Let’s go to Bonn

It’s time for code sprint in Bonn.
I haven’t been on a code sprint before so it will be exciting.

I have 2 projects that I plan to put effort in, PostGIS and TilelessMap. I haven’t contributed to PostGIS for some years, but I like to identify myself as “core contributor” so I have to do something about it to earn the title. In PostGIS I have mainly 2 functions that I will add to the project.


ST_FilterM, which just filters the vertex points on the m-value. That is usable primary in combination with ST_SetEffectiveArea (which I think was my last contribution to PostGIS). ST_EffectiveArea is the same function behind the scenes as ST_SimplifyVW, but ST_SimplifyVW does the filtering at once. Those functions calculate an “effective area” for a vertex point by using the Visvalingam-Whyatt algorithm. A high effective area means that the vertex point has a high value for describing the geometry. A vertex point on the line between two other vertex points have 0 effective area and can be simplified away without affecting the shape of the geometry. The function ST_SetEffectiveArea saves those areas in the m-dimmension of the geometry. Then, by using the new function ST_FilterM it is possible to simplify geometries very fast without doing any calculations, by just looking at the effective area in m.

ST_ChaikinSmoothing is the next new function. The other day a colleague asked me it was possible to implement Chaikin’s algorithm for smoothing geometries in PostGIS. Chaikin’s algorithm is very simple and very smart. Take a look her. I do now have it working, but need to add documentation and look it over.


My next project is TilelessMap. It is a small map client reading data from SQLite rendering in openGL es2. I have tested it on Linux, Android and Windows (with some hassle on Win). So far it has been a project of my own, but I really hope to get more people interested to dive in. I think the concept have potential. I know of no other mobile app that handles large data sets of spatial data for offline use in a structured way. The Android app is now on F-droid.

Get it on F-Droid

I have also put together a map project for Bonn that can be found here. It is not fully styled as you can see by the screen shot at the bottom of this post, but it will help me at least to find my way (Warning, here is no road names on it).

What I hope from the code sprint about TilelessMap is to find some people interested in taking part of the project. I hope I get the chance to explain what it is and it’s potential compared to other approaches for mobile mapping. There are a lot of topics to discuss and to work on, both coding and documentation.

Hope to see you in Bonn!

Sceenshot of TilelessMap from Bonn.

2 thoughts on “Let’s go to Bonn”

    1. PostGIS is an extension to PostrgeSQL database to enable spatial capabilities. See https://postgis.net
      Tilelessmap is a project I have started to pack data with twmk format into sqLite databases and render them with openGL in Android, Linux, Windows or whatever

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