"KBH" wrote in message
.. .
....
I have posted a law-of-cosines calculation example several times where
coordinates of an intersection point are determined from two GPS locations
with a bearing from each location...to the intersection point. I can find
one of those in my files and post it later if that is needed.

The free software FAA software compsys21 will do this and more
http://www.naco.faa.gov/index.asp?xm...online/compsys

"KBH" wrote in message
. ..
The free software FAA software compsys21 will do this and more

That's interesting but for something the size of half-a-state I would more
likely work with UTM coordinates and then use plane survey formulas...

Why use an inaccurate approximation when better software already exits???

In RDF navigation the more "fixes" one has the smaller the
ccccircle of confussion. For a variety of reasons, measurement
erros, propagation anolomies etc, the bearing is seldom perfect.
These imperfections create a difussed "circle" that the calculated
powiton lies witihin. Moer sighting/bearings gives smaller errors,
but using home built equipment one shouldn't expect world class
accuracy.

As a basic check pick a non NDB,make your measurements,
being carefuyll to note the GPS reading for each, and see how
close you come to hitting the transmitters location.

I su pect that yoru antenna will be far from accuarte with some
imbalance. that will be hard to quantify exactly. As a fun project,
that will teach you a lot about navigation go for it, but as a serious
attempt I suspect you will be dispointed.

Even at NDB low fRF frequencies, there are too many things
that will cause transmission path errors. I live about 15 miles from
the Lexington Blue Grass Fild NDB and even with a barrowed
mil grade RDF setup it's apparent bearing changed by several
degrees the month I had the unit. The NDB in Frankfort and Mt.
Steerling "wondered" all over the place. with sudden randon sshifts
up up to +/- 5 degrees. The pilot who loaned me the unit told me that
the closer to the earths surface you got with a LF RDF the more error
you
pikced up. At 5000' the error was very small. This was 25 years ago
and I suepct not much has changed.

This was an aircraft RDF and at that time still was within the
calibration cycle.

Good luck and have fun.

Terry

The free software FAA software compsys21 will do this and more

That's interesting but for something the size of half-a-state I would
more likely work with UTM coordinates and then use plane survey
formulas...

Why use an inaccurate approximation when better software already exits???

You give yourself away with a comment like that...

Projections to rectangular grids are not intended to be approximations but
are intended to be rectangular grids.

Latitudes and longitudes labeled on an atlas are first converted to
rectangular coordinates, plotted as rectangular coordinates, and then
labeled as latitude and longitude. In other words any point (within range)
has both latitude / longitude location and UTM grid location. Simply there
is a conversion between the two.

Okay, UTM and geodetic have different directional orientations. But in
project layout any point is relative to two or more other points. In project
layout there is no such thing as one point relative to only one other point
because that would be a magical creation. The point is that UTM directional
orientation is used with UTM points and that geodetic directional
orientation is used with geodetic points. (For example, the consumer GPS
user can do this by getting their GPS location, getting a GPS location of a
skyscraper or transmission tower that can be seen in the distance, and then
laying out an angle to a required point using their home point location and
the line of sight to the tower. Note the three points and that is project
layout.)

Also, a bearing in UTM is one direction to the point. And that is likely
what is required on a project. A geodetic bearing is simply a beginning
direction to the point and directional corrections are required. That may be
okay for navigation but would very strange in project layout...So a layout
in UTM is a rumb line while a geodetic layout is a great circle. Note that a
point laid out on a rumb line in a UTM grid could after layout be converted
to latitude and longitude. In other words simply meet requirements and
output in any required format.

Of course for higher accuracy, projections to state plane coordinates are
used instead of UTM coordinates. And state plane coordinates are used
extensively in project layout. There are not a bunch of engineers walking
around saying "...why use an inaccurate approximation..." as the project is
simply defined with a rectangular coordinate system.

Finally, one benefit is using rectangular coordinates are that simple
formulas can be used with rectangular coordinates. Someone with an
inexpensive scientific calculator can make on-site calculations that for
instance a construction crew might be waiting on. And of course a $90 HP48
will hold and quickly run all of the plane survey formulas and will fit in
shirt pocket. Furthermore, plane survey formulas can be developed for PC
programs in short periods of time and without access to highly developed
formal sources of information or expertise.

