GPS Tips for Pilots

Info for pilots on how the GPS based Turnpoint Verification Software TP works

To be given at briefing to pilots

The program can check

- If pilot took off from designated take-off area and within time window
- If the track log shows a steady time increment and has not been tampered with
- In case a Start of Speed Section is used ,if the pilot has crossed over the Start Circle and within  the time window
- If the pilot went over thee Turnpoints
- If the pilot made it to goal and within goal window time frame
- In case pilot was flying after cut off time, takes last position at cut off time
- if he lands out , calculates the best Track point position to give him the best score
- Interpolates goal crossing and start section crossing time
- Waypoints created at the task date can be checked visually
- Once Pilot has taken off and there is no change in the track coordinates, then the program assumes he has landed
- Checks the speed and highlights if a pilot is below, or above, certain speed limits.
- Can check for going above a predefined ceiling, if the GPS device provides altitude info

Competition Organizers have to decide if a GPS is allowed to be switched off/on in flight.
If the Track records have to be uninterrupted.
Older GPS , like 38 or 40, do not have a big memory and tend to loose the satellites.
eMap and eTrex got a far too high sample rate and also tend to fill up memory fast.
For those GPS one has to allow for having them switched off and on in flight.

Recommended GPS settings are :

- Time Zone settings to local time zone. Example South Africa is +2
- All use the same coordinate format, in Zimbabwe for example UTM, because the maps are based on UTM
- WGS84 coordinate system for South Africa
- Decide on a Track sample rate to avoid memory to fill up
- At each briefing, put in your route and then clear the track log and switch off GPS
- Decide on FILL or WRAP mode.
FILL mode avoids overwriting beginning of track.
If you get to goal, you might loose the end of the flight but the turnpoints are there.
And in case you forget to switch of the GPS or it gets switched on by mistake,
your flight is preserved.
WRAP mode is advisable when you land out and got some turnpoints in between.
Take off might be lost but at least the turnpoints are there and where you landed.

- TP assumes that when you exceed a certain speed (this depends on a setup value) in Take off area is a launch.
eMap and eTrex do not collect track data until you start moving.
And then eMap or eTrex can do it every second.
If you move more than 10 meters on the ground while your GPS is on, clear your track log again.
- Best , switch on you GPS just before you plan to take off
-  Find out if the comp organizers allow marked waypoints.
If allowed , then while in the air, use MARK to log Takeoff, Start tarp, Turnpoints, Goal or Landing Spot.
In case the track log memory is not sufficient, waypoint data could be used.
Or in case you are doing a very tight turn
without spending 15 seconds in sector of a turnpoint.

- Once landed, to be on the safe side , Mark , Enter your position. In case there is a problem later to determine your exact landing.
Then switch off your GPS. Otherwise your track log keeps recording.
The program assumes no movement as landing or the last point of the track log is where you landed.
If your GPS allows to save a track, DON'T. Saving a track reduces the collected track info.

If you have to use your GPS after your flight, switch the track recording off.
But remember and switch on the track recording mode again the next day.

To protect your track log , keep your GPS switched off and leave it off until  the PC operator at scoring tells you to switch it on.
No good to collect track points at the meet center overwriting your start.
If you use a NMEA link to your VARIO, switch the Interface protocol to GARMIN/GARMIN to speed up the track download.
With  NMEA, the download will fail and create some delay in the processing of the downloads.
Hang on to your track log until you are happy with the score. Do not clear your track until the next briefing with a new task was given.

Label your GPS to give it an individual look.
Sometimes there are computer problems and the competition organizers might ask you
to leave your GPS with them for the night. With 100 identical  looking GPS'es
it will become a nightmare to find yours again.

Older GPS models

From 2010 expect that no more GPS tracks will be accepted without altitude info.

