at r-project.org
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Michael Sumner
Institute for Marine and Antarctic Studies, University of Tasmania
Hobart, Australia
e-mail: mdsumner at gmail.com

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