Category Archives: Uncategorized

Adding an arrow to an OSM map

Should be easier than this I reckon, but here’s how to do it and it’s hardly hard:

Quantum GIS – using a USB GPS device

In reposnse to an email question on the TZGISUG list “I am trying to get my Garmin GPS etrex Vista HCx to communicate with Quantum GIS through my pc with window 7. I will appreciate your comments and tips on how to get this working. Mtemi H. Miya M.Sc.”:

First of all, check the following:

  • Your GPS communicates with your PC normally, e.g. using MapSource, Google Earth or GPS Utility.
  • You have the “GPS Tools” plug-in for Q-GIS.
  • You have GPS Babel installed (I THINK this happens as part of the Q-GIS installation).

In GPS Tools, the default GPS device is a Garmin serial connection; so if you have a serial cable and connector, you’re in luck. However, most of us now have USB cables, which complicates matters. You need to define a new GPS device in GPS Tools, as follows:

  • GPS Device > Edit devices > New device >
  • Name = Garmin USB (or whatever name you want)
  • In the following six command lines, paste in the following (user-friendly, eh?!)
  1. %babel -w -i garmin -f usb: -o gpx -F %out
  2. %babel -w -i gpx -f %in -o garmin -F usb:
  3. %babel -r -i garmin -f usb: -o gpx -F %out
  4. %babel -r -i gpx -f %in -o garmin -F usb:
  5. %babel -t -i garmin -f usb: -o gpx -F %out
  6. %babel -t -i gpx -f %in -o garmin -F usb:
  • Update device > Close

Then still in GPS Tools:

  • Set the GPS Device to the new one you’ve just made (in this case, Garmin USB)
  • Specify the new filename and new layer name. This is where I got stuck for ages! If there is a space in the file name or path name, you’ll get an error message ? This isn’t documented anywhere. So, avoid the desktop, my documents, etc, and check the full path has no spaces.
  • Finally click OK. And hope for the best!

How tropical is the world?

“Rivers are the major conduits for the transfer of water, particulates and dissolved material from the land to the ocean and more than 50% of this flux enters the global ocean in the tropics” (*)

This sentence made me wonder, incidentally, what proportion of the world’s surface area is contained between the two tropics. A friend pointed me to two websites that answer the question.

First, someone who had wondered just the same thing:

And a list of formulae relating to spheres:

The answer is surprisingly simple: the surface area of a sphere (radius ‘r’) that lies in between two parallel planes (‘h’ apart) = 2*pi*r*h !!

In the case of the tropics, h = 2*sin(23.5)*r … so the answer to the tropical surface area is approx. 0.398, or 39.8%, or about two fifths.

Next step (for the GIS) is to calculate the proportion of the land surface area that is tropical…

(*) PETER J HEDLEY, MICHAEL I BIRD, RUTH A J ROBINSON. (2010) Evolution of the Irrawaddy delta region since 1850. Geographical Journal 176:2, 138-149

Using OS MasterMap in ArcGIS

Quick links for reference:

Regarding different transformation methods between OSGB1936 and WGS1984:

For conversion of MasterMap GML to various formats, including shapefiles, using InterpOSe:

Incidentally, a pretty useful description of transformations:

Links from Edina Digimap:

What happened to Uganda’s survey trig. points?

An interesting, if unfortunate, story of what happened to the pillars that constituted (and in a few cases, still constitute)  Uganda’s primary triangulation network:

BTW: this shows a trig pillar atop Malundwe hill in Mikumi Game Reserve, Tanzania (August 2005) – being use as a handy table by a biological survey team:

And the corresponding area on the 1:50,000 topo map sheet:

Fuel wood in Darfur

After a request for possible sources of high resolution satellite imagery to help with a planned fuel wood and landcover study in Darfur, I suggested contacting UNOCHA and UNMIS / UNAMID in Khartoum. This went with some provisos about the difficulty in detecting vegetation, spectrally, that is both sparse and tends to be light coloured, against a background of sand, soil and rock that also tends to be light coloured. As it happened, a few minutes later, I came across this paper, Developing a MODIS-based index to discriminate dead fuel from photosynthetic vegetation and soil background in the Asian steppe area. Although MODIS is coarse in its spatial resolution (250 metres), it is free, frequent (daily), and rapidly available. Indeed, its low resolution makes it suitable for studies of large areas. However, I am doubtful as to how accurate any vegetation detection will be, considering the ‘mixture’ within each pixel.

Nepalese National Grid?

These are notes on a hunt for parameters for the Nepali national mapping grid, after a colleague noticed a mismatch between large scale GIS data, which used an imprecisely defined coordinate system, and handheld GPS positions. Even allowing for a GPS error of say +/- 10 metres, there was still a discrepancy of several hundred metres.

