Monday Oct 06, 2008

QGIS imports ArcInfo!

I downloaded some .e00 files from Maproom for my lovely PhD project today. The only possible way of converting these files into shapefiles seemed to be via the ArcCatalog conversion tool (which, very inconveniently, had to be set up and found first...).

First things first: I found this "handy" website which gives clever links to the ESRI website on how to do the above... They did not work, try it out!

The conversion tool worked fine for half the data, the rest just couldn't be converted, no matter how hard I tried, and when I finally managed through the AVCE00 ArcView converter ArcGIS crashed and died several times (surprised?)...

Opening QGIS was a good idea, as this reads the .e00 data without any difficulty. Simply click "Add a vector layer", selecting to show files of all types and adding the .e00 files. Slighlty unexpected, because it doesn't appear in the list of options. But that's about it, otherwise great, problem solved :-)

Wednesday Jun 25, 2008

Survey data inaccessibilities

Yesterday I got *slightly* annoyed. I went out to set out a site on Monday and due to the GPS not having great reception I unpacked our shiny (not new) Leica TCR705 Total Station. All went well, but when it came to downloading I got quite upset about the fact that this piece of equipment can by default only be downloaded using a programme called LisCad - the most user-unfriendly software in the world. I struggled for quite some time - as one does and finally managed to get my data out of the machine - thanks to my helpful colleagues who are a bit more familiar with it!

Issues are the following: The data from the machine is converted into a textfile, which is LisCad-specific and has to be exported into AutoCAD format to make it workable. Problem number two is that the points which are exported have none of the data attached to them which were previously attached to them during survey - HOW ANNOYING!

Then I downloaded the GPS (Leica 1200 system) data from the same day. All data from our Leica 1200's is downloaded using Leica GeoOffice (LGO). This software is a lot more userfriendly and convenient and actually exports points with data attached and produces data output in various working formats. It still creates the link between the instrument and the computer.

Furthermore it is complicated and inconvenient to transfer between software and instruments, e.g. the TCR705's line data cannot be imported into LGO which makes it all very instrument-specific and frustrating.

To be fair - Leica supplies us with all the software and the most up-to date stuff comes with each machine and one always receives new updates as well. Support is also granted. As one would expect when investing into very expensive equipment.

Then I started to think - what would happen if one had a piece of survey equipment and not the compatible software? or a computer which is too old? Or an operating system which is not compatible with the Leica software (or whatever make, I am not being negatively focussed on Leica)? Or no survey software at all? Or the software dies and support is presently unavailable?

What I am trying to say is the following:

a) I am not happy with the monopoly the survey equipment companies take over the software and downloading procedures.

b) The fact that raw data, in a universally accessible format, is very difficult to extract from the machines is a great nuisance.

This is all due to the fact that Leica and the likes have a monopoly over the data their machines produce.
I am aware of the fact that the data can be extracted without the use of prescribed survey-software, but this is currently quite complicated and under development.

Any suggestions for avoiding the use LGO and it's likes are very welcome!

Sunday Jun 08, 2008

How to create contour lines in open source GIS

I was given the task to create contour lines for three sites close to one another. The levels had been previously surveyed and existed as shapefiles. Here is what I did:

Programmes used (in this order):

GvSIG: Upload the level shapefiles. Then start the Sextante extension toolbox and choose: “Rasterization and Interpolation” - “Kriging”. Under “Parameters” choose the point input layer – the individual level shapefiles. The “Field” should be the one containing your height info. Select a filepath for the output “Result[raster]” and save it somewhere obvious – it will be used in the next step. In the “Raster output” tab choose “use extent from layer” and define your cell size (not too small). “Accept” - a raster image is added to your dataset which contains the height information Create as many raster images as required (in my case 3).

The next step takes place in MapWindow, because I discovered that although GvSIG produces them it has 2 major problems: a) The height of the individual contours does not seem to recognize them and rounds everything to the nearest meter – not very useful. b) GvSIG creates an outline around the extent of the contour shapefile, which has to be painfully cropped away.

Therefore we change to

MapWindow: Got to: “GIS tools” - “Raster” - “Generate a contour shapefile”. Choose: “use an external file...” and browse to wherever you saved the raster image produced by GvSIG, add it. You can choose an output shapefile or save the contours later. Then define your contour interval or “use fixed levels” - you will probably have to go through this process until you are happy with the result. “Generate” and the contour shapefile will be created and added. Create as many shapefiles as required (in my case 3).

Another problem I encountered was when I tried using MapWindow to crop the contour shapefiles to the boundaries of the three areas. One area consisted of several polygons and the “Clip shapefile with polygon” in “GIS tools” - “Vector” did not work for this one. I think it does work if your area consists of one polygon only, though.

Thus I put the boundaries and the contours into

GvSIG again and use the “View” - “Geoprocess toolbox” - “Geoprocesses” - “Analisis” - “Overlay” - “Clip” Select your Input- and Clip- covers and save the new shapefile – it will be cropped to match the boundary of the area.

OpenJump: Is handy to select individual polylines from your contours, copy these and export them to new shapes in order to be overlain to the rest and labelled. Right-click onto your layer - “Select current layer items”. Once that has been done, go “Edit” - “Replicate selected items” - they are then added to your dataset and can be saved as a new shapefile.