[mapguide-users] MrSID files through GDAL FDO provider

[Kenneth, GEOGRAF A/S]

I looked at the way the providers are registered and tested in the GDAL 
library.
I think it would be a relatively small addition, to be able to provide 
"hints" to the driver.

The current problem is the Open() call, which tests the providers in turn.
If there was a file in the folder (say "GDAL Loader Hints.txt" stating ea.:
MrSID
ECW

The provider could try these first. It is of course also an overhead, 
but testing for a file's existence should be
a relatively low cost operation. Actually reading and parsing the files 
should be faster than the current
probing. I would recommend that this would be a hint only, and that the 
library should try all providers,
if none of the hinted providers succeed.

Regards, Kenneth, GEOGRAF A/S



Frank Warmerdam skrev:
> Martin Morrison wrote:
>> If the mapguide tries each provider in order to open an image, how much
>> performance gain is there by only using one raster format and compiling
>> only that driver?  Or can you specify the order in which the drivers are
>> polled?
>
> Martin,
>
> There would be no appreciable improvement in performance - at least
> for files that actually open.  The case that the "test each in sequence"
> thing tends to get inefficient is for files that fail to open because 
> then
> all the drivers are tested.  And there are sometimes a few drivers at the
> bottom of the list that are somewhat expensive.  For instance, probing 
> for
> header files and such.
>
> It is possible to only register required drivers but I think this is a
> relatively pointless optimization in the grand scheme of things.
>
> Best regards,