[Qgis-user] Unable to open MrSID file in QGIS even if gdalinfo can read it

[Even Rouault]

Le 04/10/2024 à 18:06, Andrew Plowright a écrit :
> Thanks again Even and Fernando, you've both provided a lot of helpful 
> information that has turned this into a very instructive Linux 
> learning opportunity.
>
> Even: can I confirm that, in the third option you suggested (the "less 
> ugly alternative"), this would involve:
>
> 1. Installing QGIS using Software Manager (or any other way, just not 
> necessarily building it from source)
> 2. Building a second instance of GDAL from source which has the same 
> version as whatevever GDAL version is created by the QGIS installation 
> (ex.: 3.8.4) and which is built with the Mr Sid driver.
> 3. This second instance of GDAL is given its own secluded 
> /opt/gdal_3_8_4 folder to keep it separate from /usr
> 4. Setting GDAL_DRIVER_PATH will make GDAL search 
> /opt/gdal_3_8_4/lib/gdalplugins for additional plugins, such as the 
> MrSid driver. This should affect any instance of GDAL, whether I'm 
> running it through QGIS or through the command line?
>
> Did I get all that correct?
yes
>
> On Sat, Sep 28, 2024 at 10:33 AM Even Rouault 
> <even.rouault at spatialys.com> wrote:
>
>     Andrew,
>
>
>>     $ ldd /bin/qgis.bin | grep gdal
>>
>>     libgdal.so.34 => /lib/x86_64-linux-gnu/libgdal.so.34
>>     (0x00007a0581a00000)
>>
>>     But I'm not sure what to do with that information.
>
>     /lib/x86_64-linux-gnu/libgdal.so.34 is the version of GDAL that
>     comes with package manager, so 3.8.4 here
>
>     I'm not sure how you are familiar with the dynamic linking
>     concepts and tools, but if you're not, reading
>     https://opensource.com/article/22/5/dynamic-linking-modular-libraries-linux
>     or related resources on dynamic linking might help you understand
>     why those seemlingly "weird" behaviors are totally explainable.
>     Takes time, and even with experience, mixing up several versions
>     of a library on a system and being confused is not uncommon
>
>     I'm going to hate myself for the below suggestion, and you
>     probably too when it will hit you back in the face (so forget I've
>     told you about it ;-),  ... but ... to quickly workaround your
>     issue, you can do:
>
>     sudo ln -s /usr/lib/libgdal.so.35 /usr/lib/libgdal.so.34       #
>     i'm already hating myself
>
>     sudo mv /lib/x86_64-linux-gnu/libgdal.so.34
>     /lib/x86_64-linux-gnu/libgdal.so.34.disabled    # I'm hating
>     myself even more...
>
>     And now launch QGIS.... As GDAL keeps a backwards compatible C
>     ABI, this ugly substitution of the expected GDAL 3.8.4 version at
>     build time is supposed to (mostly) work. That said, you might run
>     in occasional bugs, where QGIS tries to workaround GDAL specific
>     bug, based on the version of GDAL QGIS was built against...
>
>     OK, I believe you've been sufficienly warned this is *not* the
>     normal way of proceeding, just a quick&dirty workaround
>
>     To undo the above mess:
>
>     sudo mv /lib/x86_64-linux-gnu/libgdal.so.34.disabled
>     /lib/x86_64-linux-gnu/libgdal.so.34
>
>     sudo mv /usr/lib/libgdal.so.34 /usr/lib/libgdal.so.34.disabled 
>     (i'm always nervous doing a rm in /usr territory, so I tend to
>     just rename ...)
>
>     The clean solution would be that you rebuild QGIS against your
>     installed GDAL, but that would be for another episode. Another
>     friendly advice would be that when doing a custom build you don't
>     do CMAKE_INSTALL_PREFIX=/opt , but here something like
>     CMAKE_INSTALL_PREFIX=/opt/gdal_3_10_master to avoid messing with
>     /usr which should be only the territory of your package manager tool.
>
>
>     Another less ugly alternative would be that you download
>     http://download.osgeo.org/gdal/3.8.4/gdal-3.8.4.tar.gz, build it
>     with support of the MrSID driver as a plugin, with
>     -DGDAL_ENABLE_DRIVER_MRSID_PLUGIN=ON, install it in
>     /opt/gdal_3_8_4, and then just set the
>     GDAL_DRIVER_PATH=/opt/gdal_3_8_4/lib/gdalplugins environment
>     variable. That way you would use the system GDAL library with just
>     the addition of the MrSID driver.
>
>     Actually that might not be terribly harder to do than my above
>     hacks, so I'm definitely encouraging you to explore that way
>
>     And ... you should know that the company behind the MrSID SDK has
>     declared they won't ever release any new binary version of it.
>     This means that at most in a few years, this SDK will likely be
>     totally unusable on modern systems. So everyone using SID files
>     had better convert them to something else, like COG, when they
>     still have a chance...
>
>     /me taking a passport to an undisclosed country without
>     extradition agreement.
>
>     Even
>
>     -- 
>     http://www.spatialys.com
>     My software is free, but my time generally not.
>
-- 
http://www.spatialys.com
My software is free, but my time generally not.
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