In my previous article, I showed how you can convert point coordinates into a polygon vector layer in QGIS. So how about GRASS GIS? Like in my previous post, let’s assume you have a text file with two columns with the coordinates. With the v.in.ascii function you can import this text file as a point layer. Next, you can use v.hull or v.delaunay to create polygon layers.
In my previous post I described how to export a vector layer from GRASS GIS as kml file. The key was to use the dsco parameter to define the columns that should be used for the Name and Description fields in your kml file.
In QGIS you use the ‘save as’ option in QGIS. You can get this using the context menu (right click mouse on the layer) or the menu ‘Layer | Save as..’. In the menu that opens, there are two fields under the header ‘OGR creation options’; ‘Data source’ and ‘Layer’. Continue reading
v.out.ogr input=labels layer=1 dsn=/home/paulo/test.kml format=KML
will export the vector layer ‘labels’ as the kml file test.kml Continue reading
I have a large number of GRASS vector layers with in the attribute table a RGB column defining the colours of the corresponding mapping units. Unfortunately, unlike GRASS, QGIS does not offer the option to to set colours from an RGB column. The feature has been requested before, but it isn’t implemented (yet).
As an alternative, I want to create a R script that takes the RGB values from the attribute tables and uses this to create a QGIS style file (qml file). Continue reading
Suppose you have a vector layer in your GRASS GIS database and you want to find all duplicate values in one of the columns of the attribute table of that layer?
If you are using SQLite or PostgreSQL as the database back-end (and you should), this is easy using a SQLite statement. Suppose you have the table sp1th and the column value with duplicate values: Continue reading
A quick note on adding two columns with X and Y values in a vector layer in spatialite. Spatialite stores the information about the geometry in binary format in the ‘Geometry’ field.
You can use the Spatialite function AsText() to convert and extract these values as a Well Known Text (WKT), which is an easy to read format. If you for example have a spatial table ‘Waypoints’ with two columns ‘PKUID’ and ‘Geometry’, you can extract a column with WKT values using: Continue reading