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
Grass and ArcGIS use different conventions for the flow direction rasters created when processing a DEM to create watersheds. I need to convert a GRASS flow direction raster to the ArcGIS convention. Here’s how I did it.
Continue reading Flow Direction from GRASS to ArcGIS
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
Nearly every new phone or tablet these days comes GPS enabled. And you can choose any of a slew of apps to capture GPS waypoints and tracks. But how do you get these data into a GIS system? Several apps save the GPS data into an sqlite database, so using Spatialite to convert the locations to spatial layers is a piece of cake.
Continue reading Get your phone GPS data into a GIS format
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
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
In hydrology, a stream network is composed of segments or “reaches” which are arranged in a hierachy. There are several systems of ordering the stream reaches, the most popular of which is the Strahler or Horton number. GRASS GIS offers, alongside the watershed delineation tool r.watershed (discussed here), a set of addons for stream network analysis. We’ll examine how to use these addons, and how to use strahler ordering to improve the visual effect of a stream network map.
Continue reading Strahler stream order in GRASS
There are several PostGIS functions floating around to calculate the UTM zone EPSG code for points in Latitude/Longitude WGS84. However, Spatialite, based on Sqlite, does not support user created functions. So how can we get the same results in a Spatialite database?
Continue reading From Lat/Lon to UTM zone in Spatialite
I returned from a short bike outing with my ride captured as a GPS track. Along the way, I also grabbed the rest stops as waypoints. Both of these were downloaded from the GPS as *.gpx files. So I have tracks.gpx and waypoints.gpx. Now I want to push these layers straight into Spatialite, and do some calculations.
Continue reading Manipulating GPS tracks in Spatialite
Quantum GIS is marching ahead and the latest stable version, 1.8.0, provides some new features and improvements. RPM packages are already out for Fedora, but not yet for the Red Hat 6 clones like Scientific Linux 6. Compiling on your own isn’t hard, so if you don’t want to wait for the official package, here are a few pointers.
Continue reading Getting QGIS 1.8 running on Scientific Linux 6