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

[Aubrey Moore]

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