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 ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
