I believe I've got Mapnik reading the DNC data now. Everything seemed to
work except that the file existence check in ogr_datasource.cpp isn't
formulated to accept the OGDI driver's file string format
(gltp://<driver>/<file>). I simply commented out the check at line 71
if (!boost::filesystem::exists(dataset_name_))...
and rebuilt the plugin. The data loaded (and subesquently seemed to plot)
fine with
lyr.datasource =
mapnik.Ogr(file='gltp:/vrf/home/<user>/dnc/dnc13/a1316120',
layer='coa...@ecr(*)_line')
A more robust modification shouldn't be too difficult.
As Jeff mentioned, we've also been discussing importing the data into a
postgis database using ogr2ogr and I have been pursuing that route as well.
I am admittedly very new at this, but that would seem to offer some
advantages. I would appreciate any feedback on the potential pros and cons
of the postgis vs the direct approach.
Thank again,
-- Ryan
On Thu, May 7, 2009 at 1:29 PM, Ryan Halterman <[email protected]> wrote:
> Thanks for the reply Dane,
>
> On Thu, May 7, 2009 at 12:07 PM, Dane Springmeyer <[email protected]>wrote:
>
>> Hey Ryan,
>>
>>
>> On May 6, 2009, at 5:22 PM, Ryan Halterman wrote:
>>
>> Hello,
>>>
>>> I am trying to read NGA Digital Nautical Charts (VPF/VRF format) into
>>> Mapnik. To do so, I am attempting to create a datasource using the OGDI
>>> driver through the ogr plugin. I have built Mapnik in Ubuntu 8.10 (and
>>> 9.04) with debug on and with ogr support. Upon importing Mapnik, I receive
>>> confirmation of the ogr plugin's existence. I am able to run ogrinfo on the
>>> DNC data source and receive a list of layers using the following command:
>>>
>>> ogrinfo gltp:/vrf/home/<user>/dnc/dnc13/a1316120
>>>
>>
>> Fascinating - i've never heard of this file format.
>>
>>
>>>
>>> One of the layers listed is:
>>>
>>> 11: coa...@ecr(*)_line (Line String)
>>>
>>> In order to create the data source in Mapnik, I am attempting the
>>> following:
>>>
>>> lyr = mapnik.Layer('test', "+proj=latlong +datum=WGS84")
>>> lyr.datasource = mapnik.Ogr(file='/home/<user>/dnc/dnc13/a1316120',
>>> layer='coa...@ecr(*)_line')
>>>
>>> This gives a runtime error indicating line 299 in mapnik/__init__.py
>>> (return CreateDatasource(keywords))
>>>
>>>
>>
>> What is the full error?
>
>
> There is no error message when calling through mapnik.Org(), simply a blank
> runtime error. It did show that the error occurred at line 299 of
> __init__.py. That is what led me to call it through CreateDatasource().
>
>
>>
>>
>>
>> Maybe try:
>>
>> lyr.datasource =
>> mapnik.Ogr(file='gltp:/vrf/home/<user>/dnc/dnc13/a1316120',
>> layer='coa...@ecr(*)_line')
>>
>
> I tried that initially as well, but that returned a "File not found" error.
>
>
>>
>>
>> Without being at all certain of its correctness, I also attempted to call
>>> CreateDatasource directly with the following:
>>>
>>>
>> This will be no different that calling the Ogr function, which just wraps
>> CreateDatasource.
>>
>
> The only difference is that the python shell (iPython) actually returns an
> error message (as seen below) when called with CreateDatasource().
>
>
>>
>>
>> lyr.datasource = mapnik.CreateDatasource(type='ogr',
>>> file=/home/<user>/dnc/dnc13/a1316120', layer='coa...@ecr(*)_line')
>>>
>>>
>> Looks like you are missing a single quote after 'file'
>>
>
> Sorry. That was there when I issued the command. It just didn't make it
> into my post.
>
>
>>
>> This returns the following:
>>> ArgumentError: Python argument types in
>>> mapnik._mapnik.CreateDatasource() did not match C++ signature:
>>> CreateDatasource(boost::python::dict)
>>>
>>> I am able to use ogr2ogr to convert the DNC to a shapefile and then
>>> import that into Mapnik, but I would greatly prefer to not have to go
>>> through that step. Any suggestions or insight anyone may have about this or
>>> reading Digital Nautical Charts in general would be appreciated.
>>>
>>
> Thanks again for your time. Any further comments are appreciated.
>
> -- Ryan
>
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