Spatialite, like any good spatial data management system, can build a spatial index for your layers. Using this index in your spatial queries will dramatically shorten the runtime for that query. The latest version of Spatialite offers a nice compact format for using a spatial index. To demonstrate, I created a point layer of 20,000 theoretical store locations, with sales data for each store, and a polygon layer of over 280 “local councils”. My mission it to sum up the total sales in each local council. So I need to find which stores are located in each local council and aggregate sales for those stores.
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Creating a random set of points is a standard GIS technique, used often for setting up sampling or monitoring locations. Among the tools in FOSS GIS software which offer this function are QGIS (in Vector -> Reseach Tools -> Random points) or GRASS (using the
v.random module). But suppose you need points spread randomly along a line feature? The R-project package of spatial functions called ‘sp‘ can do just that.
I visited the growing acacia tree seedling, and took some measurements and photos this week. Here are the results compared to last year.
The recent stable version of Spatialite, 3.0, supports linking to and importing Excel spreadsheet tables. Read on to see how it’s done.
Last week’s bike ride was out to the wadi where “my” acacia seedling is struggling to survive. I was very satisfied to see that, with the cool winter weather, the plant has become green and seems to be doing well. On my last visit, during the scorching summer months, the seedling looked totally dried out and dead, and I wasn’t sure it would pull thru. We haven’t had any rainfall yet, just the lower temperature was enough to allow the plant to start growing again. These thorny buggers have eons of evolution behind them, so I guess they know how to deal with the arid season. I’ll visit again later during the winter and take measurements.
This week’s morning bike ride took me west of the Arava highway along the trail called the “springs route”. I came across a small flock of storks – maybe 50-75 – still resting on a knoll, getting organized for today’s leg of their migration to Africa. As I approached, they lifted off and resettled further from the trail. Later in the morning, as I came out of one of the canyons, I was surprised by one of those impressive sites we get only in the fall: those few storks were part of a huge flock circling overhead, looking for thermals to gain some free altitude before their day’s flight south. Hundreds, maybe more than a thousand of these majestic birds, moving around in chorus.
It’s early September, a bit soon for large migrations. The Bedouins say that when the storks fly across earlier than usual, then Europe will be experiencing a severe winter.
Continuing my last post on using the spatialite tools and software on EL 6 and clones, here’s how I got the spatialite_gui to work.
Spatialite, built on the shoulders of the popular sqlite single-file database, offers a broad feature set of GIS analysis tools. Getting data into a spatialite database is a snap when you’re starting from a shapefile. But what about GPS data. Here’s a few tips on how to upload data from the standard “GPX” format into a spatialite DB.
Tim Sutton’s excellent post from last year gives a recipe for creating a professional looking color relief background map from elevation data, and using only GDAL tools. I’d like to suggest one additional procedure to his step-by-step guide.
The tried and true (command line) program for interfacing between GPS instruments and Linux workstations is gpsbabel. QGIS and GRASS for example use gpsbabel to pull waypoints and tracks into GIS layers. However, to get gsbabel working on Scientific Linux 6.0 requires jumping a few hurdles