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

[Roger Bivand]

On Mon, 16 May 2011, Mikhail Titov wrote:

> Roger:
>
> I see. It is not a 5-minute job. I'll leave my script as is with 
> `shapefiles` package for now as it is working okay. I just have a 
> feeling that shapefiles is getting quite outdated (last published in 
> 2006) and overall trend is towards structured sp and maptools.
>
> Thanks for your help! Perhaps one day ZM support will be available in 
> maptools/sp :-)

OGR says that it will not be returned:

http://www.gdal.org/ogr/drv_shapefile.html

>
> P.S. I always thought and used M for route *m*easure data as a distance 
> along the line via `Create Routes` tool in ArcGIS. I don't know how it 
> can be non-standard.

It always was a kludge. I guess that it could once have been intended to 
hold a precision value, but is not used as such systematically. The 
maptools interface could return it, but there is no structure to put it 
in, as it is data at the point level, not the feature level. It is not in 
accord with OGC SFS, I think. It could be an extra function returning any 
such file as a SpatialPointsDataFrame with Z, M, and FID data fields. The 
FID could then be used to link to the data in the DBF.

Roger

>
> P.P.S. I used `Write Features to Text File` with `Samples` toolbox in 
> ArcGIS. However I want to reduce number of steps overall and I thought I 
> could use shapefiles directly. I would do everything in python with 
> arcgisscripting module, but my script depends on `fda` and monotonic 
> splines in R.
>
> Mikhail
>
>
>> -----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 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
>>>
>>> _______________________________________________
>>> R-sig-Geo mailing list
>>> R-sig-Geo at r-project.org
>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>
>> --
>> 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
>
>

-- 
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