mapnik python demo ol15

[darkblueb]

a mapnik python demo included in the dot-deb packaging fails [0]

earlier #osgeolive versions ref: ​https://trac.osgeo.org/osgeolive/ticket/2255

mapnik will render to a Jupyter Notebook:

​https://git.osgeo.org/gitea/darkblueb/ol14_ipynb_misc/src/branch/master/mapnik-py

TODO demo for ol15

==

mapnik

user@ol15nightly:~$ cp -R /usr/share/doc/python3-mapnik/examples/* mapnik_test/


user@ol15nightly:~/mapnik_test/demo/python$ python3 rundemo.py 
Traceback (most recent call last):
  File "/home/user/mapnik_test/demo/python/rundemo.py", line 322, in <module>
    mapnik.render(m, im)
RuntimeError: Cannot initialize proj_transform for given projections without proj4 support (-DMAPNIK_USE_PROJ4): '+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs'->'+proj=lcc +ellps=GRS80 +lat_0=49 +lon_0=-95 +lat+1=49 +lat_2=77 +datum=NAD83 +units=m +no_defs'

[kalxas]

Quickstart is also failing when using the MapProxy to render mapnik tiles.

[kalxas]

latest commits:

​https://github.com/mapnik/python-mapnik/commits/proj6

[darkblueb]

build 162 ol15

user@osgeolive:~/Downloads/python-mapnik-master/test$ ipython3
Python 3.10.4 (main, Apr  2 2022, 09:04:19) [GCC 11.2.0]
Type 'copyright', 'credits' or 'license' for more information
IPython 7.31.1 -- An enhanced Interactive Python. Type '?' for help.

In [1]: import mapnik

In [2]: m = mapnik.Map(512, 512)
   ...: 

In [3]: mapnik.load_map(m, 'data/good_maps/wgs842merc_reprojection.xml')
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-3-26cbb3ea7887> in <module>
----> 1 mapnik.load_map(m, 'data/good_maps/wgs842merc_reprojection.xml')

RuntimeError: Cannot initialize projection 'epsg:3857 ' without proj4 support (-DMAPNIK_USE_PROJ4) in Map at line 1 of 'data/good_maps/wgs842merc_reprojection.xml'

[sanak]

The error message itself seems to come from mapnik core library. ​https://github.com/mapnik/mapnik/blob/v3.1.x/src/proj_transform.cpp#L129-L134

#ifdef MAPNIK_USE_PROJ4
            source_.init_proj4();
            dest_.init_proj4();
#else
            throw std::runtime_error(std::string("Cannot initialize proj_transform for given projections without proj4 support (-DMAPNIK_USE_PROJ4): '") + source_.params() + "'->'" + dest_.params() + "'");
#endif

I compared libmapnik between OSGeoLive 14.0 and 15.0beta1 environments, and I noticed that OSGeoLive 15.0beta1 libmapnik3.1 seems not to link to libproj.

• OSGeoLive 14.0

  $ dpkg -l | grep libmapnik
  ii  libmapnik3.0 ...
  :
  $ dpkg -L libmapnik3.0
  :
  /usr/lib/libmapnik.so.3.0
  $ ldd /usr/lib/libmapnik.so.3.0 | grep libproj
          libproj.so.19 ...
  

• OSGeoLive 15.0beta1

  $ dpkg -l | grep libmapnik
  ii  libmapnik3.1 ...
  :
  $ dpkg -L libmapnik3.1
  :
  /usr/lib/libmapnik.so.3.1
  $ ldd /usr/lib/libmapnik.so.3.1 | grep libproj
  

So, I guess that rebuilding libmapnik3.1 with -DMAPNIK_USE_PROJ4 flag or downgrading to libmapnik3.0 may solve this issue.

