Roger,

Thanks for your help.  I believe you are correct that the printed summary 
values have been rounded.  I couldn't quite figure out how to extract the 
range specifically, but when I did a summary for the data.frame from each 
grid I got what I was expecting for the one created by readAsciiGrid (g1). 
 However, the grid created by readGDAL (g2) still shows unexpected min and 
max values.  See results below:

> d1 <- g1@data
> summary(d1)
 distrail_100m.asc
 Min.   :      0 
 1st Qu.:   2878 
 Median :   6562 
 Mean   :   7896 
 3rd Qu.:  11670 
 Max.   :  37082 
 NA's   :6483714 

> d2 <- g2@data
> summary(d2)
     band1 
 Min.   : -32768 
 1st Qu.:   2844 
 Median :   6516 
 Mean   :   7718 
 3rd Qu.:  11600 
 Max.   :  32767 
 NA's   :6483714 

For my own purposes, I have found that I should continue using 
readAsciiGrid to bring in my grids.  But I would be happy to share my 
dataset to help figure out why readGDAL has these strange results.  My 
Ascii file is 13Mb zipped, probably too large to email, and I don't have 
an FTP site that can be accessed outside of the Forest Service.  I can 
send the file to you off list using YouSendIt.com if you would like, or if 
you have an alternative suggestion for transferring the file, let me know. 
 Thanks again for your assistance, and if you need any additional 
information from me, let me know.

Cheers,
-Brian

=======================
Brian R. Miranda
USDA Forest Service
Northern Research Station
brmiranda@fs.fed.us

Institute for Applied Ecosystem Studies
5985 Highway K
Rhinelander, WI  54501
phone: 715-362-1186
fax: 715-362-1166





Roger Bivand <Roger.Bivand@nhh.no> 
01/13/2009 02:49 PM
Please respond to
Roger.Bivand@nhh.no


To
Brian R Miranda <brmiranda@fs.fed.us>
cc
r-sig-geo@stat.math.ethz.ch
Subject
Re: [R-sig-Geo] ESRI Ascii Grid






On Tue, 13 Jan 2009, Brian R Miranda wrote:

> Hello,
>
> I have an Ascii grid that was created using the GridAscii command in
> ArcGrid.  The grid represents cell distance to railroads and has values
> ranging from 0 to 37,082.  When I bring this grid into R as a
> SpatialGridDataFrame, the maximum and/or the minimum values in the grid 
do
> not exactly match the original grid.  I have tried using both readGDAL 
and
> readAsciiGrid for this purpose.  I have confirmed in a text editor that
> the Ascii file does contain the maximum value of 37,082.  Below are the
> results I have seen.  Note the differences in the Max. value and Min.
> value (from readGDAL).

First, beware of the possible difference between the printed summary value 

and the actual value - printed summaries may round. What does range() of 
the variable say? The difference between the two functions is puzzling - 
could you make the data available (off list for example, zipped, 
preferably for download) to try to see what is going on?

Roger

>
>> g1 <- readAsciiGrid("G:/Oconto/WI_Fire/distrail_100m.asc")
>> summary(g1)
> Object of class SpatialGridDataFrame
> Coordinates:
>                min      max
> coords.x1 -263487.6 149512.4
> coords.x2  358821.1 666821.1
> Is projected: NA
> proj4string : [NA]
> Number of points: 2
> Grid attributes:
>  cellcentre.offset cellsize cells.dim
> 1         -263437.6      100      4130
> 2          358871.1      100      3080
> Data attributes:
>   Min. 1st Qu.  Median    Mean 3rd Qu.    Max.    NA's
>      0    2878    6562    7896   11670   37080 6483714
>
>> g2 <- readGDAL("G:/Oconto/WI_Fire/distrail_100m.asc")
> G:/Oconto/WI_Fire/distrail_100m.asc has GDAL driver AAIGrid
> and has 3080 rows and 4130 columns
>> summary(g2)
> Object of class SpatialGridDataFrame
> Coordinates:
>        min      max
> x -263487.6 149512.4
> y  358821.1 666821.1
> Is projected: NA
> proj4string : [NA]
> Number of points: 2
> Grid attributes:
>  cellcentre.offset cellsize cells.dim
> x         -263437.6      100      4130
> y          358871.1      100      3080
> Data attributes:
>   Min. 1st Qu.  Median    Mean 3rd Qu.    Max.    NA's
> -32770    2844    6516    7718   11600   32770 6483714
>
> The results from readAsciiGrid are pretty close (Max = 37,080) to the
> original grid, but readGDAL results in much different values.  I would
> expect both functions to create an object with exactly the same values 
as
> the Ascii grid.  Can anyone explain why this occurs, and if there is a
> different way to get my grid into R (I eventually need an 'im' to work
> with)?  I am new to spatial analysis using R, so if there is something
> obvious I am missing I apologize.  Thanks in advance for any help!
>
> Cheers,
> -Brian
>
>
> =======================
> Brian R. Miranda
> USDA Forest Service
> Northern Research Station
> brmiranda@fs.fed.us
>
> Institute for Applied Ecosystem Studies
> 5985 Highway K
> Rhinelander, WI  54501
> phone: 715-362-1186
> fax: 715-362-1166
>
>
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>
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> R-sig-Geo mailing list
> R-sig-Geo@stat.math.ethz.ch
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>

-- 
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@nhh.no



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