Roger Bivand <[EMAIL PROTECTED]> wrote:
> > I don't mean to rant, but believe me, I've spent plenty of time with > > the documentation and it's really not helping. > > > > Partly this is a problem of R's doc format which treats package > > documentation as an alphabetical list of functions - which gives me no > > idea where to start. I would tend to second this. I've been lurking on the list for a few months, hoping to learn a bit, but so far without much success, since the conversation and the documentation are so far above where I am and what I need. I am almost familiar with R, using it for time-series statistics, and learned early on that the Dalgaard book was a better intro than any of the real R documents. It doesn't cover nearly everything, but it seems to cover what I needed, so I use what is probably a baby-level set of R functions, but it's adequate. Without a professor lurking over my shoulder to explain stuff, I am perpetually slightly lost, because all the documentation assumes I know stuff that I don't. I still use R because I know that with enough poking around it will eventually provide a solution. But if the alternatives were not very expensive, I would have given up a while ago. I joined this group when I wanted to expand into making maps of geographical economic data, and after a month of working on the problem, I essentially had to give up for the time being. I wish there were an introduction that showed me how to use R with a GIS program, but to my knowledge, there is not. I did run across a GRASS book that claimed it would help, but as I recall, it cost upward of US$100. To make this more useful than just a rant, I would second David's point. What is missing is only what David misses: an introduction that says where to start to deal with simple geographic data, maybe providing a few examples of common techniques and frequent problems, and pushing data back and forth to some GIS. I was not able to find that, and without it, found the R documentation pretty much useless. I'd be happy to know of some source I hadn't found before, so if you have one to recommend, please do. -tom > > This is an inherent (and perhaps ugly) characteristic of the S4 > object/class structure as you suggest below. New style classes are not > as well integrated into the documentation as straight functions > are. Here, coerce is as(), but the issue of how to improve > documentation is not resolved. > > > > > This then interacts badly with the OO structure. For example, look at > > the 20+ pages on "coerce". Hmm, what does "coerce" actually do? In > > fact that's in a whole different library. But I didn't know that, so I > > click on a page at random, say > > > > coerce,SpatialGrid,data.frame-method > > > > and this takes me to SpatialGrid class - which doesn't mention coerce > > at all. (Nor does it tell me what SpatialGrid is, or what it is used > > for.) > > > > On the other hand, maybe I might guess that to get a list of > > coordinates, I'd use "coordinates". So I click on that method, and it > > tells me yes, this "retrieves spatial coordinates". But unfortunately > > it retrieves them hidden inside another object ("an object of class > > SpatialPointsDataFrame"). OK, but how do I get the _actual_data_? > > Maybe the SpatialPointsDataFrame class page will tell me. Nope. Et > > cetera. > > > > Rick: yes, I agree that using the internal data structures is how to > > do things, but this is broken isn't it? The whole point of having OO > > is to be able to use it _without_ understanding the internal data > > structures. The ideal, in other words, would be to have a "thin.lines" > > method that I could just run on any polygon or set of polygons. > > Failing that, then I should be able to get at the internal data > > without hours of head scratching. > > > > No, because the underlying understanding of dp and other methods for > thinning is that the objects implement an arc-node topological model, > so that each arc can be thinned without different thinning happening > on otherwise identical boundaries of neighbouring polygons. But we do > not have an arc-node representation, so there cannot be line thinning > for polygon boundaries in a spaghetti world. > > > Right now, it's like, everything is hidden behind a layer of classes > > and slots and methods, but I still need to