Site Engineer question

mail

Hi I have no experience in survey equipment but I need to know how I can calculate a bearing. The bearing from point D to point C is 346 deg and the bearing to a set out point is 51, deg how can I calculate the set out bearing when I set the instrument at 00 while sighting to point C ?

Supertech

Is the bearing from 'D' to the set out point 51 degrees? If so, there's a difference of 65 degrees between the two bearings. However, it depends on the way the instrument is set up. It may be set up to work clockwise or counter-clockwise. If you set the instrument to 00 while back sighting to the known point try working to a bearing of 65 degrees and see if that works if it doesn't, then try working to a bearing of 295 degrees. You'll obviously need to have some idea where the set out point needs to be so you can check it. If you have an Autocad drawing you could try setting it out using coordinates.

mail

Thanks for the quick reply, to be honest we are doing an introduction to the setting out and I cant contact anyone to clarify. The bearing is 346 deg from point D to C. The calculated bearing to a set out point is 51 deg (plus minutes & sec.) we were told the calculated bearing minus the given bearing will give you the bearing from north. I want to sight the instrument to point C from point D and set it to north, then turn clockwise to set out point. To me it doesnt make any sense 51 - 346 = -295. I didnt know you could imput a minus into the theodolite, thanks again.

Supertech

Sorry - my mistake. I assumed you were using a total station. Anyway, 360 - 346 = 14 degrees (360 being a full circle). 14 + 51 (the calculated bearing) = 65 degrees. Then if the set out point is left of the known point set the bearing to 65 degrees, if its to the right, set the bearing to 295 degrees (360 - 65) ....... I think !! :D

mail

Thanks for that, just one question, does the horizontal circle not turn the same as on a compass, i.e turns RIGHT 90 deg then 180deg ?

Supertech

They may do when using a theodolite. I generally use total station, and it's always been set up to work in the opposite direction and I've never changed it. If there's a diagram of the setting out problem your working on it should clarify that issue for you anyway.