[Gdal-dev] Enhancement to access Arc/Info Binrary Grid in zip file

[Kevin Ruland]

Frank,

Thanks much for the sanity check.  Random access writes would hurt.  
About the only way for it to work effectively would be to unzip into 
memory, modify, and rezip.

I was digging through the aigrid code and see that it manipulates file 
pointers directly, so it would be a great effort to work it in even for 
my prinicipal interest,  read-only access.

Kevin

Frank Warmerdam wrote:

> Kevin Ruland wrote:
>
>> I've been lurking for a little while and am a relatively new user of 
>> the GDAL library.  Please excuse any "neubies" I might make.
>>
>> I'm in the process of cataloging all of our raster datasets and am 
>> troubled by the Arc/Info multiple file setup.  Keeping track of 
>> multiple files is significantly harder than tracking them all in, 
>> say, a zip file.  I was wondering if anyone has considered storing 
>> these multi-resource formats in a container of some kind, what the 
>> implications are, and if it would even be worthwile to persue.
>
>
>
> Kevin,
>
> I don't think it would be particularly easy to implement this though 
> it is in theory doable, at
> least for one format at a time.
>
> One problem is that formats like Arc/Info binary coverages are random 
> access, and in a zip
> file each file is compressed as one big stream.  That means if you 
> want data from the middle
> of the file, you need to uncompress all the preceeding data (and 
> discard it) to get the data
> you want.  In some cases this could completely hammer performance.
>
> While I sympathaize with your concern about managability of directory 
> trees, I am doubtful
> it is practical from a work or a performance point of view to change 
> most of the multi-file
> formats to support zipped version.
>
> Best regards.
>