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[route-me] A few more question regarding custom tile sources Thomas Winkler Wed Jun 24 07:00:23 2009


is there any documentation on how to integrate custom tile sources? I  
couldn't really find anything except for some bits and pieces on this  
mailinglist, so I'm currently playing around trial and error style.

Here's my situation: I have custom tiles for an area of about 30,000  
sq mi which I'd like to use with route-me (so I do not want to show  
the whole world in my App but a specific area). The tiles are  
available in 4 different zoom levels:
Zoom 0: 24 rows and 16 columns
Zoom 1: 96 rows and 64 columns
Zoom 2: ~192 rows and 128 columns

Currently, I'm playing around with the SimpleMap example and modifying  
RMOpenStreetMapsSource.m to load the tiles from the custom tiles  
server instead from openstreetmaps. I got it working with a fixed zoom  
setting of kDefaultInitialZoomLevel = 5.0 (defined in RMMapContents.h)  
while requesting custom tiles with zoom 0 from the server (so, the  
framework thinks it's using zoom level 5 but I have modified the  
tileURL method to return a URL for zoom level 0 of my custom tiles).

I had a closer look at the OpenStreetMap tiles and found out that the  
zoom levels look something like this:
Zoom 0: 1 row and 1 column (whole world is in one tile)
Zoom 1: 2 rows and 2 columns (whole world is on 4 tiles)
Zoom 2: 4x4
Zoom 3: 8x8
Zoom 11: 2048x2048
Zoom 15: 32768x32768

So, obviously both tile sources do not only use different zoom levels  
but also my custom tile source doesn't have the same amount of rows  
and columns like OpenStreetMap seems to have.

Question 1: I assume the framework has to know for each zoom level how  
many tile rows and columns there are but couldn't find it anywhere in  
the source code. Any hints?

Question 2: How does the framework know which Lat/Lon corresponds to  
which tile? I assume this has to be initialized somewhere (e.g. center  
of tile 0/0 at zoom 0 is a specific Lat/Lon), but where and how? My  
custom tiles are only available for a specific area on the globe so I  
guess I have to tell the framework where it is so that I can place  
markers etc.

Question 3: As you can see above, the OpenStreetMap zoom level always  
quadruples from the previous level (e.g. at level 0 the whole world is  
on 1 tile, on level 2 it's 4 tiles, 16 tiles etc.). My custom tiles  
are a little different: zoom level 0 has 16 columns, level 1 has 64  
columns, 2 has 128 columns etc.  Is there an easy way to handle this  
different zoom factors with route-me?

Thanks, Thomas

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