How do I read/work with PolyLineZM with maptools/sp?

-----Original Message-----
From: Roger Bivand [mailto:Roger.Bivand at nhh.no]
Sent: Monday, May 16, 2011 1:59 PM
To: Mikhail Titov
Cc: 'Edzer Pebesma'; r-sig-geo at r-project.org
Subject: Re: [R-sig-Geo] How do I read/work with PolyLineZM with
maptools/sp?

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 M?nster
Weseler Stra?e 253, 48151 M?nster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
http://www.52north.org/geostatistics      e.pebesma at wwu.de

--
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