Recommended Posts
veter_ 0
For consumer GPS's, with their accuracy 3-10ft, data recorded in such small intervals will be too "noisy".
KrisFlyZ 0
QuoteFor consumer GPS's, with their accuracy 3-10ft, data recorded in such small intervals will be too "noisy".
Yup, I used to have the logger set at 1 sec. The best number I have seen on the screen as far as accuracy goes is 7 ft. If logging at 1 sec intervals, a 1 sec interval will yield an error of atleast 14 ft(for 1 sec = 14fps) error or for 100 fps(68 mph) total speed the error is 14 percent or higher.That is too high.
The same numbers if logged at 3 secs yield an error of 4.4 percent or higher.
Kris.
vidiot 0
Kris,
Based on my experience, the spatial resolution and accuracy does not directly impact speed accuracy. Although your absolute position might not be accurate, two consecutive positions are usually quite accurate compared to each other, i.e. the position does not 'jump'.
You can verify this with this simple experiment: Switch on your GPS receiver and stand still. Although your unit might report an accuracy of 'only' 7ft, your measured and displayed speed will usually be zero.
This chart demonstrates what I mean.
Klaus
Based on my experience, the spatial resolution and accuracy does not directly impact speed accuracy. Although your absolute position might not be accurate, two consecutive positions are usually quite accurate compared to each other, i.e. the position does not 'jump'.
You can verify this with this simple experiment: Switch on your GPS receiver and stand still. Although your unit might report an accuracy of 'only' 7ft, your measured and displayed speed will usually be zero.
This chart demonstrates what I mean.
Klaus
My Logbook
Han-Solo 0
maybe not the quickest there is, but i've used one logging at 5 hz. the accuracy was amazing. though i never had anything to compare the actual accuracy to, as mentioned, what you want is relative accuracy. it has only bee used for basejumping, but small variations in flying performance were very noticeable. opening characteristics too. also movement on the exit down to half a meter is very noticeable. but it wasn't made for jumping or any other sporting activity, and was very bulky and impractical. i have been looking for a gps that logs quick, but 1 hz is the quickest i've seen around.
i don't believe increased logging speed will make it more inaccurate. what it does is it makes it possible to see the errors that occur, and then you are able to manually correct them later if you'd like. for example, if you log at 100 hz and you trace your log suddenly you have ten feet between two points, you can adjust this. but if you log at 1 hz, because your points would typically be 100(ish) feet apart, an offset of ten feet is undetectable.
using this 5 hz logger i've often seen these offsets occuring, in the range of 10-20 feet.
because of the bulky impracticality of the gps i used, i have been looking for something smoother with the same update and logging speed. not having found anything in this range, the project now is to assemble one...
i don't believe increased logging speed will make it more inaccurate. what it does is it makes it possible to see the errors that occur, and then you are able to manually correct them later if you'd like. for example, if you log at 100 hz and you trace your log suddenly you have ten feet between two points, you can adjust this. but if you log at 1 hz, because your points would typically be 100(ish) feet apart, an offset of ten feet is undetectable.
using this 5 hz logger i've often seen these offsets occuring, in the range of 10-20 feet.
because of the bulky impracticality of the gps i used, i have been looking for something smoother with the same update and logging speed. not having found anything in this range, the project now is to assemble one...
Nidez 0
Sorry for the stupid question, i've buyed the foretrex 101 and i've got a problem I really can't track the satellites while i'm in the aircraft !
If i turn it on while standing on the ground it align correctly with the sats, i wait one or two takeoff (40 mins) and then when i board for my load the foretrex can't "listen" for sats anymore... I tried to give it to the pilot who putted on the copickt i've tried in a Turbo Finist and in a PC-6 Pilatus too, same problem...
When i exit from the plane it took too much time to re-align with sat (5 mins) and so...
This can't be the right way, do you have any suggestion ?
If i turn it on while standing on the ground it align correctly with the sats, i wait one or two takeoff (40 mins) and then when i board for my load the foretrex can't "listen" for sats anymore... I tried to give it to the pilot who putted on the copickt i've tried in a Turbo Finist and in a PC-6 Pilatus too, same problem...
When i exit from the plane it took too much time to re-align with sat (5 mins) and so...
This can't be the right way, do you have any suggestion ?
Marco "Pazzo" Pistolesi
pistolesi.marco(at)gmail.com
pistolesi.marco(at)gmail.com
vidiot 0
Marco,
this is not a stupid question at all! Although I have no personel experience with a Porter or Finist, I have succesfully used the ForeTrex 101 through the windows of other planes and cars.
Actually, the big front window of the Porter should be ideal as it gives you a clear view of more than half of the sky. I can think of two possible reasons creating the problems: The windshield might be metal-covered as insome cars or the built-in GPS or some other on-board electronis create interference.
What happens if you try to get a satelite fix through the front window on the ground with all electronics switched off? Would a re-radiating antenna be an option?
Does anybody else have some good or bad experience or background information on using GPS in a Porter?
Klaus
this is not a stupid question at all! Although I have no personel experience with a Porter or Finist, I have succesfully used the ForeTrex 101 through the windows of other planes and cars.
Actually, the big front window of the Porter should be ideal as it gives you a clear view of more than half of the sky. I can think of two possible reasons creating the problems: The windshield might be metal-covered as insome cars or the built-in GPS or some other on-board electronis create interference.
