On Fri, 30 Jan 2009, Miguel Eduardo Gil Biraud wrote:
Hi, I was going to post a similar question as I am also a fresh new user of R.
This isn't the same question, so the threads are crossed now ...
In my case I have between 10 million and 20 million latitude, longitude pairs and want to get an image in which each pixel has a color that is a function of the amount of positions that would fall into the spatial bin corresponding to the pixel size. I understand that this would be akin to a 2D histogram of my data and resemble a density plot. The way I started doing that was importing the table with read.table() and then converting it to a PPP object providing the adequate bounds. The first problem I face is that when I try to put all the points into the PPP object I get a memory failure. To keep experimenting I lowered the number of points I import and played around with the density function available in spatstat but while I can see its uses when you have few points, in my case the patters would get diluded very fast even for small values of sigma and I am afraid it would not represent the data faithfully. On the other hand the function quadratcount returns very fast results for a high number of partitions in the X and Y axis and I could certainly use the results it provides, if it wouldn't be for the fact that when I try to plot it, I get the grid and the point count inside each cell. Is there any way to convert the output of gridcount into a colored plot in the same spirit of the one you get when you do a plot(density())? Hope it wasn't too confusing. As you can see I've tried to take a jab at it on my own, but it is proving more complicated than I expected! :)
If you simplify, you'll see that all you are trying to do is count points in grid cells. While a quadrat count looks natural, that function is actually used to show why quadrat counts as a method of point pattern analysis are inadequate. My guess is that you should look at the overlay() method for SpatialPoints and SpatialGrid objects in the sp package, which will return a vector showing which grid cell each point belongs to. From there, you can use other functions, for example table(), to tally, then construct a SpatialGridDataFrame.
At your choice, GE_SpatialGrid() in maptools and image() will let you display your output in Google Earth if you choose, image() or spplot() for regular R graphics, or write it out and read into a GIS or paint program with writeGDAL() in rgdal.
Roger
Cheers, Miguel On Fri, Jan 30, 2009 at 06:09, srinivasa raghavan <srinivasrag...@gmail.com> wrote:Hi r-sig-geo team, I am a new user of R 2.8.1 in windows 2003. I have a data set of football ball pattern data. The data is for multiple matches. The variables are : match: The code number of the match. period: First half or second half denotted by 1 or 2. pitchX: The x co-ordinate of the field. pitchy: The y-co-ordinate of the field. seconds: The time point. I am interested to draw the football graph/diagram and then plot the above data. Can any one let me know the right functions/packages which can help me in this regard. thanks in advance. warm regards, srinivas statistical analyst. [[alternative HTML version deleted]] _______________________________________________ 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: roger.biv...@nhh.no _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
