Calculating Azimuth from Variables: dX, dY & Angle

[StarFire]

Homework Statement

Ok, I'm doing a survey course, and I need to calculate the azimuth of an angle. The 'textbook' is a series of not-all-that-well-written notes, so I'm hoping you can help (it tells me that to calculate azimuth I need to reduce to absolute coords, but in order to do so I need the azimuth! ).

I'm not going to post my variables because I don't want you to give me the answer, only to help me figure out the formula I need. I know this is basic trig, but it's been decades since I've studied any trig or physics. I know what an azimuth is, just not how to calculate it from my data.

I know one angle, and the distance between my station point (A) and the point I'm measuring (B). I know the angle is zero because I set the instrument to zero along it.

http://www.tfw2005.com/boards/members/starfire_mk2-42816-albums-misc-retribution-files-picture1583-01.jpg

I know point B is in the 4th quadrant, with -dX and +dY values. Intuitively, this means my AZ will be ~ the 300* range. Problem is, while I understand both the rectangular and polar coord systems (I suspect this is a polar coord system I'm working in, since I have a -dX angle), I don't know how to calculate dX and dY.

Homework Equations

Polar angle theta =tan minus 1 (dX/dY) +addition constant

If this is the right formula, how do I calculate dX and dY??

The Attempt at a Solution

 

[LowlyPion]

Welcome to PF.

Sounds like your 0 line is known, so your azimuth angle to your object in question sounds known as well. (The angle from that line to the line pointing at B.)

To transform coordinates:
http://en.wikipedia.org/wiki/List_of_canonical_coordinate_transformations#2-Dimensional

So if you know θ and r, looks like you can transform that to x,y.