[R-sig-Geo] Re: [R] writing polygons/segments to shapefiles (.shp) or other ArcGIS compatible file

[Patrick Giraudoux]

Hi,

Thanks for all those information and the most valuable library you have developed.

If somebody is to develop something to write shapefiles from polygon coordinates within R (most welcome), I don't think that the
attribute file (dbf) will be an important issue. If we have got an output with the index to link the dbf records to each shape of a
shapefile, any text file can be handled in R or Excel to create a dbf. The real issue is the encoding of the *.shp and *.shx  etc..
(and an index file for the dbf)

Most important is to consider that ESRI has stopped developping ArcView and AVENUE. They have moved to ArGIS and Visual Basic. In
this new generation framework, importation is managed with ArcToolBox which, to my knowledge, is very limited considering
importation of text objects (actually I even wonder if one can import something but attribute tables without ArcInfo). For instance,
the way I found to solve the problem I met was to write a programme in R to wrap the polygon coordinates in a text file readable in
GRASS (an opensource GIS), to import it into GRASS and to export the shapefile from GRASS. This shapefile was finally imported to
ArcGIS.  I would not insist on ESRI client policy. I just want to say that the more I know corporates the more I love opensource...

Anyway, there are many things that can be made in R which may deserve not only importation to R, but also exportation to many kinds
of GIS. To write shapefiles from polygon, points or lines created in R would be most useful.

Many thanks for your interest and support,

Patrick Giraudoux


Université de Franche-Comté
Laboratoire de Biologie environnementale
EA3184 usc INRA
F-25030 Besançon Cedex

tél.: +33 381 665 745
fax.: +33 381 665 797
http://lbe.univ-fcomte.fr

"Ce n'est pas en améliorant la bougie que l'on a inventé l'électricité", la recherche fondamentale est indispensable !




----- Original Message ----- 
From: <Benjamin.STABLER at odot.state.or.us>
To: <patrick.giraudoux at univ-fcomte.fr>
Cc: <r-help at stat.math.ethz.ch>; <r-sig-geo at stat.math.ethz.ch>
Sent: Thursday, February 26, 2004 7:11 PM
Subject: Re: [R] writing polygons/segments to shapefiles (.shp) or other ArcGIS compatible file


> The main limitation of the shapefiles package that I put together is that it
> does not create shapefiles from R objects - rather it only writes shapefiles
> that have been read into R and manipulated within the constraints of the
> existing file structure.  By this I mean that for example you can change the
> coordinates of points and write them back out.  Or you can add a bunch of
> blank columns in the DBF outside of R and then fill them in with R.  But I
> did not write any code to calculate byte offsets and such and that are
> needed when creating a shapefile from scratch.
>
> So what I do when I want to create a new shapefile from within R is write
> out the format required by the ASCII Tool ArcView (Avenue) script.  This
> script is available at: http://arcscripts.esri.com/details.asp?dbid=11442
> The format is simple:
>
> Works for space delimited ascii to point, polygon and polyline. The format
> for point ascii file is id, x, y (no comma for real data, space delimited).
> For polygon & polyline ascii files, the format is code (1 for start point, 2
> for middle points, 3 for end point), x, y (no comma for real data, space
> delimited). Export shapefile to ascii file works for point, polyline and
> polygon shapefiles. The output format file is id, x, y. For polygon and
> polyline, the id is the sequence id of vertices.
>
> Thus all you have to do is write a text file, install the script in ArcView
> and then use the ArcView extension to create a shapefile from the ASCII
> file.  Unfortunately ASCII tool only works with the geography - you have to
> add the attributes later.
>
> With all of that said, I would like to add to the shapefiles package the
> ability to write out shapefiles from scratch.  Since the shapefiles format
> is rather unique, I think it would be best to use the maptools ShapeList/Map
> class format (or r-spatial's classes).  For starters the package would just
> write out the geography (like the ASCII tool Avenue script).  Later would be
> added the ability to write the dbf data out from the att.data element of the
> Map object.
>
> Unfortunately I don't know when I will have the time to do this.  If anyone
> else wants to do then please go ahead and I can help via email if needed.
> But adding the ability to write out shapefiles from scratch is on my list.
> Once I finish coding our travel demand model and we enter the application
> phase (probably in a few months) then will our demand to output shapefiles
> from R increase and I can justify spending the time to write the code.
>
> I apologize that I have not paid much attention to the r-sig-geo discussion
> or Edzer's r-spatial project.  If there is an effort underway to write out
> shapefiles then can someone please inform me of its status.  If not, then
> maybe I can help.  Thanks.
>
> Benjamin Stabler
> Transportation Planning Analysis Unit
> Oregon Department of Transportation
> 555 13th Street NE, Suite 2
> Salem, OR 97301  Ph: 503-986-4104