Good news for QGIS MapInfo users


So some good news for QGIS users who also need/want to use MapInfo.  QGIS via GDAL 2.0 can support MapInfo TAB file editing. In all older versions of GDAL there was only support for read and/or write but not both.

MapInfo TAB editing has been supported in GDAL 2 but up until this point QGIS has only be built against GDAL 1.xx.  GDAL 2.x is now the default GDAL release in OSGeo4w.

From Jurgen:

2.0.2 is now the default GDAL in OSGeo4W and the nightlies (qgis-ltr-dev,
qgis-rel-dev and qgis-dev) already picked it up.

With the next release the regular packages (2.14 and 2.8) will also be updated
to use it

Even if you don’t want to make the switch to full QGIS you can now use both bits of software and edit in both.

QGIS will still only support a single geometry type per layer so if you open a mixed tab file you will get the geometry type selector.  You can load the layer 3 times if you need the 3 different geometry types.

 

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Generating contours using GDAL ( via shell or QGIS)


I tell you. It always amazes me how much cool stuff you can do with great open source GIS software these days. GDAL is one of those great open source projects that I have just found a great use for (apart from just opening every raster type under the sun in QGIS).

GDAL has the ability to generate contours from a DEM, something that I have always wanted to try for my town but have never been able due to lack of a good DEMs.

Recently we purchased a set of DEMs that cover a large area as part of a study. Each DEM uses a grid size of 1mx1m. Prefect for generating contours.

Using the GdalTools QGIS plugin.

First make sure that you have the latest version of the GdalTools plugin installed (GdalTools should be installed by default with QGIS. If it’s not, search “Gdal” in the plugin installer). Enable the plugin once it’s installed.

Load the DEM into QGIS using the Load Raster icon.

DEM loaded in QGIS

Now head up to the menu Raster->Extraction->Contour

Raster menu in QGIS

Select the settings that you need. For this DEM I am going to generate 250mm contours.

Contour dialog.

Take note of the text area at the bottom of the dialog as that is the exact command sent to GDAL in order to generate the contours. If you take a copy of that you can run it on the command line for batch processing later.

Hit ok.

250mm contours from the DEM

BAM! :)

Using the command line/shell.

Using QGIS for a one off DEM is fine and dandy but what if you have 3000 DEMs that you need to process. To hell with doing that by hand!

Remember the contour tool in QGIS told us the exact command line args to use, so creating a shell script for automating the process is pretty easy.

for f in *.asc
do
  echo "Processing $f"
 gdal_contour -a ELEV -i 0.25 $f $f-250mm.shp
done

The above code will loop though the current directory and process all the DEMs generating 250mm contours for each one. It saves each new contour file as {filename}-250mm.shp. You will need to change *.asc to whatever format your DEM is in.

Copy the above code into a file somewhere and call it generate_contours.sh. This can then be called from the command line using

sh generate_contours.sh

Running sh on Windows

If you’re a windows user you will need to run OsGeo4W Shell in order to use sh.

Loading OsGeo4w shell.

Once the shell is loaded you can just call:

sh generate_contours.sh

Output from running generate_contours.sh

Final remarks

I ran the above sh script on a folder with about 2500 DEMs and it took around 4 hours to complete the whole folder. Of course performance will vary but it seems pretty quick considering.

Once again the possibly to use open source GIS tools to get my work done is amazing.  No expensive software here.

So far I’m not aware of any line smoothing/generalizing abilities using GDAL/OGR.  Although you can import the contours into GRASS and use that: http://grass.osgeo.org/wiki/V.generalize_tutorial

You can also generate the contours using GDAL via Python but that is a topic for another day.

Another cool open source project – OSGeo-Live


Another cool open source project that I have become a part of (as a QGIS packager and tester) is the OSGeo-Live project.  The OSGeo-Live project is a live DVD/USB/Virtual Machine built on xUbuntu(striped down Ubuntu linux) that has a lot of cool open source geo spatial programs all set up and ready to use.

The OSGeo-Live project contains:

  • Browser clients
  • A small sample of crisis management software
  • All the popular database engines (PostGIS, SpaitalLite etc)
  • Pretty much all the open source desktop GIS apps (QGIS, uDig etc)
  • Open Source GPS navigation apps and globes.
  • A collection of handy spatial tools
  • A ready to go web services ready to try in your browser or desktop GIS.
  • Some sample data to get started with for each project
  • And quick starts for each program.

The full list of software contained on the OSGeo-Live project can be found at http://live.osgeo.org/en/overview/overview.html

This is a good project if you want to get into the OSGeo tools and experiment but don’t want to install them on main machine until you know what you need.

As it is a live DVD/USB/Virtual Machine some apps will run slower than what they do on a native install but overall the speed is usable and good enough for testing.

Even better is that it was born in Australia :)

The project is also commercial supported by a Australian company http://lisasoft.com

So give it a try if you are interested in the OSGeo movement, which you should be if you are reading my blog :)

3D DXF from MapInfo Tab or ESRI Shape (or anything) using OGR


Note:The following post requires gdal 1.8

A lot of times we need to send/use 3D dxf files, we used to use FME however FME is not free or cheap. So I went looking for a free solution.

If you have gdal 1.8 it’s just one simple command line run using, what is becoming my favorite GIS tool, ogr2ogr.

All you have to do is run:

ogr2ogr -f "DXF" {outFile} {inFile} -zfield {ColumnWithZValue}

So in my case I ran:

ogr2ogr -f "DXF" C:\Temp\contourswarwick.dxf C:\Temp\Contours.TAB -zfield Height

I haven’t fully tested it but {outfile} can be any file ogr supports.

and the output:

Top view of contours
Top view of contour layer
Contours side view
The side view of the above image.

In the words of, the not so great, Charlie Sheen. WINNING!

Happy mapping :D