Open Source Computing and GIS in the UK

Firstly, if you’ve seen this post before, apologies. It got lost in a previous re-organisation of the blog and I thought it was worth re-posting…

You can get free contour data for the UK from the Scottish Mountaineering Club website. It’s based on public domain NASA data, cleaned up by the club and made freely available. It comes in garmin .img format, in several zip files, which roughly represent areas of the country. See their web page for an explanation of the areas.

Edit: Leszek has some great alternatives methods and options for data- check the comments.

1. To convert the img files to something (more) useful, the best programme I’ve found is gpsmapedit. You need to register it to get the full functionality. This costs 42 euros (umm, about 32 pounds at the moment) but allows you to use the programme on up to four computers.
2. In gpsmapedit, click “open” or “add” and load up all the img files you want to convert. Note that they will be merged into one big file so for the sake of your poor computer, choose only the areas that you need.
3. Go to file/export/mapinfo file, select level “0″, this includes the minor contours (down to 10m) as well as the major contours (100m)
4. When it has finished exporting, you can shut it down. If you’re using mapinfo, then skip to step 6.
5. In ArcGIS, crack open ArcCatalog, and load the “Arcview 8.x tools” toolbar. Move your mapinfo files to a location on your computer that has no spaces in it’s path name and a short path. No really, do. It will crash otherwise. Choose the “mif to shapefile” converter. Alternatively, you could do this with ogr2ogr. See the website for usage.
6. The resulting file (mapinfo or shape) is in wgs84 projection, with the height values in feet, so for use in a British National Grid environment you need to re-project it. The height values are in the attribute field “label”, so add another field for holding the converted height and use the tool of your choice to convert the values in the “label” column to metres.

Note that this data is good for broad-based terrain modelling only. If you need something more accurate you’re going to have to buy it…

If you have any alternatives to this method let me know in the comments!

There’s an article on the All Points Blog that goes into more detail about the potential support for PostgreSQL/PosGIS in ESRI products. The caveats to this are listed below, and I have to ask- what’s the point guys?

It will only be in Enterprise ArcSDE- so you’ll need ArcGIS Server Enterprise Basic as a bare minimum, and of the windows products it will only work on Server 2000/2003. So- if you have loads of money to spend on your GIS you’ll be able to use PostGIS- but not if you don’t have thousands to spend.

It will contain it’s only spatial implementation alongside the PostGIS “spatial type”. So that will keep things clear and easy to follow then.

We had this debate ages ago, but it seems as if ESRI really haven’t listened. I guess it doesn’t matter that much to low-end users as there are alternatives but it seems like they are missing the boat. However apparently they are really interested in getting feedback at their non-existent forum so that’s OK…

I have just stumbled upon the ESRI Mapping Center and, while I had been following their rss feed for a while, I didn’t know about the wealth of useful information that they have been putting together for creating attractive maps. A lot of the tips can be applied to other software packages too- not just ESRI.

I particularly like the article on historical maps, or how to create an authentic looking treasure map. The section on “Ask a Cartographer” also looks promising, although there aren’t many questions up there yet. ESRI are also reissuing Eduard Imhof’s book Cartographic Relief Presentation, which is a bit of a classic in the field of cartography, so watch that space carefully.

BTW, in a low-key way I’m celebrating because this is the 50th post on archaeogeek. For those that know me and my short attention span, this is quite an achievement!

I have made a little more progress with evaluating the various free options for accessing PostgreSQL/Postgis database tables from ArcMap. I have to confess that some of the problem was down to my own lack of experience with Postgis!

The issue that I had with PGarc was that it would fail with an error if you had deleted tables from a database. It turns out that this is because deleting tables using the PostgreSQL “DROP TABLE” syntax does not remove it’s reference in the “Geometry_Columns” table. This must be removed as well- either separately or by deleting the whole shebang in one go using the Postgis DropGeometryTable function. Since PGarc uses “Geometry_Columns” to populate its list of available tables, it fails at this point. RTFM next time, archaeogeek!

There were a number of people in the google group with similar problems to me regarding ZigGis- namely that it would not display some layers. This turned out to be a problem with projections, or the SRID. If a table had an SRID of -1, in other words no projection set, then ZigGis could not display it. This bug has been resolved in the latest release.

My opinions of the two packages haven’t really changed. ZigGis has nice configuration files, and works directly with the Postgis table, whereas PGarc relies on DSNs, and creates a temporary shape file on your hard drive to work with. However, the clincher for me is that using PGarc you can select data and query it, whereas with ZigGis, I could not do that.

In the comments to my previous post, JeffÂ� kindly pointed out the trial version of Safe Software’s FME (Feature Manipulation Engine), which does include support for PostgreSQL databases. I haven’t had chance to try it out yet, and we are trying to work towards open-source solutions to our problems but I will evaluate it and post on my experiences.