[R-sig-Geo] create a 3d shapefile ?

[Agustin Lobo]

Actually my current need is writing aerial waypoints as gpx files with
x,y,z to be used in the field with a gps program
(ie. oruxmaps) for an android tablet.
I do create the waypoints in R (as I plan the campaign with R), so my
problem is not reading 3d shapefiles, but writing the 3d waypoints
either to gpx directly
or to shapefile and then convert to gpx with i.e. gpsbabel.
My understanding is that rgdal/sp cirrently support reading 3d
shapefiles but not actually writing 3d spatial points DF

Agus

On Mon, Mar 18, 2013 at 8:54 AM, Michael Sumner <mdsumner at gmail.com> wrote:
> It's actually something I have long wanted to explore, but rgdal source is
> still out of reach to me (just need to spend enough time). I think it would
> be useful to read and write 3 and possibly 4-d objects, and apart from the
> class validation and read/write this is possible for points and lines if
> you generalize bbox. It would obviously break for a lot of downstream uses
> of sp though.
>
> Reading from shapefiles with Z would be enough for a lot of things, perhaps
> it's worth chasing that and making a special class that won't break
> anything else (Roger Bivand explained this offlist some time ago, and I can
> do that but it's the read I want to figure out myself).  But, it has been a
> long time since I compiled rgdal so even simple exploration is a way off
> for me.
>
> Note that polygons in OGC are composed of linear rings and so unless your
> polys are composed completely of individual triangle facets they are rarely
> going to be of any use. Lines are much simpler but still pose complications
> for validation in 2d (think of intersecting lines) compared to 3d or higher.
>
> As a workaround you can use gdal to extract the data to something more
> generic, as here
> https://stat.ethz.ch/pipermail/r-sig-geo/2009-November/006866.html
>
>
> Cheers, Mike
>
>
>
> On Monday, March 18, 2013, Agustin Lobo wrote:
>
>> Thanks, this is what seemed to me, but the following phrase from the sp pdf
>> "The classes document where the spatial location
>> information resides, for 2D or 3D data"
>>
>> and some scattered info such as
>>
>> http://gis.stackexchange.com/questions/43342/how-to-use-z-coordinate-in-qgis
>>
>> http://grokbase.com/t/r/r-sig-geo/127s88jzc6/problem-extracting-z-value-from-line-shapefile
>>
>> make me think that some support for x,y,x coordinates actually exists
>> in sp and perhaps writeOGR() could
>> have taken advantage of it.
>>
>> I've got very good advice on how to create the 3d shapefiles using
>> simple python scripting in the qgis list, I insert the link:
>>
>> http://osgeo-org.1560.n6.nabble.com/create-3d-shapefile-and-or-GPX-tp5040855p5040863.html
>>
>> Agus
>>
>> On Sat, Mar 16, 2013 at 2:00 PM, Michael Sumner <mdsumner at gmail.com>
>> wrote:
>> > It is not possible.
>> >
>> > Cheers, Mike
>> >
>> > On Saturday, March 16, 2013, Agustin Lobo wrote:
>> >
>> >> Is it possible to write point ESRI shapefiles with x,y,z
>> >> coordinates using writeOGR()?
>> >> According to what I've been able to find, it seems
>> >> that spatial points can have 3 coordinates while
>> >> spatial lines cannot. Nevertheless, coordinates() accepts
>> >> 2 arguments (x,y) only. So actually, do not know how to define
>> >> x,y,z coordinates for spatial points (data frame) objects.
>> >> Is it possible?
>> >>
>> >> Thanks,
>> >>
>> >> Agus
>> >>
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>> >
>> >
>> > --
>> > Michael Sumner
>> > Hobart, Australia
>> > e-mail: mdsumner at gmail.com
>> >
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>
>
> --
> Michael Sumner
> Hobart, Australia
> e-mail: mdsumner at gmail.com
>
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