"Wildepad" <noreplies> wrote in message

Now it can't just figure out it's basic spot but also what angle it is

to a baseline -- that is, it isn't enough to say that it's 83 feet

from tower #1, 212 feet from tower #2, etc., it also has to read out

that it is 18.42 degrees to the line between towers 1 and 2.

In other words, on a map with the towers plotted, it must be possible

to determine exactly where the unit is _and_ where it is pointing.

'Absolute' accuracy is not as important as repeatable and relational

accuracy -- that is, it can read 83 feet from tower #1 when it is

actually 82.4 feet, as long as it always reads the same thing at that

point and it reads 41.5 feet from that tower when it is exactly half

as far away (when it is actually 41.2 feet away). ((Does that make

sense?))

The complete unit has to be no more than $1500, and the towers with

transmitters no more than $500 each

Any constructive answers appreciated.

After several days, we have determined that you really want angular

measurament accuracy, but $700 is too expensive (TCM2.5 compass) to achieve

0.1 degree accuracy because it busts the budget for the entire system.

You state you want to determine the angle to the straight line that connects

two towers. You do, of course, realize that every point on that line is at a

different horizontal angle from your roving unit. Are you asking to

determine the angle that a beam will intersect the line? If so, a compass

tied to each unit still may be your best bet.

Other alternatives (some may border on the ridiculous):

- Make the "pointers" long enough so there is a definite position

difference between the from and back; mount a GPS unit on each end and

compute the angle between their positions (expensive).

- Mount one or more accelerometers in the units (at the end closest to the

beam output) then, starting with the units pointing in a known direction

(you need to know what that direction is), the data from the

accelerometer(s) could be used to determine speed and direction of movement.

Compute angular difference from the starting point. Using one accelerometer

for horizontal movement and one for vertical movement, you will be able to

determine both the geographical point of intersection and the altitude of

intersection.

The above would require some way to obtain and process the data. The units

could be hardwired to a controller unit or, that being impractical, you

could use a wireless system (Bluetooth, etc.).

Perhaps more importantly, what accuracy in the direction it's pointing

could be reached? (i.e. if there were two such units, and you plotted

their readings on a map in a computer, could you determine whether

laser pointers attached to them will cross 250 yards outside the

triangle?)

Assuming the line runs east-west, if your two units are inside the triangle

(south of the line) and the beams bisect the line at any angle between 0.1

and 89.9 degrees for the left-most unit and 359.9 and 269.9 degrees for the

right-most unit, you can be sure the beams will intersect at some point if

the units are at the same height and vertically pointing at the same angle.

The intersection point will be determined by the positions of the two roving

units and the angle they are pointing. Distance between the units and

distance to the line both come into play. Trig will, once again, be useful

in determining where they will intersect.

If I still don't understand what you are trying to do, maybe you could be a

bit more specific about what you are trying to accomplish and seeing if the

folks in this group can give you other ideas of how to do it.

Accuracy can be expensive. Don't get discouraged, just research as many

alternatives as possible.

Good luck, no matter how you end up approaching this.

Richard

Old guy; perpetual student