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 Going up stairs with GPS - position frozen ?
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mich_blogs

6 Posts

Posted - 02 févr. 2012 :  05:44:50  Show Profile  Reply with Quote
I recently got a GPS module to add to my robot, and since I am not very familiar with GPS I have hooked it up to my computer and I have been experimenting.

I've noticed some really strange behaviour when I walk up and down stairs carrying the GPS.

While I am waiting for the train, I walk up and down along the station platform, carrying the laptop computer with the GPS. I am particularly interested in how quickly the GPS notices that I have started walking from a stationary position. What I find is that it normally notices I have started walking after ten paces.

The strange thing I have found, is that the GPS does not work when I walk up the stairs to the overhead footbridge across the tracks. There is no canopy or other obstruction to the view of the sky on the stairs or the footbridge. As soon as I start walking up, or down, the stairs, the position reported does not change. If I continue to walk along the footbridge and along the street ( after going up the stairs ), or along the platform ( after going down the stairs ), it eventually starts responding with changing position updates after I have gone 50 or 100 metres. It often repeats exactly the same position for up to three minutes, although I am still walking.

This phenomenon can be repeated multiple times walking up and down different flights of stairs. On multiple days. On multiple train stations. Its very strange !

My first thought, is that my apparent horizontal speed going up stairs is less than normal walking speed (4-5 km/hr ), therefore the GPS thinks I must be not moving at all.

My second thought is that it is somehow confused by the combination of vertical and horizontal movement.

Has anyone come across such a phenomenon before ? Any suggestions ?

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frder

Italy
46 Posts

Posted - 02 févr. 2012 :  15:07:36  Show Profile  Reply with Quote
"My first thought, is that my apparent horizontal speed going up stairs is less than normal walking speed (4-5 km/hr ), therefore the GPS thinks I must be not moving at all."

You are right. It's a filter called "Static Navigation", to prevent change in position due to multipath.

You need to get a gps module that does'nt apply Static Navigation.

"My second thought is that it is somehow confused by the combination of vertical and horizontal movement."

It's not a matter of confusion. Gps position and speed always refer to the horizontal plan.
If you climb a wall the position does'nt change and the speed reported is "0".

francesco


Edited by - frder on 02 févr. 2012 17:10:05
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mich_blogs

6 Posts

Posted - 03 févr. 2012 :  10:36:35  Show Profile  Reply with Quote
"Gps position and speed always refer to the horizontal plan.
If you climb a wall the position does'nt change and the speed reported is "0"."

Thats quite right. But when I am walking around doing these tests, the GPS usually notices I have started walking after I have gone about 8 metres.

But if I walk up stairs , it "locks up" its position and doesn't resume reporting until I have gone 20-100 metres after I walk up the stairs.

These are not very big stairs. Its not a ladder or anything. It goes up less than 5 metres at a small gradient.

I've tried stopping before the stairs, I've tried approaching the stairs from some distance away and walking right up them, I've tried running up the stairs, I've tried stopping halfway up the stairs.

I think you are right about this "static navigation". The GPS chip works ridiculously well when I am actually on the train, even though it has a poor "view" out of the window. But when walking around, its quite poor. I'll look into that some more.
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trah

Canada
7 Posts

Posted - 04 févr. 2012 :  17:41:31  Show Profile  Reply with Quote
What GPS chipset are you using?

Also what about your laptop settings? My laptop often stops the hardrive when it senses accelerations to prevent damage. Could it be that the acceleration limits aren't reached when walking but going up stairs it is more difficult to keep the laptop steady?

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mich_blogs

6 Posts

Posted - 15 févr. 2012 :  05:24:00  Show Profile  Reply with Quote
The chip is labelled GTPA010 and I believe it has a 3329 chip.

The laptop is fine walking up and down the stairs.

I have done more experiments with this. It works fine if I run up and down the stairs. The GPS seems to report
zero movement if I walk less than 4 km/hr, on stairs or anywhere else.

When I walk faster than 4 km/hr, it works OK. On stairs, by their nature, it is hard to achieve
4 km/hr horizontal velocity.

I don't really mind that when I walk up stairs at a normal speed, it doesn't report the position change.
Thats not the problem. The problem is that it then seems to retain the locked position for up to 200 metres
additional walking. This problem seems to occur uniquely where stairs are involved. If I just normally stop
walking, and then start again, it invariably starts reporting movement again after I have gone only 8 metres.
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gpspassion

93993 Posts

Posted - 25 avr. 2012 :  22:58:58  Show Profile  Visit gpspassion's Homepage  Reply with Quote
Interesting, does look like a bug with a filter, it's an MTK v2 chip apparently. Did you ever get to the bottom of this?

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