Hello!
I'm a physics student applying for this year's summer of code. I've
written a proposal and would like to get comments from the community. I've
attached the proposal to this email. Please comment on it to, so I know if
it is good or what could be changed.
Thanks everybody for your help!
Regards,
Hermann Kraus
Short description
-----------------
The goal of this project is to implement functionality to output metadata
to make certain things on the map clickable. I'll add tools to make the
common use cases very easy for the user.
Rationale
---------
Having maps with clickable objects makes it easier for the user to obtain
information about objects on the map. Since a few month Google Maps
enables you to click on a restaurant, tourist attraction, etc. icon on the
map and more data is displayed. Currently maps created with Mapnik can't
easily do this, because Mapnik only outputs the bitmap data but no
information about where features have been placed. If one tries to do it
one has to project the clickable features by another program. This is
unnecessary work and not always possible. For example when there is no
icon but a text label it will be very hard to determine the actual size of
the label.
I expect this to get worse in the future when Mapnik's placement
algorithms get more intelligent. For example it might decide to move a
road a few pixel to make place for another road, combine multiple icons
into one, …
Motivation
----------
I really like Mapnik's clean rendering style and would like to make it
even more useful by enabling users to click on features, no matter where
Mapnik decided to place them. For example OpenStreetMap would profit much
from this change, as there is a lot of information in the database which
is not rendered at the moment. It could be made available by clicking on
objects (just like Google does now). Currently it would be quite complex
to do this because a second projection pass by different software would be
required and it might break with future improvements in Mapnik (as
described above). It also could happen that some features are suppressed
during rendering which would still be clickable and therefore confuse the
user.
Why did I choose this project: Looking for a project I also checked
Mapnik's open trac tickets and but most things there looked like they
wouldn't be suited for a summer of code project. I think this project will
really help a lot of users and perhaps some new users will discover Mapnik.
Implementation idea
-------------------
At the point during processing at which an object (line, polygon, text) is
actually output to the final image the geometry data is captured together
with an user definable object property (object ID, street name, …) and
written to a metadata section. For more complex features post processing
might be required that combines features to reduce the amount of data.
Output format
-------------
I intend to make the output as flexible as possible. Probably there will
be different output methods for different needs. Some examples I can think
of:
- Writing the data to a database (PostGIS, etc.) which is queried when the
user clicks somewhere (for large scale projects/many clickable feature per
tile). This seems to be the way Google Maps works.
- Writing a file with geometry information and some kind of ID (e.g.
node/way-ID) or URL for each tile produced (for systems without a database
backend).
- Writing one big file for the whole area covered with preprocessed
description texts, that can be displayed as popup texts. Useful for small
or standalone systems without permanent internet connection. This format
would probably be directly compatible with OpenLayers vector layer [1].
- For SVG output it might be possible to add some more tags to SVG objects
which contain IDs. So the geometry is not duplicated.
- The project idea page in the wiki lists EXIF as a possible output
format. This might be well suited because all data is contained in one
file, but it's hard to read EXIF data in JavaScript which is the main
platform for clickable maps. I was able to find only one JavaScript EXIF
implementation and it doesn't work in all browsers.
Of course the implementation and output formats are open to suggestions.
Deliverables
------------
- Patches to add the required functionality
- Examples of how to produce clickable maps
- Tools to simplify this process and make it available to everyone
Timeline
--------
April 26: Accepted student proposals announced on the Google Summer of
Code 2010 site.
Community Bonding Period: Students get to know mentors, read
documentation, get up to speed to begin working on their projects.
I'll familiarize myself with the Mapnik codebase, discuss the formats,
requirements, etc. I expect to start coding during this period already
because this is usually a quiet time at university.
May 24: Students begin coding for their GSoC projects;
At this point I should be familiar with the code and write the basic
implementation (one output format).
I expect to be busy with exams directly before the mid-term evaluation,
but they should not last long.
July 12: Mentors and students can begin submitting mid-term evaluations.
I'll have a working code at mid-term. After that date I'll add more
advanced output options, configuration options and write documentation.
To help users of my code I'll create some examples how to use it with
OpenLayers.
August 9: Suggested 'pencils down' date. Take a week to scrub code,
write tests, improve documentation, etc.
All code will be ready, I can do some cleanups afterwards.
August 16: Firm 'pencils down' date. Mentors, students and organization
administrators can begin submitting final evaluations to Google.
August 20: Final evaluation deadline
I expect this timeline to be very conservative and I should have plenty of
time if unforeseen difficulties appear. If I'm done earlier I will work on
other things related to this project. Examples: Moving icons/text a bit
that can't be placed at the position it should go to because there is
another icon/text. Or combining multiple icons into one (however I'm not
sure this is easily doable as it will take two passes to place icons).
These improvements would help to make sure as many features as possible
are drawn and therefore maximize the amount of clickable objects shown.
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