Category Archives: GIS

Upstream drainage areas with GRASS-GIS

Some GIS software has the ability to calculate the upstream drainage area for every stream reach in a stream network. In the streams attribute table there will be a column with the total flow accumulation area upstream of each section (reach) of the stream network. Total flow accumulation is sometimes referred to as "adjoint catchments". GRASS-GIS lacks this capability, but with few quick commands we can overcome this and add total upstream drainage area to each stream reach within GRASS. Continue reading Upstream drainage areas with GRASS-GIS

QGIS fighting bugs

Real bugs, agricultural pests, cause damages to food production throughout the world. GIS techniques can help in monitoring pest infestation by collecting and mapping data from traps, baited with pheromone lures. QGIS when teamed up with Spatialite makes the ideal combination for pest control programs to maintain and display the distribution of different species of insects. Here’s how it’s done. Continue reading QGIS fighting bugs

Geostatistics and rainfall with R

With the rainy winter season behind us, it’s time to summarize how much precipitation we got this year. The southern Negev desert enjoyed above average annual rainfall (in stark contrast to the rest of the country, where we saw only 60% of the multi-year average)

I wrote about creating isohyetal contours some years ago. This time I’ll try to improve my interpolation by using the powerful, open source R statistics program.
Continue reading Geostatistics and rainfall with R

Spatialite helps creating an index of LIDAR tiles

We have a large set of LIDAR data, in separate *.las file, each covering a small rectangular area. I wanted to create a polygon shapefile of the coverage of each tile for reference so I know which files to choose when we need a subset of the whole region. Using a bash “one-liner” and a simple function in Spatialite I had my polygon layer.
Continue reading Spatialite helps creating an index of LIDAR tiles

Creating Depth-Volume curves with GRASS-GIS

Our regional Drainage Authority prepared a reservoir at the mouth of a small dry riverbed to catch and regulate flood water coming from a mountain canyon. This reservoir was to act as a buffer to prevent flooding of agricultural fields and residential areas further down the valley. After a sudden rainstorm last week, the reservoir bravely fulfilled (pun intended 😉 ) it’s duty. Now we want to know how much water was actually captured, and to create a depth volume curve for the small “lake” that was formed. Here’s how I did this using GRASS. Continue reading Creating Depth-Volume curves with GRASS-GIS

New Labeling in Quantum GIS

The new labeling setup in QGIS has been around for over a year now, and in the upcoming version it will become the default, replacing the old labeling. This new engine brings some advanced options that are quite worth learning, such as bulding labels from expressions, and conditional labeling. I’ll expand on some of these tricks that have already appeared in other QGIS blogs
Continue reading New Labeling in Quantum GIS