GRASS GIS always has been lacking proper meta data support. But that has changed with the (relative) new wx.metadata add-on, which includes advanced tools for metadata management according to ISO 19115. It was developed during the Google Summer Code 2014 by Matej Krejci and is available through g.extension for GRASS GIS 7.1. The main tool to create or edit meta data is the g.gui.metadata function.
Below I’ll walk you through the main steps to get and use this tool. For a more detailed explanation of the different options available in wx.metadata and the installation requirements, see the grass wiki page. Continue reading →
I wrote before about the MBtiles format, a convenient format to store tiled maps in a single portable sqlite database. Probably the easiest way to create them is with Tilemill, as described here. The format is supported by amongst others QGIS, but it is especially suitable for use with map viewers on your mobile device.
The format is now supported by various mobile map viewers, including e.g., Geopaparazzi and OruxMaps. One I like for its rich set of features is Locus Map Pro. I normally only write about open source, but I think the developer of this app deserves some credit for being one of the first (as far as I am aware of) to support the MBtiles format. Up to very recently you could only view maps in MBtiles format (similar to the other viewers mentioned above), but with the latest update support for the UTFgrid feature has been added.This basically adds interactivity to your map. Continue reading →
Sometimes you want to rescale a raster layer, e.g., to reduce the number of categories, or to create a common scale for different raster layers. Very basic of course, so you can expect to find an appropriate function in any self-respecting GIS software. Just be aware that different terms are being used for the same thing, e.g., scale in gdal, rescale in GRASS and normalize in SAGA GIS. Below a few ways to do this using my favourite GIS programs: GRASS GIS, QGIS, SAGA GIS or gdal. Continue reading →
What if you get a raster layer with number of people per raster cell, like for example the population layer from Afripop, and you want to convert it to a population density layer?
Well, obviously, you need to divide the number of people by the surface area of the raster cells. However, the surface area of the raster cells of an unprojected (lat/lon) are not constant; they decrease with increasing latitude. So what you need is a raster layer with the surface areas of the cells.
I thought I had seen a function in GRASS GIS to do this, but that might have been a typical case of the wish being the father to the thought. But anyway, it isn’t terribly difficult to calculate it yourself using the map calculator. Continue reading →
The maximum-entropy (Maxent) methods is one of the most widely used approaches for species habitat modelling. It has its own dedicated software, the Maxent software (written in java and therefore cross-platform). The software is easy to use and includes fairly a complete help file and tutorial. But things get better… Continue reading →
A quick note to myself (and whoever is interested :-))
Markus Neteler mentioned on the GRASS user mailing list a new library that came out that extracts valid data from within an OpenStreetMap input file. It is from the developer of Spatialite, and can be downloaded from here.