Good evening.
I just wanted to share the way I understand the project, so here's an email
I sent to Mr. Springmeyer. I'd appreciate any feedback you could give me:
Good evening Mr. Springmeyer, how are you?
I'm sending you this email to see if you could answer me some questions I
have about the 'Better Print Support' and to let you know about the picture
I have of it. Since you are visiting Mike Migurski and Tom Carden tomorrow,
it would be great if you could also share this email with them to make sure
that these ideas and questions make sense.
Talking to Waldemar and reading some resources in the OpenStreetMap wiki, I
found out that a major need this project has is the capability to customize
the way a map is printed in digital file formats, such as PDF, Illustrator's
and Inkcape's, so it can later be printed to paper of various sizes. People
find it hard to print a map correctly because difficult extra steps are
necessary, which require the knowledge of other tools, and the results are
sometimes inaccurate. To mention examples of the former issue, Nicolas
Marichal says that lacking the capability of turning on/off specific layers
the resulting map files tend to be too large to be handled properly
(Waldemar showed me a PDF file generated with MapOSMatic that was really
large and that caused his PDF viewer to crash (I hope this is what Nicolas
Marichal was talking about)), containing unnecessary elements the user may
not want to see in her map. About the latter issue, he mentions that some
elements are sometimes displayed in wrong positions ("water areas sometimes
appear wrong, as if the city is flooded"); I guess this is the result of
resizing or scaling the map.
To overcome these problems, you suggest that OSM's "Easy Printable Maps"
project should be based upon the work done in the "Better Print Support"
project, which will address some of the issues mentioned above. The
existence of tickets #343, #320, #389 and #358 is a sign that the intention
of improving Mapnik in these areas has existed for quite a long time now.
Reading the description of these tickets, I realize that they are indeed
related to what Graham Jones identifies as the main concerns of these two
projects, namely 'resolution', 'rendering options' and 'scale'. I'll comment
on these tickets next (please, tell me if any of the ideas I've mentioned so
far are wrong):
Ticket #343 (Add a resolution parameter to Map object): The goal here would
be to be possible for the user to specify the resolution at which the map
should be printed in the digital file (pdf, ai, inkscape, etc.), expressed
as a scaling factor that would manipulate the size of symbols, fonts, lines,
etc. The scaling should be done in such a way that the spatial relationships
between elements is preserved (to prevent lakes from moving, for example).
My question here would be if the capability of specifying a custom
resolution parameter is what you refer to as 'multi-resolution'.
Ticket #389 (Add optional but explicit units everywhere): As I understand,
Mapnik currently uses PPIs as the unit for specifying the resolution of the
map, but it is desirable that other measurement units, like mm, cm and
microns, be used as well (I'm not completely sure about this, though). As
the title of this ticket states, it should be possible to specify everything
that's measurable inside the map using various units (Robert Coup mentions
in his reply to my latest message in the mailing list that longitude and
latitude lines should also be displayed using units other than degrees, like
meters). Finally, the default unit should be pixels.
Ticket #320 (SVG-Based Symbolizers): I don't have enough information to
comment here, but Mr. Pavlenko said he is interested in an SVG renderer.
Ticket #358 (Implementation of map borders and coordinate grids similar to
those provided by GMT): The features discussed in this ticket are those that
Robert Coup suggested (in his reply to my message in the mailing list) and
that are already implemented in the experimental-pdf branch, but using
WXPDFDOC. The idea here is to provide these features with a Cairo-based
renderer.
My questions for Mr. Migurski and Mr. Carden would be:
#1 I don't fully understand what they mean with "use the same renderer for
web cartography as multi-resolution cartography". I interpret the sentence
as providing support for producing maps with different resolutions within
the same renderer (Cairo-based preferably).
#2 Does my vision of the project agree with theirs?
I'll post the contents of this email in the mailing list too. Maybe other
members might want to add their comments.
Thanks in advance.
Carlos Enrique López Garcés
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