So if the project is defined with rectangular coordinates why have a
software that does not apply to the task ?

"KBH" wrote in message
...
You give yourself away with a comment like that...

With a PhD in mathematics specializing in an area of geometry, I think
you
misjudge me.


The terminology "...in an area of geometry..." is another give-away.

Geometric topology with graduate coursework including differential
geometry--in that you learn the substance of approximating a curved surfaces
with euclidean pieces ("maps"). And yes, I have actually studied the
differences in distances and angles from approximating the earth's surface
as rectangular on the small scale--not in a course but by doing the
calculations.

But that's not the point.

Agree.

Projects are not defined with great-circles because the direction to a
great-circle is just a beginning direction. Navigation on the other hand
seeks the shortest route and thus correction of the course is accepted. So
projection to rectangular coordinates systems is used for projects while
geodetic systems are used for navigation.

As I understand the original problem. it was to triangulate to locate one of
the NV beacons and the software I mention contains menu selection that will
do the needed calculation.

I would argue that rectangular coodrinates are used simply because we like
to think in straight lines, they are easy to construct, and on a small
scale they approximate a geodesic (great circle) on a sphere.

I might add that I have done long range triangulation of VLF stations (the
stations were 1000's of km away). This would have been impossible using
rectangular coordinates. Additonally, originally the FCC HF DF network had
to use a special device to triangulate--it would have been much easier if
they could have just done rectangular geometry. But again, the distances of
the project proposed are much smaller and that level of accurate modeling is
certainly not needed as other errors will be more significant.

Per the original plan, I like his differencing the angles from a known
source as that is better than just trusting the null to be where he things
it is in the antenna pattern. Ideally use a radio where one can turn off
the AGC--it will make things a lot easier. Be sure to make several (lots)
indpendent measurements at each location and average them. If you take
enough (ideally at least 30), you can then construct error bound for the
bearings using simple statistics. And the thing usually forgotten, practice
the technique on known locations (beacons) first to obtain realistic
expectations..

As I understand the original problem. it was to triangulate to locate one
of the NV beacons and the software I mention contains menu selection that
will do the needed calculation.


I don't dislike using the geodetic software to determine the intersection
point but as I said before I personally would work with UTM coordinates and
a simple law-of-sines calculation. The law-of-sines calculation could be
demonstrated in a small paragraph while the ellipsoidal intersection
calculation would be a page of formulas.

The final result of working with UTM is UTM and can always be converted to
latitude and longitude.

Also, with rectangular coordinates the problem could be worked out on graph
paper...or as I said before worked out graphically.

But suppose the compass readings were perfect and the distances involved
were 40 miles...and say that the becon is the size of a 16d nail and that
determination of its location is critcial within two diameters of the becon.
Is the compass pointing a rumb line or is the compass indicating an initial
direction ? In other words with the geodetic software are we seeking the
intersection of two great-circles or the intersection of two rumb lines ?


I would argue that rectangular coodrinates are used simply because we like
to think in straight lines, they are easy to construct, and on a small
scale they approximate a geodesic (great circle) on a sphere.

We do more than think in straight lines. Survey instruments run straight
lines or determine straight baselines. A control survey is points connected
with lines even though points on some curve near the control survey can be
set from the control survey...

The historical requirement of the division of Federal lands calls for the
construction of an East great-circle as points offset from a straight
baseline...In other words the straight baseline is the given and the
great-circle is the construction.

The routes intersect on the map.That is, you have to enter a waypoint
where the lines cross.

Indicentally, I think UTM is much better system, but it is sort of like
Betamax and VHS.

It's probably loaded to increase the electrical length. Here is a
photo:
http://www.lazygranch.com/images/basecamp/ndb1.jpg
I cranked up the contrast, but you can't see the wire.

I've run into state plane as well. I believe they work in feet, which
is one of the differences between state plane and UTM. However, my
knowledge of either is pretty limited.

http://www.lazygranch.com/images/fau...rojfault-3.jpg
I found this marker and was baffled about the coordinate system until
someone on this group pointed out it was in state plane coordinates.

I know of a Jim Gosnell who lives in Florida.You any kin to him? He was
in Vietnam.Which reminds me,I got an email from him yesterday and I need
to reply.About updating an email list.
cuhulin