Cloudless Atlas Laos 2020

To track down new hydro power reservoir and schemes I've downloaded most 2020 Landsat 8 scenes of northern Laos and applied my cloudless script.

Northern Laos

The Nam Ngiep Hydropower Scheme

Just recently I continued mapping the Nam Ngiep hydropower scheme, see also my previous post about Nam Ngiep 1.

So far my findings:

Nam Ngiep1

Yet Another Hydropower Dam: Nam Ngiep 1

Meanwhile Nam Ngiep 1 dam has been completed and the reservoir has been filled during rainy season in 2018. I.e., it's high time to put in on the map!

Nam Ngiep 1 reservoir area in January 2018

New hydropower dam: Nam Phay

Just recently I've put the Nam Phay hydropower reservoir on the map!

During Lao New Year 2014 I had the chance to visite this area, see pictures below:

The Nam Phay reservoir area in Januar 2015

Another Hydropower dam: Xekaman 1

Just recently I've found by chance the Xekaman 1 hydropower reservoir on Landsat 8 imagery. Time to put it on the map!

The Xekaman river area recorded on 24th January 2015, just before water storage started

Raster math in GRASS GIS using numpy

Houay Lamphan Gnai, yet another hydropower plant just started commercial operations recently with a reservoir area of seven square kilometers as reported by local media. Time to put it on OpenStreetMap using up-to-date Landsat 8 imagery and the new GRASS GIS 7 plugin for QGIS 2.12. To get familiar with GRASS GIS' interface to numpy, I've decided to extract the reservoir using numpy.

Houay Lamphan Gnai on Landsat 8 image taken on the 23rd Oct, 2015

Web Map Service with PyCairo and Pyramid

From time to time I have the chance to work with PyCairo, the Python bindings to the cairo graphic library. I appreciate this library because it allows to draw graphics primitives so super fast and thus it is very suitable to use it in web projects.
After my trials with GRASS GIS as WMS backend I thought I could create a raster web map service with improved performance by using PyCairo instead of GRASS GIS as renderer.

Zoom in - it is a super fast WMS!

Imitating MapBox' Cloudless Atlas

Inspired by several posts which explain MapBox' marvellous Cloudless Atlas, I wanted to imitate a cloudless atlas by myself. Limited in time and computer power I had to do it much simpler of course. But using first class spatial Python libraries I could achieve quite nice results with a simple Python script.

The result: a cloudless Landsat 8 scene

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.

Rivers and lakes downloads available on openstreetmap.la

During my two-week trip through Laos I collected some tracks and points of interest, of course ;). Last week I started to add them to OpenStreetMap when I realized that there are still a lot of rivers missing. I traced (rather randomly) some parts of rivers from Landsat or where available Bing imagery.

Power lines from Landsat imagery

Hydropower is the big deal in Laos at the moment and therefore power lines are required. Some weeks ago on an offroad ride we crossed the relatively new Nam Ngum 2 power transmission line. Realizing the long straight and wide forest aisle, I knew that it must be possible to identify the line on Landsat imagery to map it on OpenStreetMap. Landsat imagery is in the public domain and thus suitable for mapping.

I downloaded the Landsat imagery from January and February 2011 for this region already earlier. Therefore I could start mapping the power line immediately, starting from the point where the power line crossed our way and following the forest aisle on Landsat. It's probably the first mapped power line on OpenStreetMap in Laos.

Nam Ngum 2 dam and power lines on Landsat

There is the Nam Ngum 2 reservoir and its dam visible in the middle at the top border. In the lower left corner is the older Nam Ngum 1 reservoir. The power line going south is clearly identifiable in the middle section. Furthermore two access roads to the dam are identifiable, one on the north shore of Nam Ngum 1 and one leading east from the dam. Just downstream of the new dam there is the confluence of Nam Bak.

Just for the visual appearance I tweaked the image to get rid of the stripes using GDAL, GIMP and OSSIM. OSSIM is as fas as I know still the only FOSS that implements histogram stretch based on the standard deviation.

The power lines in natura