ArcGIS doesn’t have Nepal among its list of pre-defined coord systems (nor incidentally does GPS Utility), so a UN agency in Nepal had gone about defining its own (see ‘1’ below). In effect, this is “UTM Zone 45½”. However, using this, the GPS mismatch appeared. Note that this PRJ definition uses the Everest 1830 ellipsoid.

NGA lists details of the datum used in Nepal here – this refers to the Everest 1956 ellipsoid.

NGA further lists the various Everest ellipsoid parameters here.


Brunei & E. Malasia (Sabah & Sarawak)





India 1830





India 1956*










W. Malasia and Singapore 1948





W. Malasia 1969*





Without some control data, I can’t readily check whether this ellipsoid difference accounts for the observed offset – that will be the next task.

Also, note that the scale factor in the modified PRJ file below is 0.09999, rather than UTM’s usual 0.9996; I’m not sure how much of an effect this would have “on the ground” (is there a graph somewhere of scale error against distance form central meridian?).

In the meantime, I came across a couple of other passing references to similar problems (Evaluating Land Use Dynamics and Forest Cover Change in Nepal’s Bara District (1973–2003) and Mapping cryptic invaders and invasibility of tropical forest ecosystems).

It’s also worth noting the Nepalese Journal on Geo-informatics

From a MapAction perspective, issues 5 and 7 may of of special interest, with various disaster management and hazard mapping articles.


MapInfo rasters to GeoTIFF

A tiny piece of Polish software came to the rescue. At MapAction, we had a request yesterday from our field team in Papua New Guinea for help with converting TIFF files whose georegistration parameters are saved MapInfo format (.TAB file) to something compatible with ArcGIS.

It’s not a complicated task: TAB files are easy to read, and all that’s needed is to calculate the relevant parameters for a TFW file to accompany the TIFF.

The field team doesn’t have MapInfo installed, so a solution needing MI is out. Ideally, we wanted a free solution, ruling out the excellent Global Mapper, for example. Any download had to be as small as possible thanks to limited internet access. And finally, although the team has ArcEditor, they don’t have a license for Data Interoperability Extension, so that wasn’t an option.

After quite a lot of searching, I was pleased to find this neat and effective utility:

It does the job, and best of all, it’s “postcardware” – I hope a postcard will be arriving in Gdansk from Papua New Guinea soon (depending on the post).

Eateries in Cambridge (UK)

There’s some good eating out to be done in Cambridge – if you avoid the town centre (mostly) and avoid the high end – guidelines which probably apply in most cities.

The places I’d choose and recommend are not gourmet temples, and most are quite low key, but all are small and and independent, and have a good mixture of decent food and drink, friendliness, unpretentious decor, and a commitment to what they do. In no order at all:

Efe’s and Meze, respectively on King Street and Mill Road, two roads worth visiting themselves for their variety of shops, for quick, friendly Turkish food.

The Black Cat Cafe, another Mill road stop, with undoubtedly the best cakes in Cambridge, also worth visiting for soup, scrambled egg, smoothies and coffee; the perfect place to pass time on a dull day.

The Rainbow Cafe, the first exception to the avoid-city-centre: this one is slap opposite King’s College, but buried in a basement and far from mainstream in its all-vegetarian meals.

Indigo’s is the another exception, coffee and bagels right behind King’s Parade, and one of the only places to feel part of the jumble of old buildings of the medieval city behind the grander facades. Also one of the smallest and cosiest, just a few tables over two floors and precarious staircase, with orders being shouted down to a basement kitchen.

The final city-centre stop is, flagrantly breaking the no-chains rule, Marks & Spencer’s 2nd floor cafe, for the sole reason of having the best (and only) architectural view of them all – west-facing, so particularly good when the sun is setting over King’s College Chapel.

Back to Mill Road again, the ever-welcoming Kym Moy serves various fast, fresh noodle and rice dishes, with a £5 lunchtime special

Not far along is the Cafe Adriatic, run by Croatians and serving my favorite Italian style food in Cambridge.

Cazimir, after a dip and a temporary name change, is back with a Hungarian theme, notably the soup, and still a good place near the city centre to escape for a meal, coffee and cake.

Further along King Street, go to Clowns for a great Italian welcome, and fresh, ready-made, filling (if not gourmet) food.

The Polish Club is somewhat out of the way but worth the trip  for down to earth, well cooked Polish food and a good selection of beer and vodka.

The Free Press and the Kingston Arms are the places to go for the right mix proper pub and decent food; no gastro-pub makeovers here.

The best food on the list, and somewhat more expensive but well worth it, is at Cotto. On the decidedly un-pretty East Road, and the ideal antidote to the over-priced tourist trap eatery, it is best approached from the west along Elm Street and Prospect Row.

Finally, for the best cup of coffee, everyone agrees Savino’s is the place, always busy and bustling, next to the bus station.

Maps of Central Asia

Also, look at the huge collection of scanned and georeferenced Soviet / Russian topo maps provided at MapStor, and the same free (but less conveniently) at Poehali.