by **Jason Poitras** » Fri Oct 08, 2004 4:09 pm

Hello,

You're correct. Using your sample observations the average horizontal angle will be 90°. When I input these observations into FieldGenius 2004, it also computes an horizontal angle of 90°.

I think I know where the confusion is and why you think it is computing an incorrect angle. When you review the shots in FieldGenius, we display the average direction, made up of your direct and reverse reading. When I used the observations you described and reviewed the foresight shot it displayed the following information on the screen:

FS Point: 50 F1=1 F2=1

Std Dev: HA 2.5" VA 0.0" SD 0.00'

HA 90°00'03" VA 90°00'00" SD 100.00'

BS-FS Angle: 90°00'00"

The 90°00'03" is the average reading to the foresight and doesn't take account the backsight. Just below it we show the computed HA angle taking into account the backsight readings.

When I look at the raw file I see the following:

--MultiSet

OC,OP52,N 5424490.1270,E 443079.1820,EL71.8040,--

SP,PN50,N 5424653.5080,E 443076.0040,EL69.9170,--

BK,OP52,BP50,BS358.53084,BC0.00025

RB,OP52,BP50,AR0.00000,ZE90.00000,SD100.0000,HR0.000,--

RB,OP52,BP50,AR180.00050,ZE270.00000,SD100.0000,HR0.000,--

RF,OP52,FP100,AR90.00000,ZE90.00000,SD100.0000,HR0.000,--

RF,OP52,FP100,AR270.00050,ZE270.00000,SD100.0000,HR0.000,--

SS,OP52,FP100,AR90.00025,ZE90.00000,SD100.0000,--

If you look at the SS record the angle right is 90°00'03" which might lead a person to believe that the angle was computed incorrectly. But... You have to take in account the backsight reading which is represented with the BC code in the BK record. So if you take the (AR - BC) which is (90.00025 - 0.00025) the result is 90°.

I hope this answers your question.