What happens if you try to get a satelite fix through the front window on the ground with all electronics switched off? Would a re-radiating antenna be an option?
Does anybody else have some good or bad experience or background information on using GPS in a Porter?
Klaus
My Logbook
Nidez 0
putting the gps under the front window let it acquires some sats, but when we are 1 min to go (red light) i have to start prepare myself and.... zip, helmet, gloves, eye, camera, gps, checks... ok, "exit exit"... first RW4 (10 sec), 2 people in Freefly (6 sec) and last an AFF (15 sec) it's my turn... but in this little period of time the sats are all lost...
Marco "Pazzo" Pistolesi
pistolesi.marco(at)gmail.com
pistolesi.marco(at)gmail.com
Mount the unit on top of your helmut, sit in co-pilot seat of the porter, turn on GPS 5 minutes before exit and stay in the seat until your turn to exit - works for me 
Cieli blu
J
Cieli blu
J
BASEstore.it
vidiot 0
Glad to hear this. So it's not the Porter or it's windshield! It is an unfortunate fact that GPS signals can not be received in buildings, forests(!), cars and planes without a clear view to a larger part of the sky.
Nevertheless - without going into the technical details - short interruptions of satelite reception should result in a 'hot fix' with a re-aquisition time of less than 15 secs.
What can you do to improve the situation? Keep a satelite fix as long as possible, be quick getting to the door, get a new fix while waiting in the door. When jumping a Porter, can't you just do a diving exit directly from the co-pilots seat out of the door? This should keep the interuption to a minimum. ;-)
HTH,
Klaus
Nevertheless - without going into the technical details - short interruptions of satelite reception should result in a 'hot fix' with a re-aquisition time of less than 15 secs.
What can you do to improve the situation? Keep a satelite fix as long as possible, be quick getting to the door, get a new fix while waiting in the door. When jumping a Porter, can't you just do a diving exit directly from the co-pilots seat out of the door? This should keep the interuption to a minimum. ;-)
HTH,
Klaus
My Logbook
Nidez 0
Tnx to all 4 helping.
Marco "Pazzo" Pistolesi
pistolesi.marco(at)gmail.com
pistolesi.marco(at)gmail.com
While some vehicles have windshields that prevent GPs signals from being received, I am not aware of any aircraft windshields being that way but it is possible.
However, I don't think that is the root of your problem. The foretrex is a small receiver with an internal antenna and a small power source. All GPS receivers must be able to "see" the satellites in order to get a fix. Some are capable of being out of contact for a few moments and based on the information it received from the almanac when it was receiveing signals, can predict where the satellites "should" be when it is able to see the sky again. I think the problem you're experiencing is one we all encounter when inside an aircraft with a GPS. Depending on what I am doing, I sometimes use the external antenna on my Garmin GPS V and mount it out side with the attached magnet. I have full coverage from ground to altitude that way. Since you do not have an external mount on your receiver your only option is to use a re-radiating antenna so that you maintain GPS signal inside the aircraft. You can find battery powered ones if you look around but most come with the 12 volt cigarette adapter plug. They are not too expensive and they work great for GPS receivers with no external mounts or when working inside an enclosed area.
However, I don't think that is the root of your problem. The foretrex is a small receiver with an internal antenna and a small power source. All GPS receivers must be able to "see" the satellites in order to get a fix. Some are capable of being out of contact for a few moments and based on the information it received from the almanac when it was receiveing signals, can predict where the satellites "should" be when it is able to see the sky again. I think the problem you're experiencing is one we all encounter when inside an aircraft with a GPS. Depending on what I am doing, I sometimes use the external antenna on my Garmin GPS V and mount it out side with the attached magnet. I have full coverage from ground to altitude that way. Since you do not have an external mount on your receiver your only option is to use a re-radiating antenna so that you maintain GPS signal inside the aircraft. You can find battery powered ones if you look around but most come with the 12 volt cigarette adapter plug. They are not too expensive and they work great for GPS receivers with no external mounts or when working inside an enclosed area.
"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING
veter_ 0
Another question:
if you mount GPS on your chest, does it see satellites? Did anyone try to mount Etrex Vista on your chest and see the altitude vs. distance plot in real time?
if you mount GPS on your chest, does it see satellites? Did anyone try to mount Etrex Vista on your chest and see the altitude vs. distance plot in real time?
Quoteif you mount GPS on your chest, does it see satellites? Did anyone try to mount Etrex Vista on your chest and see the altitude vs. distance plot in real time?
I wear my Vista on my chest strap and it still picks up satellites. I make sure to stand outside the aircraft(otter) after the last skydiver exits so I can reaquire sats before I exit. Ocassionaly, I will loose a bit of data on the top end but overall, I still get the meat of the flight.
"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING
veter_ 0
Thanks, Lou. How do you mount Vista on your chest strap?
QuoteThanks, Lou. How do you mount Vista on your chest strap?
I use one of the aftermarket cases made out of neoprene for use on the water. It has a clear piece of plastic so you can see the face and it closes with a pretty strong piece of velcro on the 1 flap. The back of it has a sewn belt style loop that I route my chest strap through.
"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING
veter_ 0
Where can I buy such a case? (My shopping skills suck
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING
Share this post
Link to post
Share on other sites