Stay away from GPS 12, 30, 40.  Make sure what you get has altitude data in the track log

Make sure your GPS is running up to date internal software.
See for what is the latest level.
Old software levels can cause wrong date stamps ( not Y2k ready ).
Or the GPS stops working while in flight.
And compare your GPS time with the "officail" GPS of a marshal.
To make sure you are not one of those 13 seconds off.

It is up to the pilot to ensure that the track sample rate is set correct.
And the GPS internal software is up to date.

------------ GPS 12 range ---------------------------

Set track sample rate to 15 seconds.
Use MARK and collect a waypoint when is sector to be on the safe side.
Use FILL Mode to preserve the track

Set Arrival alarm to 1 km or less to be sure you are in sector radius if FAI is used.
For  cylinders of 400 meters , modify the alarm to 400 meters, if you use it.

Choose ZOOM to  1.2 km to see the  1 km FAI sector.
Or 0.4 if we use Beercan Cylinders with 400 meter radius.

Do not play with the contrast, keep it maximum.

--------- GPS 38 ----------------------------------------------------

Small track memory, you might have to switch off during flight.
Track sample rate 30 seconds to high for catching a turnpoint sector.
Use MARK to collect waypoints when you think you are in sector.
Confirm with organizers before the first task what methods you can use to verify your flight.

------ eMap ----- eTrex ------------------------------------------------------

eMap  and eTrex got sound like they have a big memory.
But it might not all be available for your current track. And can get filled up too fast.

DO NOT SAVE your track, it deletes the time info and sets it to -1 ! And reduces the amount of track points.
Use battery save mode, otherwise every 1 second one collects a track point.
What will give you less than 1 hour.

Or set the sample rate to distance instead of automatic mode.

More eMap info:
The automatic tracklog recording criteria that is used in our GPS's is based
on a resolution figure (normally 82ft). Basically the GPS projects a
possibly location from your current position based on your current course
and speed, if the next GPS fix differs from this projected location by more
than the resolution figure, a new point is added to the tracklog.

So if you are following a steady course and speed, less points are recorded
than if you were maneuvering a lot.

Marked waypoints do not get a date and time stamp.
Without any date and time info a waypoint from an eTrex or eMap can not be used for checking if a waypoints fits into the track log.


eTrex Vista

1. Moving Map display

2. Altimeter pages that show descent/ascent rates

3. GPS tracking for competitions

First off, the display is too small to use the moving-map in flight, because
I need to zoom out to see where I am, and then zoom in again to see
"exactly" where I am, as zooming out leaves the details unreadable. As an
added blunder, I bought the Garmin MapSource Topo software. Nice to have on
the PC, but downloading maps to the Vista is a waste of time (in my opinion)
because the screen is too small to really see any topographic features. On
the other hand , it does transfer the map data at 115000 baud, so it doesn't
take days to fill up the 24 megabytes of memory. The Vista comes with a base
map that has all the highways, and a lot of secondary roads. Highways are
labeled, but all the other roads are just called "Road", so the supplied
base map will not help you direct someone with a map to your location.

The altimeter pages are great, especially the one that shows your elevation
changes over time or distance. I found that using the elevation changes over
time was most interesting. The time window is adjustable; with a 2-minute
window, the display gets a new altitude plotted every second. Buttons are
easy to use in flight with gloves on. Nearly all the functionality is
reachable with the "click-stick" on the face; this was especially easy to
use, except when it got a little bumpy!

Where this unit really shines is the GPS tracklog. It hold 3000 data points,
and recording frequency can be automatic (four modes defined by Garmin: Most
Frequently to Least Frequently), or you can choose your own recording
frequency based on distance traveled or time. By setting the unit to record
every 12 seconds, you guarantee that you'll be recording for 10 hours,
probably the maximum amount of time one would need? If not, the time can be
set to every second as most frequently, up to X days for those reall long
flights. However "saved" tracks only are 250 points long, so you will lose
>90% of your tracklog data if you save it to "saved" track log instead of
transferring the "active log" to another device (PC/Palm/etc).



