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I'm interested, so please share it.
----- Original Message -----
From: "Royer, Doug" 
To: 
Sent: Monday, March 24, 2003 12:15 PM
Subject: Horizontal distance off measurements


> On 03-17 @ 212624 hrs. Mr. Kenchington wrote that one cannot use sextant
> horizontal angles to find distance off measurements or bearings.I must
> differ with his opinion.Perhaps he did not understand  or misunderstood
what
> I was trying to explain.
> The following is a simple explaination of the proceedure taken from the
> books "Elements of Navigation" pgs. 140-143 by W.J. Henderson and "Coastal
> Pilloting"pgs.89-93 by Commadore R.P. Ferchew.Each book has multiple
> examples of the proceedures ranging from a simple 90* angle solution to
> complex solutions for acute and obtuse angles.
> Using the simple example of one of the objects @ 90* from the observer and
> table 31,Bowditch and a calculator I did the exercize.I then used a UTM
> projection and using 10 digit coordinates measured the distance between
> electrical towers.I then calculated the distance off 2 of the towers and
> fixxed a position.To keep the evolution simple I kept the 3 objects as
close
> to parrallel to my LOP as possible.Useing a handheld GPS I then went to
the
> calculated position fixxed from the projection.Using a sextant I then took
> the Horizontal angles of the towers.I also took the bearings of the
> towers.After the calculations were complete I used a laser rangfinder to
> measure each distance.The delta between the chart measurements,sextant
> measurements and the laser measurements were 5 ft.on the longest leg
> distance and 2* T on the bearings.To me that proves one can get accurate
> distance off and bearing measurements from Horizontal sextant angles.
> The example:
>                                                   C                    A
> B
>                                                    .                     .
> .
>
>
>
>
>
>
.
>                                                                          O
>
>
> Useing dividers measure the distance AB = 300yds. AC = 307 yds.
> Useing the sextant find the angles AOB = 11* 32' 13". AOC = 11* 47' 33"
> dist. off OB = 300yd./(sin 11*32' 13") = 1500 yds.
> dist. off OC = 307 yd/(sin 11*47' 33") = 1502 yds.
> Set dividers to 1500 yd. and swing an arc from B.Set the dividers to 1502
> yd.and swing an arc from C.Where the 2 arcs intersect will be your
> approximate position.Using parrallel rules find the bearings in * T of OB
> and OC.Take the dividers and measure the line OA.This will be the distance
> off A.One can calculate the dist. off A = 300 yd./(tan 11* 32' 13") =
1469.7
> yds.
>
> A = 307 yd./(tan 11* 47' 33") = 1470.5 yds.
> There is also a nice technique for finding the ballpark distance off an
> object over terrain useing a mil type lensatic compass I have used with
good
> results.If anyone is interested I will share it with you.

   

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