TileMill and Ocularis

A long, long time ago, I discovered TileMill. It’s an app that lets you import GIS data, style the map and create a tile-pyramid, much like the tile pyramids used in Ocularis for maps.

tilemill

There are 2 ways to export the map:

  • Huge JPEG or PNG
  • MBTiles format

So far, the only supported mechanism of getting maps into Ocularis is via a huge image, which is then decomposed into a tile pyramid.

Ocularis reads the map tiles the same way Google Maps (and most other mapping apps) reads the tiles. It simply asks for the tile at x,y,z and the server then returns the tile at that location.

We’ve been able to import Google Map tiles since 2010, but we never released it for a few reasons:

  • Buildings with multiple levels
  • Maps that are not geospatially accurate (subway maps for example)
  • Most maps in Ocularis are floor plans, going through google maps is an unnecessary extra step
  • Reliance on an external server
  • Licensing
  • Feature creep

If the app is relying on Google’s servers to provide the tiles, and your internet connection is slow, or perhaps goes offline, then you lose your mapping capability. To avoid this, we cache a lot of the tiles. This is very close to bulk download which is not allowed. In fact, at one point I downloaded many thousands of tiles, which caused our IP to get blocked on Google Maps for 24 hours.

Using MBTiles

Over the weekend I brought back TileMill, and decided to take a look at the MBTile format. It’s basically a SQLite DB file, with each tile stored as a BLOB. Very simple stuff, but how do I serve the individual tiles over HTTP so that Ocularis can use them?

Turns out, Node.js is the perfect tool for this sort of thing.

Creating a HTTP server is trivial, and opening a SQLite database file is just a couple of lines. So with less than 50 lines of code, I had made myself a MBTile server that would work with Ocularis.

tileserver

A few caveats : Ocularis has the Y axis pointing down, while MBTiles have the Y axis pointing up. Flipping the Y axis is simple. Ocularis has the highest resolution layer at layer 0, MBTiles have that inverted, so the “world tile” is always layer 0.

So with a few minor changes, this is what I have.

 

I think it would be trivial to add support for ESRI tile servers, but I don’t really know if this belongs in a VMS client. The question is time was not better utilized by making it easy for the GIS guys to add video capabilities to their app, rather than having the VMS client attempt to be a GIS planning tool.

 

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