The lithium battery draws a small charge from the alkalines to recharge.
When you leave the GPS without alkalines, the lithium can go flat (after a
few months). This means losing the data stored.

The lithium cannot be replaced in any GPS's except a GPS II Plus, III Plus
and Street pilot (or presumably any GPS looking like those). It is therefore
not possible to replace it in 12's and the other types.

If you have a new 12 (still under warranty), they will replace the unit. If
it is no longer under warranty, then you might get about R400 off your next

However, if your internal lithium battery has gone flat, then all may not be
lost. Replace your alkalines and leave them for about 5 - 7 days. If it is
not damaged or the unit is not damaged, then your lithium may get recharged,
and your unit will function normally again.

Make sure that the alkalines that you leave in are not leaking, or cannot

The unit communicates at 9600bps, so the people who want to hook it up to
their laptop or radio for displaying their position second-by-second can do
so. It comes with 24 megabytes of memory for map download. I still need to
explore battery options, my cheapo Ni-Cads only go for about 3 to 3.5 hours,
which is long enough for most days since I have a few sets, and usually land
after a few hours of fighting with the thermals, but won't do for those long

For me, this unit is perfect, as it has some vario capabilities combined
with GPS. For those who already have a vario, the added expense of
moving-map display, pressure altimeter, and electronic compass may not be
worth the $300 price tag when compared to the (Ebay) price of a Garmin 12.


  from FAI IGC website,  IGC files have to use UTC time ...

GPS system time - is the continuous and highly accurate time kept by the GPS satellites. It began as UTC
for 6 Jan 1980 when the system first became operational, and maintains that time frame. It does not change
with the 'leap seconds' additions that are made to UTC to allow for the slowing down of the Earth's rotation
(see under UTC). In year 2000, UTC was 13 seconds later than GPS System Time. However, the GPS
system keeps track of leap seconds corrections, and these are sent as part of the satellite's message to users.
Most receivers use the GPS satellite message automatically to compensate and output UTC rather than GPS
time. In some GPS receivers, stored track records do not take leap seconds into account and output in GPS
system time, whereas NMEA data outputs generally include leap seconds and times are corrected to UTC.


  How to improve your score ( some call it cheating)

Hand in an old backlevel GPS which has the 13 seconds difference. It will give you a 13 seconds advantage in start crossing. Good devices are old Garmin 38, 40 or 12 4.0 SW level.  Also MLR and old backlevel Aircotec TN units can do this for you.

In 2008 the time difference is 15 seconds.

You can start 15 seconds earlier, but when you get to goal your goaltime will be some seconds behind some other fellow who , in fact, landed after you. If you are one of those pilots who have to fly with a backlevel code version,  make a big fuzz when you get to goal. Make sure everyone sees that you landed before this guy. Have witnesses. Then, at scoring, complain and moan about the software, and refer to your witnesses. With the help of handing over a few beers the scoring staff will then feel obliged to fix the score in your favour.

If the ES cylinder is the same as the Goal cylinder then calculate your best glide to goal  not to the center of the goal. But aim for the edge of the 400m radius.  And if you come short run the last few meters over the cylinder radius. If you are good in juggling , throw you GPS up in the air while doing this to change the altitude value to make it look more realistic on the track log. From an organizers point of view, make the ES a 1km cylinder around goal. 

How to mess up your score

GPS devices use a different formula to calculate the distance to a turnpoint than the scoring code.For example a Garmin might use WGS84 with  certain ellipsoid values. While the TP scoring code uses an FAI distance formula.Your GPS might say you got the cylinder, while the scoring code reckons you are a few meters short of the radius. Cater for a 40 meter difference.

Do not assume when the GARMIN GOTO arrow switches to the next turn point that you have been in the cylinder sector for the turnpoint. If you fly with a GPS12, set your Zoom to 1.2km and wait until you enter the inner circle. Or with other GPS, when the arrow has switched already to the next turnpoint, change into a map mode that can show that you get within the 400 meter radius.

