Numpty's Progress

probably wouldn’t recommend the Blackberry Tour as a GPS logger

scruss — Sun, 22 Aug 2010 02:10:36 +0000

I walked a local footpath carrying my (mostly) trusty Garmin GPSMap 60Csx, and a Blackberry Tour running bbTracker. Both had had a good satellite fix for about 10 minutes beforehand, and both were logging trackpoints every second. The smooth turquoise track from the Garmin is much more useful than the wibbly one from the Blackberry.

Taking geotagged pictures with your Blackberry Note: I’ve had reports that some carriers seem to disable...

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fallout from last night’s OSM 6th birthday Mappy Hour in Toronto

scruss — Sat, 21 Aug 2010 13:49:25 +0000

It was fun – there were geo-aware cupcakes!

It is very easy to lose days in the David Rumsey Historical Map Collection.
Richard’s OpenStreetMap for the Beginner tutorials are actually really really good.

In a moment of geek worlds colliding, Emma showed up, and now I have people clamouring for tablet at Mappy Hour. Sigh, those old ecommons links just don’t fade …

in which I discover OpenStreetMap editing While I’ve used OpenStreetMap data before, I’ve never added anything...

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proj.4 init annoyances: it’s all apple’s fault

scruss — Sun, 08 Aug 2010 16:09:21 +0000

I was going to write a rant about how Ubuntu sets up proj.4 init files incorrectly, then I found that the problem actually lies with OS X. OS X is unusual for a Unix variant, as it uses a case-insensitive file system; flarp.txt is the same as FLARP.TXT. Under more traditional Unices, they’d be different files.

Most of the examples on this blog were written under OS X, and I was concerned when they didn’t work under Ubuntu. It seems that proj.4 uses a very simple way of defining initialization files. If you specify, say, “+init=EPSG:2958″, proj digs around in its configuration files for a file called EPSG, then searches for an identifier in that file which matches the ID 2958. Under OS X, you can specify EPSG, epsg, or even EpSg – they all work. Under Ubuntu, using anything other that epsg fails with this message:

:
projection initialization failure
cause: no system list, errno: 2

In short, use lower case init specifications, and it’ll work everywhere.

It seems that there are some other applications (mapserver?) that have problems calling proj, so if you’re seeing this error and it’s not something you can correct from the command line:

Find out where your installation keeps its initialization files. You can do this by setting PROJ_DEBUG=1:
PROJ_DEBUG=1 proj +init=epsg:2958
and you should get a message like:
pj_open_lib(epsg): call fopen(/usr/share/proj/epsg) - succeeded
cd /usr/share/proj (or wherever the last command said the epsg file was located)
sudo ln -s epsg EPSG

Now your installation should work no matter which case you use. Camel case, unfortunately, excluded.

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in which I discover OpenStreetMap editing

scruss — Thu, 29 Jul 2010 01:39:17 +0000

While I’ve used OpenStreetMap data before, I’ve never added anything to it. That changed after going to Mappy Hour last night, and meeting Richard Weait. He has a bunch of useful tutorials on his website.

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toronto data updated

scruss — Fri, 16 Jul 2010 12:04:46 +0000

Hey, they’ve updated most of the data sets on toronto.ca | Open! Related posts:Land Information Ontario – or, how I semi-accidentally ordered 3.5GB of terrain data The Ontario Ministry of Natural Resources has a fairly well-hidden... free geodata for the numpty-about-Toronto So if I want to learn some GIS skills, it... The highest point in Toronto The highest [...] Related posts:

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More on iPhoto GPS weirdness

scruss — Sun, 11 Jul 2010 03:09:09 +0000

Okay, so I geek out a lot here, so here’s a summary: In a test of 1600 images, iPhoto moved the recorded GPS location of a picture an average of 6.17m, and in one case moved the image 11.25m from its correct position.

I created a 40×40 array of points approximately 5m (okay, 5 UTM units apart, precisely) and assigned the locations to JPEG files using ExifTool. These files were imported into iPhoto, then exported. The before and after coordinates were plotted and compared:

The green crosses are the original coordinates
The red crosses are the coordinates assigned by iPhoto
The dashed lines map the before coordinates to the after.

In real life, I realise it’s difficult with most consumer GPS units to resolve points 5m apart. It’s pretty egregious of Apple, however, who appear to take great pains to retain all the camera’s metadata, to mash the stored coordinates so badly.

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My Neighbourhood, Canada Day 2010

scruss — Mon, 05 Jul 2010 02:54:00 +0000

I went for a bike ride on Canada Day. Click on a bicycle icon to see what I saw.

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Don’t trust iPhoto’s exported GPS coordinates

scruss — Sun, 04 Jul 2010 21:52:54 +0000

John the new jersey geographer put this better than me, but it appears that iPhoto rounds exported GPS coordinates to the nearest integer second of arc. There’s really no reason for them to do this, and it’s caused me to waste several hours tracking down why my tagged and exported photos didn’t match up.

Looking at the output data, I’m not sure if it’s to a second of arc – it appears to be rounding to the nearest hundredth minute, or approximately 0.000167°. Since GPS location uncertainty is in the fifth decimal place, this aliasing of the data is annoying.

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The highest point in Toronto

scruss — Mon, 21 Jun 2010 02:08:57 +0000

The highest point in Toronto has an elevation of 211m, and appears to be in the middle of one of York University‘s playing fields, just southwest of Keele & Steeles W:

The red blob is the 211m contour, and the centre point is at 43.779325°N, 79.492655°W. The contour was derived from the MNR DEM data for the province.

The city says the highest point is 209 m (at intersection of Steeles Ave West and Keele St), which is pretty close in all three axes.

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MNR DEM tiles

scruss — Mon, 21 Jun 2010 01:43:12 +0000

So I got the DEM tiles for my zone, couriered from Peterborough. Even zipped, they are several gigabytes. Here’s a visual guide to the tiles I got:

It seems that every project I work on is split across several tiles. My fair city is no exception:

Most of the city is in tile 87, but the northern and eastern corners poke into tiles 91 & 92. Merging the files and pulling out the area isn’t that hard.

First off, we need to know the extents we want. Conveniently, I’d already transformed the Open Toronto data to the same CRS, so I could just go from the extents of one of the city shape files:

$ ogrinfo -al ../open-toronto-shp/dest/2958/city-wards/TCL3_ICITW.shp | grep '^Extent'
Extent: (609538.195527, 4826360.800158) - (651613.577420, 4857439.389359)

You can then use gdal_merge.py to merge the tiles. Annoyingly, rather than using the familiar ‘lower left – upper right’ coordinate convention for bounding box, it uses ‘upper left – lower right’, so working out a buffered bounding box is a bit of a pain:

gdal_merge.py -v -of EHdr -o Toronto.flt -n -9999 -ul_lr 609000 4858000 652000 4826000 `find . -iname 'd*.flt'`

The MNR DEMs are shipped as ESRI .hdr Labelled files, 32-bit floating point. The CRS used is NAD83 Zone 17N. For all that they’re large, they’re quite quick to load and move around.

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