Difference between revisions of "Tips and Tricks"

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* QGIS homepage:  http://qgis.org
 
* QGIS homepage:  http://qgis.org
 
* GDAL homepage:  http://www.gdal.org
 
* GDAL homepage:  http://www.gdal.org
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Here is a nice tutorial for editing vectors using QGIS as a frontend to GRASS: [http://grass.osgeo.org/grass-wiki/Editing_GRASS_vectors_with_QGIS Editing Grass Vectors using QGIS]
  
 
To use the two together, the GDAL-GRASS plugin must be installed:
 
To use the two together, the GDAL-GRASS plugin must be installed:

Revision as of 07:00, 16 February 2009

Tips and Tricks

Using QGIS as a frontend to GRASS

  • QGIS started as a simple viewer for geodata. And that's really what it still is: a simple-to-use geodata viewer with some editing capabilities. That's what it was designed to be and that's what it can do really well. QGIS does not have built-in capabilities for geodata processing and analysis.
However, a while back, Radim Blazek, who was then a core developer of the GRASS 6 system, decided to write a plugin for QGIS that would make it possible to access GRASS functionality from within the QGIS GUI.
And that's what you get today, when you download a binary version of QGIS for your platform: QGIS + GRASS 6 plus a plugin that makes using GRASS from QGIS simple and fun.


QGIS can run as a frontend to GRASS. There is support for displaying maps, editing maps, and execution of simple GIS functions. The GDAL/OGR library is a requirement for that (but for GRASS anyway):

Here is a nice tutorial for editing vectors using QGIS as a frontend to GRASS: Editing Grass Vectors using QGIS

To use the two together, the GDAL-GRASS plugin must be installed:

Test that the GDAL-GRASS plugin is available with this command:

  gdalinfo --formats

Look for a line like "GRASS (ro): GRASS Database Rasters (5.7+)"

Enable the QGIS GRASS plugin from QGIS:

  GUI: Plugins / Plugin Manager / Check the GRASS checkbox

The GRASS toolbar should now be visible. While not a firm requirement, it is easier to start QGIS from within a GRASS session.

Importing SRTM30plus data

SRTM30plus data consists of 33 files of global topography in the same format as the SRTM30 products distributed by the USGS EROS data center. The grid resolution is 30 second which is roughly one kilometer.

Land data are based on the 1-km averages of topography derived from the USGS SRTM30 grided DEM data product created with data from the NASA Shuttle Radar Topography Mission. GTOPO30 data are used for high latitudes where SRTM data are not available.

Ocean data are based on the Smith and Sandwell global 2-minute grid between latitudes +/- 72 degrees. Higher resolution grids have been added from the LDEO Ridge Multibeam Synthesis Project and the NGDC Coastal Relief Model. Arctic bathymetry is from the International Bathymetric Chart of the Oceans (IBCAO).

All data are derived from public domain sources and these data are also in the public domain.

GRASS 6 script r.in.srtm described in GRASSNews vol. 3 won't work with this dataset (as it was made for the original SRTM HGT files). But you can import SRTM30plus tiles into GRASS this way:

r.in.bin -sb input=e020n40.Bathmetry.srtm output=e020n40_topex bytes=2 north=40 south=-10 east=60 west=20 r=6000 c=4800
r.colors e020n40_topex rules=etopo2
Source
GRASS Users Mailing List http://grass.itc.it/pipermail/grassuser/2005-August/030018.html
Getting SRTM30plus tiles
ftp://topex.ucsd.edu/pub/srtm30_plus/data

GMT (The Generic Mapping Tools)

GMT (Generic Mapping Tools) is a Free software package for creating publication quality cartography.

GMT homepage: http://gmt.soest.hawaii.edu

Interfacing R-Statistics with GRASS

GRASS may be combined with R-Statistics to create a very powerful geostatistical analysis platform.

R-Statistics homepage http://www.r-project.org

Using GRASS with an on-line Web-GIS

see:

(please expand)

Starting and running GRASS from a script

See GRASS and Shell.

Running GRASS remotely on OS X

Tiger (OS 10.4) changed the default configuration of SSH from previous versions of OS X. You can no longer start an ssh session with the -X flag and display the Tcl/Tk components of the GRASS GUI remotely. If you are running grass on OS X (10.4) between hosts on a network (i.e. running it on one machine but displaying it on another), you will need to use the "trusted forwarding" mode of SSH in order for the Tcl/Tk generated graphics, such as d.m or gis.m in order for the GUI graphics to make it through your connection. This can be done using the -Y flag when you start the ssh session:

ssh -Y remotehost

or add this to ~/.ssh/config:

Host hostname
  ForwardX11 yes
  ForwardX11Trusted yes

Using the -X flag, or simply turning on X11Forwarding in the SSH configuration files, is not enough: the symptoms in this case are that a d.mon window will function fine, but none of the Tcl/Tk dialogues will work, failing with an error message complaining either about Wish not behaving as expected, or a "Bad Atom".