In practical engineering surveying, measurement points are often constrained by site conditions. In many cases, it is not possible to place the prism directly at the designed center point of a column or structure.

If eccentricity correction is not applied, these offsets will introduce systematic errors into the measurement results, which may affect subsequent construction layout, as-built surveys, and final project acceptance.

ColumnOffs (Column Offset) is a dedicated total station function designed to address this challenge by calculating the true center point based on measurements taken from accessible locations around the column.

1. When Should ColumnOffs Be Used?

ColumnOffs is typically used when the center point of a column (P0) cannot be measured directly, but circumferential points on the column surface can be observed.

If the prism can be placed on accessible circumscription points (such as P2 and P3) around the column, the total station can calculate the center point based on these measurements.

By measuring two points on opposite sides of the column:

• The coordinates of the column center (P0) can be calculated

• The direction angle of the center point is obtained as half of the total direction angle between the two circumscription points

This method allows accurate center determination without direct prism placement at the design point.

2. How to Use ColumnOffs on the STSA9

Follow the steps below to perform a ColumnOffs measurement using the STSA9 total station:

a. Center and level the total station, launch the Android TS software, and complete station setup.

b. Open the Collect menu and select the ColumnOffs function.

c. In the ColumnOffs interface, enter the point name, point code, and the prism height used for measurement.

d. Aim the total station at the prism positioned at P2, then tap OK. The instrument records the coordinates of P2.

e. Move the prism to P3, aim again, and tap OK. The instrument records the coordinates of P3.

f. The system calculates the column center based on the two measured points. Align the instrument as required to complete the operation.

The ColumnOffs function provides an effective solution for column center measurement when direct access to the design point is not possible. By using circumscription points, surveyors can reduce eccentricity-related errors and improve the reliability of construction layout and as-built measurements.

We hope this introduction helps you make better use of the STSA9 total station in real-world surveying scenarios.