New downloads available

I'm happy to announce additional Shapefile downloads on openstreetmap.la:
those include buildings, national parks, provincial and national boundaries for Laos and Cambodia.
Please find all files at openstreetmap.la/downloads.

Two villages close to Pakxan with buildings displayed in QGIS.
Data © OpenStreetMap contributors

Nam Ngum 2 dam three year ago

Yesterday I found by chance a picture that is exactly three years old. I took it when I flew from Phonsavan back to Vientiane and it shows the Nam Ngum 2 dam under construction.

Nam Ngum 2 dam under construction on 21. November 2009

Heat maps with Python

Heat maps are a quite often discussed topic on gis.stackexchange.com, probably because they are easy to understand and very appealing when showing spatial distributions of features. Working with a Python web framework, I looked for a Python way to create heat maps. Finally I came up with a script that uses OGR to read an input Shapefile and matplotlib to do the actual work.

Editing GPX files with Garmin extensions

During my outdoor activities I often (not to say always) carry a Garmin GPS device with me. Nowadays current Garmin devices record also heart rate, pedal cadence or even temperature and write these data into a GPX file as extensions.

After my last cycling trip I edited (like I normally do) my tracks in viking, when I realized that all the additional Garmin data are lost. I tried to find another workflow without losing the data in the GPX extensions. Finally OGR was once more my big saver. For the following workflow OGR is required at least in version 1.8.

Native SLD support in QGIS

The current Quantum GIS master (i.e. the latest development version) supports now loading and saving of Styled Layer Descriptor (SLD) styles in the layer properties dialog.

The QGIS API has been extended by the new methods saveSldStyle and loadSldStyle in QgsMapLayer and writeSld and loadSld in QgsVectorLayer. Currently these methods are not yet available in the Python API, but it is simple to add them in the corresponding SIP files.

Line extraction with GRASS GIS

This post presents another way how to use Landsat imagery to map features for OpenStreetMap in an easy way with free and open source software only. After remapping the Nam Ngum 1, Nam Leuk reservoir and other lakes using a similar approach, I wanted to improve the Nam Ngum river. The second largest river in Laos and an important tributary to the Mekong was in OpenStreetMap only mapped as a single line instead of an area, although it's more than hundred metre wide downstream of the Nam Ngum 1 reservoir.

Armchair mapping using GRASS GIS

After reading my previous post a friend asked me why I didn't use just GRASS GIS. That's really a valid question. Since the GDAL/OGR utilities are some of my daily tools, I'm more familiar with them than with GRASS. Out of interest I developed a workflow how to extract and vectorize waterbodies from Landsat images using (almost solely) GRASS GIS. The resulting features I wanted to upload to OpenStreetMap.
This time the Nam Ngum 1 hydro power reservoir in Laos was my test area. Like Nam Leuk last time it was only roughly digitized and some of its islands needed to be remapped.

Armchair mapping with Landsat imagery

In this post I want to show step by step how I extracted hydro power reservoirs and lakes in Laos from up-to-date Landsat imagery for further use in OpenStreetMap. The extraction is done straightforward with common GIS tools but without sophisticated and/or proprietary remote-sensing software.
As an example I take the Nam Leuk hydro power reservoir in Laos. This reservoir needs to be remapped, since the origin user declined the upcoming license change. Currently the reservoir is rather roughly generalized.