[R-sig-Geo] How do I read/work with PolyLineZM with maptools/sp?

[Roger Bivand]

On Mon, 16 May 2011, Mikhail Titov wrote:

> Edzer:
>
> Thank you for your suggestions, but it doesn't help much. It does not 
> recover either Z or M as attributes or anyhow else.

The Z is dropped for SpatialPolygons and SpatialLines everywhere. The M is 
not a standard part of the specification - it isn't obvious what it should 
be. You'd need to rewrite the C code in shapelib for maptools or rgdal to 
access these, and create a 4D object. Alternatively, try anything perhaps 
in Python with OGR to dump 3D points with M as an attribute, and a 
grouping factor to point to the feature ID in the DBF file.

Roger

>
>> p <- as(s, "SpatialPointsDataFrame")
>> names(p)
> [1] "Id"       "Lines.NR" "Lines.ID" "Line.NR" 
>> slotNames(p)
> [1] "data"        "coords.nrs"  "coords"      "bbox"        "proj4string"
>> head(p at coords)
>     coords.x1 coords.x2
> [1,]  408794.5   4893921
> [2,]  409088.3   4893599
> [3,]  409165.2   4893484
> [4,]  409434.7   4893214
> [5,]  409684.9   4893060
> [6,]  409742.6   4893060
>> head(p at data)
>    Id Lines.NR Lines.ID Line.NR
> 0    1        1        0       1
> 0.1  1        1        0       1
> 0.2  1        1        0       1
> 0.3  1        1        0       1
> 0.4  1        1        0       1
> 0.5  1        1        0       1 
>> p$Z
> NULL
>> p$z
> NULL
>
> I double checked that I'm working with correct shapefile that has Z values.
>
> Mikhail
>
>
>> -----Original Message-----
>> From: Edzer Pebesma [mailto:edzer.pebesma at uni-muenster.de]
>> Sent: Monday, May 16, 2011 1:29 PM
>> To: Mikhail Titov
>> Cc: r-sig-geo at r-project.org
>> Subject: Re: [R-sig-Geo] How do I read/work with PolyLineZM with
>> maptools/sp?
>> 
>> 
>> 
>> On 05/16/2011 08:22 PM, Mikhail Titov wrote:
>> >> I would try s$M and s$Z to access M and Z when they are attributes.
>> > But what do I do when they are not? It can work for points, but not a
>> line as I can't have attributes for individual points of a line. I would
>> prefer not to do any extra conversions in GIS before using R.
>> >
>> 
>> as(s, "SpatialPointsDataFrame")
>> 
>> > Do I get it right that for now it is better to stick with shapefiles to
>> read PolylineZM?
>> >
>> > Mikhail
>> >
>> >
>> 
>> --
>> Edzer Pebesma
>> Institute for Geoinformatics (ifgi), University of Münster
>> Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
>> 8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
>> http://www.52north.org/geostatistics      e.pebesma at wwu.de
>
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, 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