Info on GPS

[guest]

Has anyone got anyfeedback on Etrex Summit GPS systems? Or GPS 76S? Before I lay out the cash any comments or suggestions about weaknesses/new models would be appreciated. Oh yeah, main use is to "lock-in" my favoutite crayfishing holes and track wingsuit flights. Thanks

[BASE_689]

I own and operate an eTrex Vista (which has the same features as eTrex Summit (GPS+digital compass+pressure altimeter) + 24 MB for cartography to be downloaded from PC).
I would say that eTrex Vista is very small, quite robust, you can use it applied onto your helmet to log data about your flights, tracks, etc (and download data into your PC). Also extremely useful for bookmarking exit points and similar stuff. With CD rom's you can get all the world into your eTrex Vista (in 24 MB bits per time!), so you have your exit point exactly on the actual map of the place. For US only, you can have on CD rom's also the topographic map (otherwise, for the rest of the world you can have roads and street level details for main cities). Small display but very, very accurate and high definition. Lots of functions indeed (navigation, moving map, goto, distance-to-destination, etc), and the software is continuously updated (=download from Garmin site and transfer via cable from PC onto GPS). It's got internal light so it can be operated even in complete darkness. Only downside is that it "eats" batteries, but I bypassed that using rechargeable NiMH batteries. Very useful also when you use it in your "private" life, doing trips with your car, looking for accomodation and/or restaurant (=address+telephone number) in a new place/town, etc.
Stay safe out there
Blue Skies and Soft Walls
BASE #689 :D

[obi]

Hi 689!

I thought about getting a GPS for marking extits and measuring flight performance, but also for mountainbiking, ski-touring, car-navigation and and and.
How does that work with the maps? You say that in Europe you've got roads and street level details for main cities. What about maps of mother nature? And if there is no downloadable map, but you've got a old-fashioned paper-map and want to save a route you've planned on your map with waypoints into your etrex, what do you need?
Regarding the measuring of flight performance:
I heard once that some cheaper gps units are too inaccurate when moving at high speeds, such as free fall, cause the intervalls of position calculation are too big. Do you know anything about that? When you set your etrex on auto-mark waypoints, what is the shortest intervall you can use? Is it ok for tracking the flight-path of a 10 sec freefall?
Thanx, Obi

[crwper]

Garmin units will allow you to upload and download tracks and waypoints freely, but Garmin is very tight with their map formats, so if you want a picture in the background, you're S.O.L.

I believe Garmin units (like most GPS units) record position once a second.

I don't really know what the limiting factor is that has led Garmin to record once a second, but it seems like lots of people have had success taking measurements in freefall -- so I assume it works. Anyone out there know enough about GPS to say why these units only record once a second? This is something I'd like to be able to change, but I've had very little luck communicating directly with Garmin.

Michael

[guest]

More Questions....

Does any one know enouth about electronics to say if this is possible. What I want to do is take my Summit mount it on my helmat. Disconect the screen ( extend the wires ) and mount the screen on the inside of my visor, as a head up display. My reasioning is that the summit will give me a constant read out of vertical speed. I believe knowing you vertical speed at all times on a wing suit ( any jump ) would be very usefull.

Greeny

[BASE_689]

Hi Obi,
>What about maps of mother nature? And if there is no downloadable ....
As I said, and as far as I know, apart from US topographic maps, Garmin has NOT got any topographic map of the rest of the world. For the rest of the world, they have only got cities, roads, streets, lakes, main rivers but NOT mountains, altitude contours, trails and so.

>but you've got a old-fashioned paper-map and want to save a route you've planned on your map with waypoints into your etrex, what do you need?
You need to calculate/evaluate lat/long coordinates for each waypoint you like for your route from your paper maps and then create this waypoints into your eTrex inputing coordinate data by hand. Then, on your eTrex you will see your route (=succession of waypoints) on a "blank" piece of map ("blank" if you are moving on a track or mountain or so), but you can still navigate the route, from waypoint to waypoint.