go behind that layer to get > > at the actual raw data, and this is so complicated and confusing that > > it would be easier just to work with the raw data. > > > > You need to build topology first, so if need be take the data out to a > GIS that does topology properly, do the arc line thinning there, and > bring it back in. Building topology from a stream of straight line > segments is a serious challenge, especially if you want to retain the > association with attribute data. > > Roger > > > OK, I'll stop venting. If there's anything I could do to improve this > > situation, I would gladly try. > > > > David Hugh-Jones > > PhD Candidate > > Essex University Department of Government > > http://davidhughjones.googlepages.com > > > > > > 2008/6/30 Virgilio Gomez-Rubio <[EMAIL PROTECTED]>: > >> Dear David, > >> > >> Probably the best way to start is by checking the HTML documentation. It > >> should be installed locally but it is also accesible, for example, here: > >> > >> http://finzi.psych.upenn.edu/R/library/sp/html/00Index.html > >> > >> Hope this helps. > >> > >> Virgilio > >> > >> On Mon, 2008-06-30 at 18:48 +0200, David Hugh-Jones wrote: > >>> Thanks David for his comment about dp. > >>> > >>> Quick question: is there any reasonably comprehensible API > >>> documentation for the "sp" package? I have just spent about an hour > >>> trying to get a list of points from a SpatialPolygons object. I > >>> eventually just printed everything out and found the data by hand, so > >>> now I am doing: > >>> > >>> coords <- [EMAIL PROTECTED]@[EMAIL PROTECTED] > >>> > >>> but I don't assume that is right. Surely there must be some simple way > >>> to get a list of x and y coords out of any object? > >>> > >>> in frustration, > >>> David Hugh-Jones > >>> PhD Candidate > >>> Essex University Department of Government > >>> http://davidhughjones.googlepages.com > >>> > >>> > >>> 2008/6/30 David PINAUD <[EMAIL PROTECTED]>: > >>>> maybe you can try the function dp() in the package "shapefiles", which > >>>> is an > >>>> implementation of the Douglas-Peucker polyLine simplification algorithm. > >>>> Hope it helps > >>>> David > >>>> > >>>> David Hugh-Jones a écrit : > >>>>> > >>>>> Hi all > >>>>> > >>>>> I have a big dataset of points and am doing stuff on them that takes a > >>>>> lot of time. To speed it up, I would like to use "thinlines" from > >>>>> RArcinfo, which basically makes the maps "rougher" by throwing away > >>>>> points. Is there an equivalent function for SpatialPolygon type > >>>>> objects? (I assume that there's no way to convert _to_ Arcinfo, though > >>>>> I know it's possible to read from it). > >>>>> > >>>>> Cheers > >>>>> > >>>>> David Hugh-Jones > >>>>> PhD Candidate > >>>>> Essex University Department of Government > >>>>> http://davidhughjones.googlepages.com > >>>>> > >>>>> _______________________________________________ > >>>>> R-sig-Geo mailing list > >>>>> R-sig-Geo@stat.math.ethz.ch > >>>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo > >>>>> > >>>>> > >>>>> > >>>>> > >>>> > >>>> -- > >>>> *************************************************** > >>>> David PINAUD > >>>> Ingénieur de Recherche "Analyses spatiales" > >>>> > >>>> Centre d'Etudes Biologiques de Chizé - CNRS UPR1934 > >>>> 79360 Villiers-en-Bois, France poste 485 > >>>> Tel: +33 (0)5.49.09.35.58 > >>>> Fax: +33 (0)5.49.09.65.26 > >>>> http://www.cebc.cnrs.fr/ > >>>> > >>>> *************************************************** > >>>> > >>>> > >>>> > >>>> > >>>> ________ Information from NOD32 ________ > >>>> This message was checked by NOD32 Antivirus System for Linux Mail > >>>> Servers. > >>>> http://www.eset.com > >>> > >>> _______________________________________________ > >>> R-sig-Geo mailing list > >>> R-sig-Geo@stat.math.ethz.ch > >>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo > >> > >> > > > > _______________________________________________ > > R-sig-Geo mailing list > > R-sig-Geo@stat.math.ethz.ch > > 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: [EMAIL PROTECTED] > _______________________________________________ > R-sig-Geo mailing list > R-sig-Geo@stat.math.ethz.ch > https://stat.ethz.ch/mailman/listinfo/r-sig-geo -- ------------------------ tomfool at as220 dot org http://sgouros.com http://whatcheer.net _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo