Acro Image

Aerobatics Server

ACRO E-mail Archive Thread: Alternative Box Markers

[International Aerobatic Club] [Communications] [Aerobatics Images]

Disclaimer: These aerobatics pages are developed by individual IAC members and do not represent official IAC policy or opinion.

[Usage Statistics]

ACRO E-mail Archive Thread: Alternative Box Markers


Thread: Alternative Box Markers

Message: Re: Alternative Box Markers

Follow-Up To: ACRO Email list (for List Members only)

From: Klein Gilhousen <kleing at>

Date: Tue, 15 Apr 1997 15:13:54 UTC


  At 11:50 PM -0600 4/14/97, Tom R. Myers wrote:
>>without using some form of selective availability correction, you
>>will have about 100 meters of noise in your box.
>actually, many of the latest consumer gps receivers feature averaging
>functions which can get you to well below 100 meters of noise. the
>acuracy depends upon the type of signal processing, sampling rate, and
>the duation of the averaging window. the manual usually spells out the
>accuracy that you will get as a function of averaging time. with
>a long average (a few to 10 minutes), you should be able to lay out
>a beautiful box. you will still have to adjust the corner sighting
>devices by acually viewing down the box edges to account for any
>placement errors. tom.

Note that the dither produces a consistent error, i.e., two units in more
or less the same place will have the same error in position due to the
dither.  So wouldn't it be possible to make your own "differential GPS"
system with two handheld GPS units and a pair of handheld radios?  You
start out with the two GPS's and radios at a box reference point, enter a
user defined waypoint at the same moment and then walk one of them around
while leaving the other at the reference point.  Both units are set to
measure distance and direction from the defined reference point.  You walk
out to a corner with one unit.  When you get there you radio the reference
unit to see what the dither has done in the meanwhile.  Then walk at most a
couple of hundred feet to the corrected point, then check again, etc.
After just a few iterations, you'll be exactly at the desired point.  No
need to use anything but standard stuff you already have plus a hand
calculator to do the geometry.

Klein Gilhousen
Bozeman, MT
Yak-55M N41126


© Dr. Günther Eichhorn
Email Guenther Eichhorn