How to use tiles in this strange tiling scheme?

Question

I'm looking at cell coverage maps such as this one, and trying to figure out how to get a GIS program to use it as a source of information. Ultimately, I need to be able to combine the output with other cell coverage maps from different sources. But in order to do that, I need to understand how each one works and how to align them with each other.

Strangely, each of the five zoom levels offered has a different tile size:

1. 160x160 pixels
2. 128x128
3. 145x145
4. 198x198
5. 182x182

I've never seen a map tile service like that before. Usually the tile sizes are all the same. Do map-service-consuming tools (I'm thinking of open-source tools like Tilecloud) have the ability to consume maps whose layers have different - practically random - tile sizes?

Additionally, I'd like to know how the tiles are georeferenced. Maybe that's not exactly the right way to say it ... but I need to be able to combine tiles from different maps so that they're aligned properly.

Maybe I could get the information needed for that if I knew what kind of map tile API is being implemented by http://gsma.streetmap.co.uk/custom/barts/gsma/. Maybe they have a REST URL that gives data about spatial reference and so on. But I haven't been able to figure out what API they're implementing.

Using the browser debugging tools, I see URLs like http://gsma.streetmap.co.uk/custom/barts/gsma/gmap.srf?o=1&i=502/951/Zoom3/Zoom3_502_Tile007_9511638.png for the tiles.

The mobileworldlive.com page loads several javascript files, including two from gsma.streetmap.co.uk: http://gsma.streetmap.co.uk/custom/barts/gsma/SMJ_GSMA.srf?id=502&layer=951&nd=http://mobileworldlive.com/maps/images/map_na.jpg and http://gsma.streetmap.co.uk/SMJ_ObsEmo.js (The first one has an "include" that loads the second.)

They contain a bunch of custom map display code. I suppose I could try to learn about the API through reading that code, but that seems like a time-consuming and error-prone way to do things if this is implementing an API that's documented somewhere.

Thanks for any suggestions on how to attack this.

Answer 1

One way to convert odd TMS sources to something usable is MapProxy.

What you want to do is define a tile source with a custom grid and set up a cache which uses your source. Once it's in a cache you can set up an output service with a standard TMS grid, or use WMS, WTMS, or another supported option.

The two tricky parts are going to be

1. Determining your grid. You may need to define multiple grids, one for each zoom. You'll have to figure this out yourself, as you've got some very strange sources. There is code out there for defining a grid from ESRI MapServer meta-data, but you've just got weird layers

2. Getting edges to match if some layers don't have alpha on the areas outside their extent. This is always a pain.

I really doubt there's anything out of the box that will work with that tiling scheme without having to define what the scheme is, it looks to be something completely non-standard.

Don't forget to mind the terms of service, and set reasonable concurrency limits on the downloads from the source.