[R-sig-Geo] Plotting satellite image in R via sp package -> grid

[Roger Bivand]

On Wed, 30 May 2007 Jan.Verbesselt at csiro.au wrote:

> Dear,
> 
> I would like to plot an grid (subset of a satellite image in Sinusoidal
> projection) as an spatialobject in R via the sp package (R version 2.5,
> winXP).
>  
> The following works fine:
> sinusgrid <- read.table( see for data sample below , header=TRUE,
> sep=",", 	na.strings="NA", dec=".", strip.white=TRUE)
> sinusgrid <- as.data.frame(sinusgrid)
> coordinates(sinusgrid)=~x+y
> proj4string(sinusgrid) = CRS("+proj=sinu +lon_0=0 +x_0=0 +y_0=0
> +a=6371000 +b=6371000 +units=m")  # Sinusoidal projection
> 	
> l2 = list("SpatialPolygonsRescale", layout.north.arrow(), offset =
> c(13416000,-3939000), scale = 500)
> l3 = list("SpatialPolygonsRescale", layout.scale.bar(), offset =
> c(13416000,-3940000), scale = 1000, fill=c("transparent","black"))
>         spplot(sinusgrid, "ndvi", do.log = TRUE,
> key.space=list(x=0.2,y=0.8,corner=c(0,1)), scales=list(draw=T), cuts =
> 4,
>      sp.layout=list(l2,l3) )
> 
> But when I try ;
> gridded(sinusgrid) <- TRUE
> 
> I obtain the following error message:
> suggested tolerance minimum: 4.31585196603024e-06Error in
> points2grid(points, tolerance) : dimension 1 : coordinate intervals are
> not constant
> 
> before I can use image(sinusgrid) in order to create a spatial map to
> which I could overlay vectorlayers and points.
> 
> The data is extracted from a satellite image which was projected in
> sinusoidal projection (ProjParams =
> (6371007.181000,0,0,0,0,0,0,0,21600,0,1,0,0).
> 
> How could this satellite data be projected in R such that other shape
> files and points can be overlaid on the map?

As a guess, the ASCII coordinates are losing digits somewhere, so I'd take 
cbind() of the data frame coordinate columns and use SpatialPixels() 
directly, setting the tolerance= argument to a value that works for you. 
Then add back the index column as a data frame in the data= argument to 
SpatialPixelsDataFrame(). The gridded<- method doesn't let you set the 
tolerance, so go round by the side door.

Hope this helps,

Roger

> 
> Regards and thx,
> Jan
> 
> 
> ### Data set: pixels of an satellite image.
> x,y,index
> 13415234.67,-3935966.551,0.83
> 13415234.67,-3936198.255,0.83
> 13415234.67,-3936429.96,0.82
> 13415234.67,-3936661.665,0.87
> 13415234.67,-3936893.369,0.87
> 13415234.67,-3937125.074,0.87
> 13415234.67,-3937356.779,0.88
> 13415234.67,-3937588.483,0.86
> 13415234.67,-3937820.188,0.88
> 13415234.67,-3938051.893,0.77
> 13415234.67,-3938283.597,0.77
> 13415234.67,-3938515.302,0.92
> 13415234.67,-3938747.006,0.89
> 13415234.67,-3938978.711,0.89
> 13415234.67,-3939210.416,0.81
> 13415234.67,-3939442.12,0.76
> 13415234.67,-3939673.825,0.76
> 13415234.67,-3939905.53,0.85
> 13415234.67,-3940137.234,0.85
> 13415466.38,-3935966.551,0.83
> 13415466.38,-3936198.255,0.82
> 13415466.38,-3936429.96,0.83
> 13415466.38,-3936661.665,0.83
> 13415466.38,-3936893.369,0.87
> 13415466.38,-3937125.074,0.89
> 13415466.38,-3937356.779,0.80
> 13415466.38,-3937588.483,0.86
> 13415466.38,-3937820.188,0.88
> 13415466.38,-3938051.893,0.87
> 
> 
> ______________________________________________
> Jan Verbesselt, Phd
> Post-Doctoral Research Fellow - Remote sensing
> Ensis - the joint forces of CSIRO and Scion
> Private Bag 10
> Clayton South, VIC 3169, Australia
> Tel: + 61 3 9545 2265 
> Fax: + 61 3 9545 2448
> 
> _______________________________________________
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> R-sig-Geo at stat.math.ethz.ch
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> 

-- 
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.Bivand at nhh.no