Can GPS devices calculate vertical speed?
April 12th, 2010 | by admin |Can GPS devices calculate vertical speed? I know that GPS devices can calculate horizontal speed (the object’s speed on a horizontal, two dimensional plane). But can they calculate the vertical component of someone’s speed (say, if someone is going downhill) and use both horizontal and vertical components to calculate actual speed? Thanks, Brian
The GPS I’m using calculates speed using position and time. It’s very accurate on flat surfaces (while driving). I know that it thinks in two dimensions, but can it think in three? I read somewhere that if it has reception from two satellites, it can calculate position in 2d. If you have four or more satellites, it can see where you are in the third dimention. Also, some GPS devices have built in topographic maps, that roughly show change in elevation, but if that is the case with mine, then the vertical component isn’t being calculated.
I was skiing backwards down a diamond run at a ski resort, and wanted to know how fast I was going. The gps read 21 mph, but I don’t think that it could tell the vertical velocity. If you think about it, if I’m on a 45 degree slope, and I’m only getting the horizontal velocity, the vertical velocity would be equivalent to that, giving a resultant velocity of around 30 mph. If I go back and measure the angle of the slope, I could calculate the exact speed I was going, but I’m still not sure if the gps was giving me the resultant velocity or only the horizontal velocity. I know that 30 mph sounds like wishful thinking, but I was going pretty damn fast. That, and my forward skiing speed is up to 65 mph, making my backwards skiing 1/3 to 1/2 my normal skiing speed, and both seem likely to me. Thanks for the help, Brian
no they use satelite to only find out maps and your direct location
8 Responses to “Can GPS devices calculate vertical speed?”
By riiman95 on Apr 13, 2010 | Reply
no they use satelite to only find out maps and your direct location
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By caitnop87 on Apr 13, 2010 | Reply
Yes, some of the higher end GPS units can. I’ve got a Garmin Rino 120 at it calculates my current altitude, but doesn’t do rate of vertical speed. Look at some of the Garmins designed for aviation, they should be able to calculate vertical speed.
EDIT: Yup, take a look at the Garmin GPSMAP 76CS. It will tell you ascent/decent rates.
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By Thin Kaboudit on Apr 13, 2010 | Reply
Riiman is mistaken, a GPS device calculates your precise location (within any margin of error) in three-dimensional space, so the data are there to calculate your speed in any plane.
Think about it, if that weren’t the case, how could an aircraft on autopilot using GPS ever land?
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By lynn b on Apr 13, 2010 | Reply
A GPS can determine horizontal locations with a great deal of accuracy through triangulation. We have some units in house that can, after sitting at a single location for an hour, give you the location within 0.01 feet. Vertical is another story. A GPS cannot accurately triangulate on satellites to give you a good vertical component no matter how many satellites it is tracking.
You would have more accuracy from an altimeter. I’ve seen some inexpensive recording units that also record time. A little Excel work on the download and you can get vertical speed.
If you can expand on what you are doing, I might have some idea on how to solve your problem without a GPS.
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By Cultural_Noise on Apr 13, 2010 | Reply
Only if you have a system capable of differential GPS will GPS provide the necessary vertical resolution to provide an answer to your question, or if you have a military grade unti that allows you to decode multiple channels from a single satellite. Without this information, you cannot compensate for the atmospheric effects which play havoc with GPS vertical resolution.
Most commercial systems available for people and cars don’t do this, but the WAAS-enable units will provide a correction that can get you closer to the resolution of a differential system.
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By abadfish on Apr 13, 2010 | Reply
GPS can be used to do vertical velocity. You do not need differential GPS or a military GPS receiver (though it may not be as accurate).
The real question is "does your software on your GPS unit report vertical velocity?????" Most do not and only report horizontal velocity.
Now if you’re willing to do a little extra work, you can do it yourself. All consumer GPS receivers calculate velocity by differencing one position solution (which comes out at 1Hz) to the next. That’s why there is a lag in the velocity reporting on consumer GPS units. You can do the same with the altitude your GPS receiver is reporting. But you’ll need to either record this data [somehow] and either post process it or compute it in real-time. This will likely require a laptop or some other computer for data collection which means you lose your portability.
However, it may not be as accurate as the horizontal velocity because many consumer units round vertical component of the position solution to the nearest foot. This will intoduce a lot of error in your computation.
If you really want a precise (well, as precise as a standalone GPS can give you) vertical velocity, you could process the raw measurements (GPS pseudoranges) on your own (essentially ignoring the position solution your GPS receiver is giving you). But you can only do this if your receiver has the capability to output those.
In either case, vertical computations with GPS has some errors in it, larger than horizontal. Most of this is due to the lack of geometrical contraints due to spatial distribution of the satellites. There also some atmospheric delays (as previously mentioned). Though they are small (adding several meters of delay in pseudorange), they do add inaccuracy.
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I develop GPS receivers.
By nycking5984 on Apr 13, 2010 | Reply
yes they can…..its simple triangulation……tele atlas mapping technology does a very fine job with this, and they are very accurate. I’ve tried it on my mio c220 and i found it to be very precise.
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By gaijin on Apr 13, 2010 | Reply
yes they can
http://gps-mobile-tracking.com/GPS.html
http://gps-mobile-tracking.com/
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