Not using dd mm.mmm can give you a 20 meter error. GPS devices work on a default of WGS 84 and dd mm.mmm. If you choose to use something different, then you get some rounding errors when the device transforms to other units. It might tell you that you are in, but what it stores is still outside.

Flying with the Garmin set to AUTO Track log collection in WRAP mode, getting to goal , and guess what ,.... your beginning of your flight is missing! Never use AUTO mode, if you can avoid it. If you got a unit which only does AUTO mode, switch it off when it is not required.

Not clearing your track log before take-off and flying  in FILL Mode. A very good way to make sure to avoid winning the competition.

Nearly as good is screwing up your track sample time setting.

Got one of those newer GPS with a biiiiiig memory? Set it to 1 second sample rate if you  fancy the scoring staff and need an excuse to chat them up. With a 1 second track sample rate you will spend a lot of time at the computer while waiting for the tracklog to download. And then witness to see the track processing code crash. 

If you want a very fast download, develop some finger trouble and set your sample rate to one track point per day. That makes sure you track log will never fill up. And your 0 score is processed very fast.

A good one is also to keep your GPS switched on after landing.  Giving the GPS a chance to overwrite your flight.

Talk the Score talk

On the results you see the following abbreviations

 NYP = Not Yet Processed

 ABS = Absent , means pilot was not on takeoff , Absent pilots are not taken into account for the minimum number of pilots to have a valid task

 DNF = Did Not Fly,  gets 0 points if it is a valid task. If a lot of pilots are DNF, then task might not be valid

 LO = Landed Out,  you get measured from the next targeted turnpoint towards the closest you got to that turnpoint.

  You  can fly towards the next turnpoint, decide you do not make it, fly back and land in some decent spot. You do not get scored where you landed.

   But if you are serious about winning and getting points, you keep on flying the task. And do not bother where you end up. Be it a tree or in hospital.

   If you tear your glider in a tree, or smash yourself up, you still get scored. And eliminate yourself out of the competition.

   Unless it is the last day, and you reckon it is worth it.

 GOAL = You made it to goal and the time when you crossed the End of Speed Section (ES) is used for your score. Not the time when you landed in goal.

  ES = End of Speed Section is nowadays a 1km circle around GOAL. If you land after crossing ES but not in Goal, then you get a slightly less score.

    Reason why we have an ES of 1km. The pilots cut it so fine, that they have no time to land properly if ES is at Goal.

  SS = Start of Speed Section ,  normally a circle around the 1st turnpoint. One has to wait outside until the Start Gate opens in a Race to goal task.

     Can also be a circle around takeoff. And one has to stay inside it until task window opens.

  Race to Goal = One can not cross the SS before the Start gates open. Then everyone races to get to goal, using that opening time.

      If you cross over the SS later than the opening time, tough, you wasted time.

  Speedrun , also called Elapsed time =  After a certain time you can cross whenever you like over the SS. And that time gets taken.

    You might launch late, but due to better thermals can fly faster, arrive later than the first pilot in goal, and still win.

     This type of task is not very popular. Most top pilots like to race against each other and know who is at goal first.

Turkey = Turkey Patch = an area designated below takeoff where one can easily land without finding any lift.

   Landing in Turkey makes the pilot a turkey, and allows the pilot to come back to takeoff and relaunch.

   If you land outside of turkey, you can not relaunch and try again.

Minimum Distance Set = to reward pilots who took off and sank out and landed in turkey, they get a minimum distance, that they could have glided anyways towards the next turnpoint. To encourage pilots to take off, be wind dummies, and try again afterwards.

Validation Distance =  a certain amount of pilts have to fly a certain distance to make a task valid. Sometimes the weather deteriorates. Gets worse.

 The pilots who launched early got away and the rest can not launch.

 Or sometimes the first batch all sink out. And only a few , who launch late get away.

Tiger Line = ( refering to Tiger Woods )  a straight line flight path with no turns required to fly straight to goal. Sometimes happens.