Support transparent tile overlays

[Colin Marquardt]

A lot of OSM map providers use transparent tiles to show additional information. For instance on http://hikebikemap.de, I have a hillshading and a "By night" overlay, or Contours etc. It would be nice if OSN would support that.

Note that ideally multiple such overlays for a single basemap would be supported (e.g. hillshading with "By night" go well together). And, if you look closely, you can even add the hillshading tiles two times there - this is for flatter areas where it gives the map a more plastic look.

[chris_debian (cjhandrew)]

Sounds like a good idea to me, as long as it's open source.

Chris.

[chris_debian (cjhandrew)]

As long as it's open source, it sounds like a good idea to me.

Chris

[chris_debian (cjhandrew)]

Apologies for double post, G1 browser problems :-)

Chris.

[Colin Marquardt (ubuntu-marquardt-home)]

Well, the lighting tiles from hikebikemap.de/toolserver.org are CC-by-SA 2.0, same as the OSM data. hillshading (and the contours, where I have them) are made of NASA SRTMv3 data which is public domain. In terms of tile usage policy, I use the same that applies to the ones from osm.org, so no problem there (otherwise you would be in violation with osm.org already :)

The "lonvia" tiles are not mine, but since they are made from OSM data as well, it should be fine too. A different tile usage policy might apply there however.

If you want to take my overlay tiles and add them to OSN by default, that would be great. However, I was thinking that by "support" for such overlays you would allow the user to customize that by himself. This would most likely need a differentiation between "base tiles" and "overlay" to find the stacking order.

Cheers
  Colin

[Kieran Fleming (kieran-fleming)]

I think this is cool, but at the same time I'm worried about this feature putting more pressure on ram/network/storage. Ultimately this feature will lead to very useful visualisations and mashups so it's worth looking at :)

[Colin Marquardt (ubuntu-marquardt-home)]

Well, devices, storage and network are becoming better even as we speak :) And if it's optional, the user has the choice.

While I don't have hard facts to prove it, it might be that a combination of the alpha hillshading tiles (8bit PNGs) and a "flat" map style that has a reduced color set is actually a smaller combined size than having to use full-color PNG tiles because you have all kinds of mixed colors in tiles with both hillshading and map in one. Plus, the hillshading alone could be cached much more aggressively because it's static, and is useful for other flat map styles, not just the hikebikemap style.

[Colin Marquardt (ubuntu-marquardt-home)]

Also, related to bug 587030, the awesome Dane Springmeyer of mapnik.org has written a script called tileblender (http://mapnik-utils.googlecode.com/svn/sandbox/tileblender/) that allows generating a combined tile from base map and overlays. If OSN allowed custom tile URLs, this could be run on a user's webserver.