[OSM-newbies] Triangulation using GPS w/ magnetic compass

[Bill Ricker]

On Wed, Mar 11, 2009 at 8:09 AM, Matt Maxon <osm at mattmaxon.com> wrote:
> Kelly Jones wrote:
> As others have said... No the GPS isn't a suitable surveying instrument
> The Pocket Transit
> http://en.wikipedia.org/wiki/Brunton_compass

yes. having tried the Lensatic infantry map reader's compass, I have
one of these mapmaker's/surveyors pocket units on order for this sort
of purpose, whether useful to OSM or not.

> This is one inexpensive

relatively. good ones cost about the same as good GPS.
http://www.thecompassstore.com/pockettransit.html

cheap plastic ones without extended base peep (thus less accurate) are
cheap like cheap gps http://www.thecompassstore.com/cadet.html

military surplus if in good condition are the best buy.

> and used properly accurate device

yes

US army WW2 training&field manuals for map-reading have some info but
more is in artillery reconnaissance and field mapping manuals, where
calibration and use of the  military model for actual surveying is
discussed.

> It can be mounted on a tripod which IMO is essential for this type of
> surveying

note you need a non-magnetic tripod to avoid disrupting the compass.
not sure if the exclusion of magnetic lines in Aluminum is strong
enough effect to be a problem or not.

For approximate work, one can avoid trig with the Brunton 6050M Pocket
Transit  or US M2 Artillery Compass (same unit, some manufactured by
Brunton, some by others in wartime)  which is calibrated in Mils
(meter deflection at kilometer range) but it will run 2% over in the
range where sin x = x approx holds. But one can still use Mils trig
when needed.

It feels good to finally understand why Mils are the natural metric
angular measure.

-- 
Bill
n1vux at arrl.net bill.n1vux at gmail.com