On Wed, Oct 3, 2012 at 9:20 PM, <jin...@ga.gov.au> wrote:
> ** ** ** ** ** **
>
> Hi Robert,****
>
> Thank you very much for the reply. Both datasets are in txt format. Lat
> and long are in WGS84. So I might need to do something like:****
>
> library(raster)****
>
> p <- read.table('points.txt')****
>
> d <- read.table('gridcells.txt')****
>
> r <- rasterFromPoints(d)****
>
> values<- extract(r, p)****
>
> ** **
>
> Is anything else I should add or modify? rasterFromPoints seems not
> available in raster 2.0-05.
>
Sorry, I misspoke, I should have said "rasterFromXYZ"
I still do not know what "d" looks like. "txt format" is not very
descriptive, but if it regular spaced points, something like
x, y, z
1, 2, 3,
1, 3, 5
then you can probably do what you write above, using rasterFromXYZ instead
of rasterFromPoints
Robert
****
>
> ** **
>
> What I intend to do is extract and add lat/long of corresponding grid
> cells to my points dataset as below:****
>
> > points****
>
> lat.sample long.sample lat.gridcell long.gridcell ****
>
> 1 -21.258000 110.502000****
>
> 2 -42.609683 144.412700****
>
> 3 -36.733000 132.050000****
>
> 4 -21.330000 110.482000****
>
> 5 -13.156840 136.757080****
>
> 6 -14.633000 117.967000****
>
> 7 -23.502580 111.083450****
>
> 8 -15.674870 138.058400****
>
> 9 -12.650000 136.950000****
>
> 10 -9.955000 143.806667****
>
> ** **
>
> All the best,****
>
> Jin****
> ------------------------------
>
> *From:* Robert J. Hijmans [mailto:r.hijm...@gmail.com]
> *Sent:* Thursday, 4 October 2012 1:13 PM
> *To:* **Li Jin**
> *Cc:* **r-sig-geo@r-project.org**
> *Subject:* Re: [R-sig-Geo] Extract location information from grid cells
> for sample points [SEC=UNCLASSIFIED]****
>
> ** **
>
> Hi Jin, ****
>
> ** **
>
> From your description it is not entirely clear what your input data looks
> like. But you can something like this****
>
> ** **
>
> library(raster)****
>
> p <- read.table('points.txt')****
>
> r <- raster('file.asc')****
>
> values<- extract(r, p)****
>
> ** **
>
> Perhaps you need to subset "p" to get the appropriate columns representing
> longitude and latitude (in that order). Or perhaps your grid data is not
> really in a 'raster' format? I am not sure from your description. In that
> case you may need to to****
>
> ** **
>
> d <- read.table('file.asc')****
>
> r <- rasterFromPoints(d)****
>
> ** **
>
> You may also want to check out functions cellFromXY to link coordinates to
> cells in a raster.****
>
> ** **
>
> All the best, Robert****
>
> ** **
>
> On Wed, Oct 3, 2012 at 5:38 PM, <jin...@ga.gov.au> wrote:****
>
> Dear list,
>
> I have two datasets: one is for point samples with lat and long
> information at accuracy of 0.001 degrees. Another is grid cells at a
> resolution of 0.0025 degrees. Both datasets are in txt format. Now I need
> to extract the lat and long information from the grid cell dataset for the
> point samples by assigning the lat and long of a grid cell to a sample
> point that falls in the grid cell. I usually get this done in ArcGIS. I was
> wondering if it is possible in R. I searched but failed to find a right
> function to implement this in R.
>
> Many thanks for any suggestions.
>
> Regards,
>
> Jin Li
> Spatial Modeller/Computational Statistician | Coastal, Marine and
> Climate Change Group
> Environmental Geoscience Division | GEOSCIENCE ****AUSTRALIA****
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