Comments on: Stereoscopic GPS

By: fekaylius

fekaylius — Wed, 19 May 2010 02:43:31 +0000

following you on twitter now, look forward to seeing more work!

By: nikki pugh

nikki pugh — Wed, 19 May 2010 02:37:03 +0000

"maybe those GPS traces aren't in the wrong places, but are in the wrong times"

Oooh! Yes! That's a brilliant way of describing it!
On a micro scale, I think the signal reflects off large buildings and that tiny, tiny extra fraction of time shifts the calculated position.
On a macro scale... Wow! It's a fascinating idea!

The extruded lines on the image from Google Earth were just given arbitrary heights. I've not tried working with altitude data in mscape (what I'm using to log the positions), but I assume it exists. I'll have to give it a go and see what happens!

By: fekaylius

fekaylius — Mon, 17 May 2010 20:52:44 +0000

oh wow, i didn't see the extruded images till just now, those are really wonderful!
is the extrusion based on altitude data? or just arbitrary for visual effect?
nice either way.

By: fekaylius

fekaylius — Mon, 17 May 2010 20:46:31 +0000

Thanks for the links Nikki,
By temporal drift I mean that GPS is predicated on the notion of perfectly synchronized timestamps, I don't know *exactly* how it works, but my understanding is that the GPS satellites send out a beacon signal that includes a satellite ID and a timestamp of the moment that pulse was sent out. The receiver can deduce distance to the satellite by subtracting the reception time from the transmission time. If the receiver can do this with 3 or more satellites, it works (of course the receiver needs to know the positions of the satellites as well, and I'm not sure if that data comes along inside the transmission, or if it's looked up). The distance calculations are based on known and stable velocity of the transmission in a straight line, but if anything interferes with this transmission (not sure if this is even possible) that could delay or alter the known values, the whole equation suffers. Specifically I'm thinking about perhaps variances in the magnetic field around the earth, or interference with other kinds of transmissions, or solar flares, etc. I'm not a physicist, so these questions may just be off base. But the core of my question is something like, maybe those GPS traces aren't in the wrong places, but are in the wrong times.

By: nikki pugh

nikki pugh — Sun, 16 May 2010 03:32:33 +0000

Here's a photo of the traces from the 3 walks I did for Territorial Play: http://www.flickr.com/photos/nikki_pugh/4609506... (one at 9.30 am, one at 12pm and one at 2pm) It's unlikely that time is the only factor to have changed, but I'm walking the same route to within a metre each time and holding the machines in the same hand each time I walk. Is this what you mean by spatial drift? (Doesn't all drift have to be temporal!?). Each line, however, is representative of a moment in time, so the drawings can only show drift at certain levels…

The overhead positions of the GPS satellites changes with time, so it's natural for signals to change. Also, my experience with GPS devices is that they're kind of jittery on a much shorter timescale too: http://www.flickr.com/photos/nikki_pugh/3300090...

I like the 3D walkthrough idea. The closest I've come so far is this sort of thing in Google Earth: http://www.flickr.com/photos/nikki_pugh/3919609...

By: LO

LO — Sat, 15 May 2010 17:35:22 +0000

INVIGILATOR:MALVERN
Splacist Trace Print http://post.ly/g6Fh Nikki Pugh

From: Invigilator:Malvern Conneally & Pugh 2009