>Regarding the measuring of flight performance: I heard once that some cheaper gps units are too inaccurate when moving at high speeds, such as free fall, cause the intervalls of position calculation are too big... ...Is it ok for tracking the flight-path of a 10 sec freefall?
Yes, as an overall collection of data, for a freefall of 10 s it works, but don't expect to have accurate data for each individual second of freefall. What you can see is the opening point, but please, do not expect that the coordinates of that opening point are "perfect". You can calcualte/extrapolate the efficiency of your freefall tracking, but only for a long freefall (=skydive or very very long delay on a terminal wall), but, again, as an average of the whole set of data, don't take any single point coordinates as "absolutely true". For the flight under canopy, provided it lasts at least 30 s or so, you can get a good average of your canopy efficiency, but, again, the "average" is good, not each single value (the single values appear to be a little bit "dancing").

For my friend crwper-Michael:
> I don't really know what the limiting factor is that has led Garmin to record once a second...
Because the acquisition rate of once a second is WAY enough for the 99.99% of the users for which the portable CIVILIAN GPS units have been thought and designed (mountain hikers, bikers, car drivers, skiers, etc). We are a really small fringe of people who would feel the need of having an acquisition rate of something like 10 times per second. I don't think Garmin is going to modify their software (perhaps also hardware?!?!?) for us, skydivers/BASE jumpers... ...even if to ask to Garmin to have such a modification it is not sin!!!!!!
And, moreover, I do not really know if the 1 s rate of acquisition is a physical limit (on purpose for civilian usage) of the hardware components/circuits by which the CIVILIAN GPS is manufactured (the main electonic component responsible for dialoguing/collecting data from GPS satellites is made by one or two world IC manufacturers and CANNOT be customized...).
Even if, in latest SW version for eTrex Vista (2.31 of 27-sep-02), in the Accessories, they introduced the "Jumpmaster", conceived for skydivers (HALO - HAHO), but, not having the instructions (!!!), it is hard to understand how you must personalize the "parameters" shown...

Stay safe out there
Blue Skies and Soft Walls
BASE #689

[BASE_689]

> My reasoning is that the summit will give me a constant read out of vertical speed. I believe knowing you vertical speed at all times on a wing suit ( any jump ) would be very usefull.

Don't do it, don't do it, don't do it. Even if you could have the display of GPS onto your helmet screen, with such high speeds involved, you wouldn't get correct "in-real-time" results, so what you would be reading at each second of your freefall would NOT be accurate.
For sure, forget about doing that on a wingsuit BASE jump.
Perhaps it could have a very small sense on a wingsuit skydive (where you hang around in air for a couple of minutes), but, again, seen the high speeds involved, at each second of freefall you would not read the actual value of speed (vertical or horizontal that would be), so any action you would take (to modify your pitch according to reading) would be based on a "non-accurate" value of speed. Perhaps, if you have stabilized you rate, after few seconds you WOULD be able to read something that approaches quite well to actual value of speed, but, again, for any action taken you would see the results only seconds later: not very useful indeed... That's not what CIVILIAN GPS have been made for: real time speed readings while moving at high speeds (54 m/s - 194 km/h - 120 mph).
Very precise and very accurate speed readings are obtained, yes, but when you drive your car at a CONSTANT speed (and in a two-dimensional environment: you don't change altitude driving your car, you move only on a plan). When you increase or decrease speed, it takes seconds for GPS to adjust to the actual new value of speed. Do a test while driving your car to verify this.
To complicate more things in our case, is the fact that any action taken in freefall modifies two speeds, horizontal and vertical, and moreover you are moving in three-dimensional environment, making speed readings more "dancing".
Just my 0.02€.

Stay safe out there
Blue Skies and Soft Walls
BASE #689 :D

[Craig]

>Even if, in latest SW version for eTrex Vista
>(2.31 of 27-sep-02), in the Accessories, they
>introduced the "Jumpmaster", conceived for
>skydivers (HALO - HAHO), but, not having the
>instructions (!!!), it is hard to understand how
>you must personalize the "parameters" shown...


http://www.garmin.com/manuals/236.pdf