[R] Matrix or grid conversion of spatial data

ONKELINX, Thierry Thierry.ONKELINX at inbo.be
Fri Apr 20 12:02:37 CEST 2007


I've done something similar with spatial data. I defined the points as
SpatialPoints, the grid as SpatialGrid (using the "sp" package). Then
table(overlay(grid, points)) will give you the number of points inside
each gridcell.

points <- SpatialPoints(your.data.frame)
cellsize <- 1
cellcentre.offset <- bbox(points)[, 1]
coords.span <- diff(t(bbox(points)))
cells.dim <- ceiling(coords.span / cellsize)
grid <- SpatialGrid(GridTopology(cellcentre.offset, rep(cellsize,
nrow(bbox(points))), cells.dim))
in.cell <- overlay(grid, points)



PS R-sig-geo is a better list to ask spatial releated questions.

ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Reseach Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
tel. + 32 54/436 185
Thierry.Onkelinx op inbo.be

Do not put your faith in what statistics say until you have carefully
considered what they do not say.  ~William W. Watt
A statistical analysis, properly conducted, is a delicate dissection of
uncertainties, a surgery of suppositions. ~M.J.Moroney


> -----Oorspronkelijk bericht-----
> Van: r-help-bounces op stat.math.ethz.ch 
> [mailto:r-help-bounces op stat.math.ethz.ch] Namens Marco Visser
> Verzonden: woensdag 18 april 2007 20:57
> Aan: r-help op stat.math.ethz.ch
> Onderwerp: [R] Matrix or grid conversion of spatial data
> Dear Happy R-users & experts,
> I am in need of advice,
> While working with spatial data (x & y coordinates of seed 
> locations) I have come accross the problem that I need to 
> convert my point data into a matrix or grid system. I then 
> need to count how often a point falls into a certain position 
> in the matrix or grid. I have searched all day online, asked 
> collegeas but nothing works.
> Sadly my R "box of tricks" has run out.
> My (point) data looks like this;
> x         y
> 2.3    4.5
> 3.4      0.2
> and continues for another million records. 
> Now my question; is there any function that is able to 
> "count" how often a point falls into a grid based on the x 
> and y location? So I need to discretize the spatial locations 
> to a regular grid and then counting how often  a point occurs.
> Many thanks for your thoughts on this problem.
> Marco Visser
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