NO Dear list-serve, Thanks in advance to all those who help out with the inquiries, it is has helped me numerous times. Here go my questions...
I am trying to vary existing landscapes which are composed of habitat (patches) and non-habitat. My goals are to vary the number of patches in a landscape, and the size of each patch. My landscape files are originally raster files, which I have converted to ascii format. When importing into R, they are of class SpatialGridDataFrame, are fully gridded. Each cell is represented by a 0: non-habitat, or a value ranging between >0 and <=1, which represents varying degrees of habitat quality. Patches are simply identified where adjoining cells are >0. The approach I have taken is to create a mask of my ascii landscape file so that already existing patches are masked. This allows me to sample a point in the region of my landscape that is identified as non-habitat. I then apply the dilate function to essentially 'grow' a patch. I have followed the code from the following link: http://finzi.psych.upenn.edu/R/Rhelp02a/archive/115868.html The only difference is that once I have effected the dilate function, which is of class 'owin', I then: 1) coerce "owin" to "im" object class 2) coerce "im" object class to a SpatialGridDataframe My problems are: 1. How to overlay my final 2 layers: 1) dilated object (object class SpatialGridDataFrame) and 2) original landscape patch layer (also object class SpatialGridDataFrame). I need the resulting object to be an object of class SpatialGridDataFrame with only 1 band consisting of original patches, the new patches, and non-habitat so I can perform additional data manipulations. The overlay function does not appear to work with 2 objects of this class. Any alternative suggestions? 2. My dilated points object (SGDF) does not have topology identical to the original layer - I think I need them to be the same for the overlay process, and if yes, how do I change this. The cell size remains the same but the offset and cell dimension are not identical. For example: > getGridTopology(dilate_SGDF) X1 X2 cellcentre.offset 1050 890 cellsize 20 20 cells.dim 15 11 > getGridTopology(original_layer) x y cellcentre.offset 1030 870 cellsize 20 20 cells.dim 16 12 3. I would like to sample on the patch edge and use the dilate or erode functions to increase or decrease the size of a patch. How can I force the sampling of a spatial point, which becomes the centre for the dilate/erode function, to fall on a patch edge. In other words, if I was to look at the landscape file in ascii format I would need to sample a grid cell that has a value of >0, but where at least 1 of the cells surrounding this point, in all orthogonal directions, has a value = 0. 4. How to constrain the newly added patches so that they does not overlap with existing patches. 5. How to add patches of different sizes -perhaps I can simply add a loop to my code? I am using Windows XP and R.2.6.1. Any help on these issues would be greatly appreciated. Thanks in advance for your help on these multiple but related issues. I do appreciate the time that people take in responding to these inquiries. Best, ilona Ilona Naujokaitis-Lewis Centre for Applied Conservation Research Forest Sciences Department University of British Columbia 3041-2424 Main Mall Vancouver, BC V6T 1Z4 phone: 604 822.4382 email: [EMAIL PROTECTED] _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