[Bas Couwenberg]

Mapnik 3.x doesn't support proj.h: ​https://github.com/mapnik/mapnik/issues/4036

I cannot be bothered to backport the changes ​like Fedora did, see:

• ​https://bugs.debian.org/997049
• ​https://bugs.debian.org/1009028

[sanak]

Replying to Bas Couwenberg:

Mapnik 3.x doesn't support proj.h: ​https://github.com/mapnik/mapnik/issues/4036

I cannot be bothered to backport the changes ​like Fedora did, see:

• ​https://bugs.debian.org/997049
• ​https://bugs.debian.org/1009028

Okay, thanks for the information.

From the Fedora person (Tom Hughes)'s patch's comment link (​https://github.com/mapnik/mapnik/pull/4202) and his (@tomhughes) fork ​fedora branch's history, applying the following commit may be enough, but I don't know well about Debian packaging things...

• ​https://github.com/tomhughes/mapnik/commit/8944e81367d2b3b91a41e24116e1813c01491e5d

OSGeoLive 15 rc1 documentation freeze for the english version is planned at tomorrow (or a day after tomorrow), so I think that there is no enough time to search alternative way instead of using mapnik.

[darkblueb]

I have the Mapnik core cloned here, and can manually apply that patch to the code. What happens after that?

Mapnik loads a dozen major graphics libraries. The build is not easy, but it is possible. For language bindings, I can load, test and understand the results of python, but probably not NPM or the others so quickly.

[kalxas]

Thanks all for the feedback.

mapnik package now patched with the commit:

​https://github.com/tomhughes/mapnik/commit/8944e81367d2b3b91a41e24116e1813c01491e5d

​https://launchpad.net/~gcpp-kalxas/+archive/ubuntu/osgeolive/+sourcepub/13844321/+listing-archive-extra

[sanak]

Replying to kalxas:

Great!
Thanks for the update!

[kalxas]

python3-mapnik patched from proj6 upstream branch:

​https://launchpad.net/~gcpp-kalxas/+archive/ubuntu/osgeolive/+sourcepub/13844380/+listing-archive-extra

[kalxas]

After installing the new packages on top of build163, the test code seems to work now (see screenshot) but the mapproxy demo still fails. Perhaps a configuration issue?

[darkblueb]

confirm build 167-staging

user@osgeolive:~$ ldd /usr/lib/libmapnik.so.3.1.0 | grep proj
        libproj.so.22 => /lib/x86_64-linux-gnu/libproj.so.22 (0x00007f7cf20b4000)

[sanak]

Okay, thanks for the information.
I also confirmed it.

user@osgeolive:~$ ldd /usr/lib/libmapnik.so.3.1.0 | grep proj
        libproj.so.22 => /lib/x86_64-linux-gnu/libproj.so.22 (0x00007f1252217000)

---

but the mapproxy demo still fails. Perhaps a configuration issue?

About this mapproxy demo failing, the error message was changed to failed to initialize projection with: '+init=epsg:3857', and from googling a bit, the cause seems to be in mapproxy side.

• ​https://github.com/mapproxy/mapproxy/issues/538
• ​https://github.com/mapproxy/mapproxy/issues/136#issuecomment-42392618

From above 2nd link, I patched /usr/lib/python3/dist-packages/mapproxy/source/mapnik.py as follows locally, then I could show the mapnik layer correctly.

-         m.srs = '+init=%s' % str(query.srs.srs_code.lower())
+         m.srs = str(query.srs.srs_code.lower())

[sanak]

About above patching location, I guess that patching python3-mapproxy itself may be better than patching it on OSGeoLive bin/install_mapproxy.sh.

[darkblueb]

​https://github.com/OSGeo/OSGeoLive/pull/347

[kalxas]

Thanks all for the feedback!

I have now ported mapproxy 1.15.1 from debian and patched the package itself. We will know the result in a while.

[kalxas]

The mapproxy mapnik demo now works!

I will build a new iso and close this after we confirm.

[kalxas]

Confirmed fixed in build178