R - raster function NAs values lower than -9999 in ASCII file

Question

I have been having problems importing a ASCII raster that has values that go from Min. :-69826220 Min. :-69826220 to Max. :167780500 Max. :167780500 . The problem I am encountering is that when I use the raster function to import the ASCII file then every value smaller than -9999 is reported as NA and the minimum value is -9458 .

Is this a bug of the function and is there a workaround? When I import the same ASCII file as a data frame everything is fine and I get the whole range of values. Also I am using the same procedure to import other ASCII rasters and don't have any problem.

here is the link to the ASCII file https://dl.dropboxusercontent.com/u/24234831/ps0011yme.asc

Here is the session info, I opened a new session just in case.

sessionInfo() R version 3.0.0 (2013-04-03) Platform: x86_64-w64-mingw32/x64 (64-bit)

locale: [1] LC_COLLATE=English_United States.1252 [2] LC_CTYPE=English_United States.1252
[3] LC_MONETARY=English_United States.1252 [4] LC_NUMERIC=C
[5] LC_TIME=English_United States.1252

attached base packages: [1] stats graphics grDevices utils datasets methods base

other attached packages: [1] raster_2.1-16 sp_1.0-8

loaded via a namespace (and not attached): [1] grid_3.0.0 lattice_0.20-15

Any help is appreciated

Answer 1

You can try to use setMinMax() on your raster file to try and work out the min and max values and store them in the returned Raster* object. Try it like so:

r <- setMinMax( raster("path/to/myraster.asc") )

I am not sure what is happening because if I downlaod you data and do:

r1 <- raster( "~/Downloads/test.asc")
summary(values(r1))
     Min.   1st Qu.    Median      Mean   3rd Qu.      Max.      NA's 
-69830000  -4789000    737300  16950000  13880000 167800000     71468

Please add the output of sessionInfo() into your question , ie not as a comment.

The errors in this case were being caused by not having rgdal installed, which are bindings to the Geospatial Data Abstraction Library and are very important for importing/exporting raster and shapefile data.

Answer 2

I'm unable to reproduce your error. Here's a hand-built .asc file:

NCOLS 3 
NROWS 3 
XLLCORNER 0 
YLLCORNER 0 
CELLSIZE 0.5 
NODATA_value -9999 
1e-6 0.3 -34567891234
0.2 -1e6 25
3 68492758321934 20

That loaded correctly into a raster object. You'll notice the NODATA_value item there, which explains where your -9999 come from. My bet is that there's something corrupted in your source .asc file. Can you post the header and a small sample of the data?

Answer 3

The internal ascii file driver in 'raster' assumes that there are no valid values lower than the NA flag value if the flag value is < 0 (and I would not recommend using an NA flag in the middle of the values). Clearly, this approach can cause problems like in this case; and I will change that. You can see the difference between the internal driver and the gdal driver if you do

 library(raster)
 library(rgdal)
 a1 <- raster(filename, native=TRUE)
 a2 <- raster(filename, native=FALSE)