REFLECTOR: compass rose

[Sid Knox]

----- Original Message ----- 
From: "Tom" <tomcat05 at comcast.net>
To: <reflector at tvbf.org>
Sent: Sunday, March 22, 2009 6:51 PM
Subject: Re: REFLECTOR: compass rose


> You can't beat GPS accuracy. Why not walk a portable instead of trying to 
> taxi---you can walk it as many times as you'd like for verification. Lay 
> down some tape for a straight line to walk on and try not to drink 
> beforehand.


That is essentially what I did a couple years ago when my son painted a Rose 
at our local airport (KTQH Tahlequah OK) for his Eagle Scout project.

1)  First we did a calibration run or sanity-check by measuring the runway 
as follows:
Pick a spot on one end, let the GPS sit there for 15 or 20 minutes to get a 
good solid fix.  This is point A.  Walk the GPS down the runway about a 
quarter-mile and let it get a fix there as Point B.  Make sure the GPS is in 
the Magnetic mode, not True mode.
 Using the published runway heading, confirm that the line from points A and 
B agrees.  This verifies your technique.

2)  From the center of the Rose, let the GPS find Point C.  Move the GPS in 
some convenient direction about a quarter-mile away and let it get a fix 
there as Point D.  This point must be visable rom the Rose.

3)  Stand at the far side (relative to point D) of the Rose.  Have another 
person stand at the center of the Rose.  Have a third person stand at the 
opposite side of the Rose (between you and Point D).  Move left or right as 
nesessary such that  the center person is directly in-line with the marker 
at Point D.
Using hand gestures, have the person at the opposite side move left or right 
as nesessary to be on the same line.  Now, with all three of you in line 
with the C-D line, you have established a reasonably accurate bearing line 
thru the center of your Rose.  From there, it is just simple trig and 
careful measurements with a long tape-measure to obtain the remaining Rose 
points.  Mark your points with tape, chalk or paint spots.

Don't get too hung-up with accuracy... remember the annual drift of the 
Magnetic Variation.

Sid Knox
Oklahoma

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