Overview

Accurate layout depends on a strong control network that aligns the digital layout file to the real-world jobsite. When control points are poorly placed, inaccurately surveyed, or inconsistently recorded, the FieldPrinter will surface warnings through error and difference (delta) values.

This article provides a practical troubleshooting guide to help you diagnose and correct control point issues so your control network is stable, reliable, and aligned to the jobsite.

Symptoms / What You’ll See

• High difference (delta) values during stationing
• One or more control points showing significantly higher error than others
• Layout appears rotated or shifted relative to the slab
• Good alignment near some control points but growing misalignment farther away

Why This Happens

Control issues almost always originate upstream of the FieldPrinter. Common causes include:

• Inaccurate surveyed points caused by prism placement, equipment tolerance, or surface conditions
• Too few control points, allowing one bad point to dominate the alignment
• Poor spatial distribution, such as points clustered in one area
• Mixed elevations, where control points are not all at the same Z-height
• As-built changes on site conditions that do not match the original survey

The FieldPrinter does not guess or stretch the layout to fit. It uses a best-fit alignment across all recorded control points, which makes problems visible instead of hidden.

How to Fix or Prevent

Use the steps below to diagnose and strengthen your control network.

1. Increase the Number of Control Points

• Capture more than the minimum of three points whenever possible.
• Aim for 5–8 control points per station in active layout areas.
• Additional points reduce the influence of any single bad point.

Adding more points will not hide errors—it helps isolate them.

2. Check Spatial Distribution

• Ensure control points are spread across the layout area.
• Avoid clustering points along one wall, grid line, or corner.
• Never record control points that are in a single x or y direction.
• Try to surround the print area with control points rather than lining them up.

Good distribution improves rotational and translational stability.

3. Compare Error Values Point-by-Point

• After recording points, review individual control point error values.
• Look for outliers that are significantly higher than the rest.
  • Understand the difference (delta) values associated with that point to understand if the high value is X&Y or Z related.
• A single bad point can distort the entire fit.

If one point stands out, it is often incorrect—even if it looks reasonable in the field.

4. Remove and Re-record Suspect Points

• Delete the control point with the highest error.
• Re-record it carefully, ensuring:
  • The reflector is centered precisely
  • The surface is clean and clearly marked
  • The laser tracker has a clean line of sight
• Recheck station information after re-recording.

If the error remains high, review with your team and consider excluding that point from the station.

5. Verify Elevation Consistency

• Confirm all control points used for stationing are at the same elevation.
• Do not mix slab, curb, wall, or column control points unless explicitly planned.
• Mixed elevations introduce tilt that cannot be corrected in software.

6. Re-evaluate Survey Quality When Needed

• If multiple points show high error, the issue may be the survey—not the robot.
• Ask whether control points were:
  • Shot with a bi-pod prism
  • Re-shot and verified after marking
  • Placed on uneven or dirty surfaces

In these cases, re-surveying or adding additional verified points is required.

Best Practices

• Use more control points than you think you need. Three is a minimum, not a goal.
• Trust patterns, not single numbers when reviewing error and difference (delta) values.
• Treat high differences (deltas) as warnings, not software problems.
• Keep control points clean, sharp, and well-marked on site.
• Coordinate early with survey teams on control placement and expectations.

A strong control network makes layout predictable, repeatable, and defensible across trades.