On Apr 2, 2010, at 12:11 PM, Eric France wrote:
Dane,
Thanks for the pointers, I'll dig into them.
you are welcome.
I think the annotation you are pondering would be an excellent
addition to Mapnik, for myself and anyone else who has moved beyond
the "feeding-tiles-to-OpenLayers" feature of their mapping
application, and needs complete printable map images for reporting
and document production.
yep. the pressure is mounting. For a few years now I and others have
solved these issues through programmatic tools, which is powerful and
rewarding. But at the end of the day, friendly ways to do it will be
welcome I think by all. Just a tricky thing to design right. Thanks
goodness the Mapnik community is so wicked smart :)
- dane
Eric
From: Dane Springmeyer <[email protected]>
To: Eric France <[email protected]>
Cc: Mapnik Users <[email protected]>
Sent: Fri, April 2, 2010 2:36:20 PM
Subject: Re: [Mapnik-users] Layer In Pixel Coordinates?
Eric,
I've been pondering some kind of 'Annotation' or otherwise screen
pixel coordinated based datasource plugin or feature, so its good to
hear this would be useful as I think it would meet your need in a
generic, simple way perhaps.
But, likely a better approach for most cases and the only easy way
now is to draw directly on the map surface in screen coordinates
after rendering the geographic features on it. Mapnik does not
currently support any way for users to do this after rendering a png/
jpeg with the agg_renderer, but it is quite easy with the
cairo_renderer (which supports png,pdf, svg). You basically render
your map to a cairo context, then draw further on that context with
pycairo (of course learning pycairo from scratch is not terribly
easy but its a fairly good api).
for inspiration see:
http://oliverobrien.co.uk/2010/03/map-adornments-with-cairo/
and also a simple example here that shows drawing a neatline and
title:
http://mapnik-utils.googlecode.com/svn/sandbox/testing/cairo_contexts/render_to_context.py
Please post back your progress to the mailing list or the trac wiki!
Dane
On Apr 2, 2010, at 9:16 AM, Eric France wrote:
I want to create a map legend box that will be rendered in a layer
above all the other map layers, using the same shapes mechanism
that I'm using for the geographical information. However, I want
to render the legend box in the same location in the bounding box,
no matter what lat/lon coordinates are being rendered.
It seems that the simplest way would be to have a layer whose
coordinate system is in absolute viewport pixels rather than
whatever projection the GIS shapes are rendered in (I'm using
"+proj=latlong +datum=WGS84" for everything else). Can I change
the proj and datum values to image pixel x,y for a single layer,
and if so, what are the proj and datum keys?
Or is there another way to do this?
Eric
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