GPS doesn't love me

Sep 26, 2005 / 0 comments

I finally got the loan of quinophex's Magellan 315. So I went on a wander with it, to see how it faired. (The advantage of a handheld device is that it's self contained, so I can go for a walk with it easily rather than having to bring the USB device and a laptop with me.) However I'm still getting the same offsets compared to the Landsat pictures when I compare on OSM or osm-editor locally. I've set my datum to WGS84, which I understand is the default for GPS. I've made sure the GPS can see a reasonable number of satellites (5 locks is good, right? With an extra couple of marginals?). I was walking, so it's not at any great speed. And yet, as with my USB device, the track is slightly down and to the left.

I'm planning on going on a drive with both devices hooked up to the laptop so I can compare the data from each at the same point in time, but does anyone have any idea why I might be having these problems? Take a look at a screenshot of osm-editor (579KB, 1280x1024) to see what I mean; the track at the bottom is clearly shifted downwards from where the dark line of the road is.

Northern Ireland

Sep 21, 2005 / 0 comments

The English don't really seem to understand Northern Ireland (maybe the rest of the world doesn't either, but I don't get exposed to them as much). I was born in Northern Ireland and lived there until I went to university in England. I still go back there several times a year as my family live there.

The first indication I remember that something was wrong was when I tried to buy car insurance for the first time. I was living in England (car insurance in Northern Ireland is more expensive, and most of the online options won't cover it; I understand this is because injury claims are [or possibly used to be] awarded by jury there, as opposed to by a judge on the mainland. Juries apparently are likely to award more.), and when I was asked if I'd lived in the UK all my life I said yes. Except they knew about me being from Northern Ireland or something (I'd probably asked about being covered for driving back there) and claimed that it wasn't part of the UK. And when I said that yes it was they fell back to "but it hasn't always been". Er, yes, it has. For as long as Northern Ireland has existed as an entity distinct from the rest of Ireland it's been part of the UK. And it's been part of the UK since 1801 anyway. Long before I was born thankyouverymuch.

Since then there have been minor incidents; for example the Post Office clerk not being sure if it cost more to send things to Northern Ireland (she got corrected by one of her coworkers though, and I know that sometimes they won't guarantee delivery times so I forgive her that).

Today I get asked by a friend if Northern Ireland is part of the UK phone network. WTF? Yes. It is. It's part of the UK. No, really. I'll say that again so it sinks in. Northern Ireland is part of the UK. BT are the monopoly telephone provider there. 3, O2, Orange, T-Mobile and Vodafone all provide service there. You don't need a magically different mobile phone contract (the person in question was particularly interested in short codes) if you live in NI rather than mainland UK. Gah. What are these people taught?

(I didn't confuse the issue when explaining to my friend about NI being part of the UK by saying that some call charges do differ; last I investigated ringing Ireland from Northern Ireland with a BT line was the same price as ringing the rest of the UK. Equally it was cheaper to ring NI from Ireland than to ring the rest of the UK. My information is several years old now as I tend to just use my mobile when I'm back there. There's also the oddity about dual citizenship; anyone born in NI has the right to Irish citizenship as well if the choose. Oh, and while I'm ranting, why is the adjective for someone from the UK "British"? Britain doesn't cover all of the UK. I wasn't born in Britain yet I'm British. Can't I be UKish or something?)

A solution for Debian mirroring?

Sep 20, 2005 / 0 comments

Recently security.debian.org has been having some problems with maxing out its connection due to an X update. This reminded me of a conversation I had at DebConf5 about the feasibility of a Debian anycast instance. This was originally under the guise of ftp.debian.org, but there's no reason it wouldn't work nicely for security.debian.org as well.

The idea is that Debian would obtain a /24 of PI (or something unlikely to get filtered anyway; I think anything smaller wouldn't work) and their own AS. They'd then host instances of f.d.o/s.d.o around the world with ISPs that would route this AS for them. This would mean that big sponsors able to provide global routes would still be able to do so, but smaller sponsors (like Black Cat) would still be able to help out by announcing the route to their peers.

You'd need the servers involved to all be reliable push mirrors, so that they're as close to being in sync as possible. And I'm not sure how well TCP works over anycast; assuming stable routing I can't see why it'd be a problem (does the Akamai service work this way?). Certainly it seems to be quite common for major DNS servers these days. But it could end up with quite a few decent local mirrors with no work required on the part of the users to take advantage of them. Am I insane?

Mapping the world for free

Sep 18, 2005 / 0 comments

I had a conversation a few weeks ago with Tristam and some other people about direction finding in terms of car navigation systems, and how I felt it reduced to a weighted directed graph and that it should be possible to build from a large enough set of GPS logs. There was general agreement that this wasn't unreasonable. This prompted me to actually see what was out there, which led me to OpenStreetMap, who have been going for over a year now and see to have a reasonable number of people involved.

They lack any data around Norwich however, so I thought I'd see what I could do to remedy that. I bought a basic USB GPS device, hooked it up to my laptop, installed gpsd and gpsdrive and went for a test drive. gpsdrive seemed to be doing the right thing, with the track it drew matching up with the map being displayed. However when I uploaded it to OSM it seems to be out by a reasonably constant factor. This has led me into the tricky world of GPS datums and hoping that that's what at fault rather than it being the fact I bought a cheap Haicom Hi-202 rather than something more expensive. quinophex has a Garmin however, so he's going to lend it to me so I can run the 2 side by side and see what happens. It'd be really nice if I discovered it's just a conversion thing and that the tracks I got of a trip to and from Redbus could still be imported...

Anyway, if you do GPS stuff at all I'd highly recommend uploading some tracks of your local area and even potentially doing some markup of nodes and streets; if everybody just did a little bit local to them and perhaps a few longer journeys then things should start to get linked up and filled out, which would increase the appeal a lot.

Useful v600i BlueTooth tips.

Sep 7, 2005 / 0 comments

I suspect these apply to lots of Sony Ericsson phones, but I know they definitely work with my v600i and I couldn't find them anywhere all together.

  • Asking the phone for a non existent file via obexftp makes it very unhappy; apparently often to the point where the phone needs turned off and on again. This is bad.
  • ussp-push is your friend.
  • To send a vCard (or many in one file) to the phone, do: ussp-push <BT ADDRESS>@5 <local vcard file> pb.vcf. The phone will recognise the "pb.vcf" (in particular the .vcf extension I believe) and ask if you want to import the contacts.
  • To send a Java App (ie a .jar file) do: ussp-push <BT ADDRESS>@5 <app.jar> <app.jar>. Again the phone will recognise the extension and then ask where you want to save it - under Games or Applications.
  • The normal AT dialup/GPRS command set works fine on rfcomm channel 1.

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