Questions and answers about collecting and processing measurements with total station

Resection with 4 points

If you have four control points on the field, will you do resection including 4 points or just use 3 to set up resection, and check shot on the fourth?

Let’s try to answer it!

The goal of resection is to determine the total station’s position and orientation by observing known control points (backsights). The configuration and number of these points directly impact the accuracy of the solution. The more accurate and geometrically well-distributed your control points, the better the result.

There are two options:

• Option 1: use 3 points and leave 1 as “truth” for checking
• Option 2: use all 4 points and let total station software tell you error of the position of the total station .

Option 1: use 3 control points for resection, 1 as a check

Pros:

• Provides an independent check shot for validation.
• Helps identify outlier control points or input errors.
• Supports industry best practices for QA/QC.

Cons:

• Slightly reduces the strength of the mathematical adjustment.
• May be less effective if the check point is poorly positioned.

Option 2: use all 4 points in the resection

Suitable when geometry is suboptimal.

Pros:

• Increases redundancy and strengthens least-squares solution.
• Useful when point visibility is limited or geometry is constrained.

Cons:

• No independent check — harder to identify faulty points.
• Requires close inspection of residuals and error propagation.

Geometric considerations

The spatial distribution of control points is critical:

Always strive for a well-distributed polygonal layout around the instrument for best results.

Tip

If your software supports residual output:

1. Run the resection using all 4 points.
2. Check residuals — if one control point shows significantly higher error, exclude it.
3. Re-run with the best 3 and use the excluded one as your check.