Three Point Resection

A three point resection can be done with Party Chief using the RESECT3 program. This extra program can be loaded into the User Keys menu of Party Chief following the procedure described in your manual.

A three point resection uses angular data measured to three known points, usually fixed points on the horizon such as antennas or mountain peaks, to compute an instrument location. The best solution is generally when the three points are spread out as widely as possible, such as when they completely surround the instrument location.

The RESECT3 program requires input of 3 point numbers plus a measured angle to each of these three points.

To the best of our knowledge points and angles may be entered in any order, and it is not required that you zero on any particular point, or even at all. If you encounter problems, we recommend that you try shooting the points in a left to right fashion, zeroing your instrument on the first point. This is probably the most common practice.

After the resection is computed, occupied coordinates are returned to the stack in levels 1 and 2, backsite azimuth and bearing are returned in levels 3 and 4, and an error is returned in level 5. The current instrument position and backsite are updated internally to reflect this data. The error represents the difference (in ground units, ie feet or meters) between the calculated distance from the center sighted point to the occupied point based on the left and right triangles formed by the additional sighted points. If this value is larger than the accuracy to which you try to position your instrument (ie 0.01 feet) you should perform additional checks to verify the computation.

Note: You should always perform additional checks to verify the accuracy of any occupied position, such as checking stakeout ties to known positions and verifying computed against field data. This is especially important when performing resections.

A three point resection can not be calculated in the case where the three points and the occupied point have a common radius point. As this case is approached the results become increasingly inaccurate. This is easily avoided by sighting 3 knowns which completely surround the occupied point, so the occupied point falls inside the triangle.

[RESECT3 User Key] Press the user key that the RESECT3 program was loaded on. If you don't know which key this is then press [USER KEYS] to see which key it was loaded on, and select the appropriate key.
This program utilizes dialog boxes which use the up and down arrows for input.
Enter the appropriate point numbers and horizontal angles to the three resection points.
After all the data is entered press the softkey

Coordinates for the occupied point are returned in levels 1 and 2 of the stack. The backsite azimuth and bearing are displayed in levels 3 and 4. The backsite is based on the angle measured to the first point. The calculated error is displayed in level 5. You will need to roll the stack down () or DROP the stack to see the error.