Tag Archives: gis

Getting information from IPs


Posts come very slowly, but here’s another one.

This post won’t be useful for most people :-(. You know when you use google analytics and get that fantastic map showing where people connect from? Read this, and you will learn how to do it yourself.

Tell me how


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Filed under code, curious, gis, Maps

Color to attribute. Qgis 2.X


In 2012 I created a small plugin for Qgis1.x. It allowed you to modify a vector layer, creating a new column to hold the color of the features. This proved useful for me at the time. I could use Qgis to decide the color palettes and then export to wherever I wanted.

Come 2013, a new version of Qgis appeared, and the plugin broke. I wasn’t using it at the time and I didn’t realize it. But someone did, and kindly pointed me to the problem. I don’t have as much free time as I used to. However as my grandma used to say “better later than never”, here we have the plugin to work with the 2.x series!.

You can get it from my github. The master branch has the original code, and there is a new qgis2.0 branch with the new revamped plugin.



Filed under gis

Convex Hull, one algorithm implementation

I talked about convex hulls some time ago in an alpha shape post.

The convex hull is probably one of the most basic computational geometry algorithms, and because of that it is present in almost, if not all, geometry/cad/gis libraries and software packages. In this post you will find an explanation of one of the existing algorithms to compute it, an implementation with C++, plus a set of scripts to generate various point clouds and the corresponding hulls.


  • Describe one of the possible convex hull algorithms
  • Implement the algorithm in C++
  • Provide various scripts to generate random point clouds and compute its convex hulls

I won’t lie to you, this post might be boooring ;-).

continue to this long post


Filed under code, gis

Basic Network Analysis With GRASS

I performed a little network analysis with ArcGIS on the Schools in Enschede. Given a shapefile with roads and the school points I obtained the service areas at 1km and 2km from the schools. Can I obtain the same with GRASS?

Brilliant! I want to read more


Filed under gis

α – Shape generation with R

α-shape, is a family of piecewise linear simple curves in the Euclidean plane associated with the shape of a finite set of points.
— Wikipedia

Boum!. Let’s make it simpler. α-shape is a generalization of the convex hull concept. And the convex hull of a set of points is the minimal convex set containing all the points. Is typical to depict as some pins covered by a rubber band.

convex hull

Representation of convex hull idea

α-shape me!

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Filed under code, tips, tools