R help - Feb 2004 - Readbin and file position

I have a binary file which is an image with multiple bands, arranged in BSQ
format such that R, B and G are all N x M sized matrices (corresponding to
Red, Blue and Green colors respectively).  The BSQ file arranges the data as
[R, B, G], so to access the B matrix, I have to read forward N x M + 1
number of samples.  Is there a fast way to define a variable as the B matrix
exclusively (e.g. Can I use readbin to "fast forward" N x M + 1
samples to
the beginning of the B matrix, and then read/define the B matrix
exclusively, or do I have to read the entire file into memory, then subset
out the B matrix?)

Thanks!

--j

-- 
Jonathan Greenberg
Graduate Group in Ecology, U.C. Davis
http://www.cstars.ucdavis.edu/~jongreen
http://www.cstars.ucdavis.edu
AIM: jgrn307 or jgrn3007
MSN: jgrn307 at msn.com or jgrn3007 at msn.com

Jonathan Greenberg wrote:
> I have a binary file which is an image with multiple bands, arranged in BSQ
> format such that R, B and G are all N x M sized matrices (corresponding to
> Red, Blue and Green colors respectively).  The BSQ file arranges the data
as
> [R, B, G], so to access the B matrix, I have to read forward N x M + 1
> number of samples.  Is there a fast way to define a variable as the B
matrix
> exclusively (e.g. Can I use readbin to "fast forward" N x M + 1
samples to
> the beginning of the B matrix, and then read/define the B matrix
> exclusively, or do I have to read the entire file into memory, then subset
> out the B matrix?)
> 
> Thanks!
> 
> --j
> 

?readBin points us to ?connections which finally points us to ?seek 
which is the function you are looking for.

Uwe ligges

The "seek" command will allow you to skip to a particular byte
position in
the file.  You can define the position you want relative to your current
position, or to the start of the file.

Hope this helps,

Matt Wiener

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Jonathan Greenberg
Sent: Thursday, February 12, 2004 9:51 PM
To: R-help
Subject: [R] Readbin and file position


I have a binary file which is an image with multiple bands, arranged in BSQ
format such that R, B and G are all N x M sized matrices (corresponding to
Red, Blue and Green colors respectively).  The BSQ file arranges the data as
[R, B, G], so to access the B matrix, I have to read forward N x M + 1
number of samples.  Is there a fast way to define a variable as the B matrix
exclusively (e.g. Can I use readbin to "fast forward" N x M + 1
samples to
the beginning of the B matrix, and then read/define the B matrix
exclusively, or do I have to read the entire file into memory, then subset
out the B matrix?)

Thanks!

--j

-- 
Jonathan Greenberg
Graduate Group in Ecology, U.C. Davis
http://www.cstars.ucdavis.edu/~jongreen
http://www.cstars.ucdavis.edu
AIM: jgrn307 or jgrn3007
MSN: jgrn307 at msn.com or jgrn3007 at msn.com

______________________________________________
R-help at stat.math.ethz.ch mailing list
https://www.stat.math.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html



------------------------------------------------------------------------------
Notice:  This e-mail message, together with any attachments,...{{dropped}}