(2) Use two control points to determine the elevation and coordinates of the suspension points of two thin steel wires.

(3) Turn to downhole measurement.

(4) Determine the elevation and coordinates of plumb hammer according to the length of thin steel wire.

(5) making underground triangle control points

All right!

There is a problem:

(1) The thin steel wire is elongated due to the tensile deformation after suspension, so it is necessary to confirm the elastic modulus of the thin steel wire to correct the elevation.

(2) Coordinate deviation can be corrected by turning point retest and taking the average value of data.