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## Re: Accuracy of radio/GPS-like system?

 Subject: Re: Accuracy of radio/GPS-like system? ehsjr Thu, 13 Oct 2005 13:59:42 GMT sci.electronics.basics
 ```Jasen Betts wrote: ``````On 2005-10-12, ehsjr <[email protected]/* */> wrote: ``````How about determining the angle optically instead of with the GPS? A laser pointer and protractor can give you the relative angle from the handheld unit to each of the antennas. But your description of the angle needed is incomplete. A point can't have an angle with respect to a line. For example: `````` He wants to know which way the handheld unit is pointing WRT some baseline. `````` Yup. And you can't solve that problem until "handheld unit" is given some detail. For example, which way is the handheld unit shown below pointing with respect to the baseline below it? ------ | Hand | | Held | | Unit | ------ -------------------------------------------- baseline As it turns out, the closer you question him, the more detail comes out. Originally, the handheld unit was "about eight inches square". Now he says it is a square which removes some ambiguity, and the second line is the front edge of the square, removing the remqaining ambiguity. And he adds that he needs accuracy to about 1/4 degree. `````` `````` HandHeld_Unit A-------------------------------------------------B What is the angle of the hand held to the line defined by points A and B? `````` they look parallel to me :) `````` Really? They look perpendicular to me. Let me draw and extend the edge line for you: ------------- |HandHeld_Unit| |------------- | | A-------------------------------------------------B The details are important! His original description was mathematically equivalent to a point and a line. We can assume anything we want - and be completely wrong - until he specifies the ambiguity out of the question. Hell, his reference line on the handheld unit could have been either diagonal of (what turned out to be) a square. Ed ```