[R-sig-Geo] How to handle large negative numbers in GeoTIFF DEM?

[Michael Sumner]

x$band1[x$band1 <=-3.403e+38] <- NA

Use 0 instead of NA if you like, but zero might be a valid value in your 
case. You may need to be more flexible with the value used for 
comparing, so something like this should be safe

x$band1[x$band1 <= (-3.403e+37)] <- NA

HTH, Mike

Aubrey Moore wrote:
> Hi All,
>
> I am trying to display a DEM for the island of Guam.  The data were 
> downloaded in GeoTIFF format from the National Elevation Dataset 
> (http://ned.usgs.gov/).  It appears that some rectangular areas of the 
> ocean in this DEM been assigned an elevation attribute of -3.4E38 (see 
> output below).  How can I change these values to something more 
> realistic, like zero, before displaying the image? 
>
> - Aubrey
> ___________________________________________
>
>  > x=readGDAL(file.choose())
> C:\Documents and Settings\Owner\My 
> Documents\GuamDEM\NED_66800217\NED_66800217.tif has GDAL driver GTiff
> and has 1612 rows and 1365 columns
> Closing GDAL dataset handle 0x00236838...  destroyed ... done.
>  > summary(x)
> Object of class SpatialGridDataFrame
> Coordinates:
>         min       max
> x 144.58611 144.96528
> y  13.22667  13.67444
> Is projected: FALSE
> proj4string :
> [+proj=longlat +ellps=GRS80 +datum=NAD83 +no_defs +towgs84=0,0,0]
> Number of points: 2
> Grid attributes:
>   cellcentre.offset     cellsize cells.dim
> x         144.58625 0.0002777778      1365
> y          13.22681 0.0002777778      1612
> Data attributes:
>      band1           
>  Min.   :-3.403e+38  
>  1st Qu.:-3.403e+38  
>  Median : 0.000e+00  
>  Mean   :-1.224e+38  
>  3rd Qu.: 7.907e+00  
>  Max.   : 4.029e+02
>
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