Vertical control points are surveyed reference points placed on walls and columns instead of the floor. They let the FieldPrinter station and print accurately on jobsites where floor control is impractical or where the surveyor works from vertical surfaces — common in data centers, distribution centers, and manufacturing plants.
The one thing that makes vertical control different from floor control: the laser tracker measures to the center of the reflector sphere, not to the marked point on the wall. Because the reflector sits a fixed distance off the wall, the surveyed coordinates must be shifted by that offset before printing. This guide explains how that offset works and how to apply it.
How Vertical Control Works
The FieldPrinter stations using a laser tracker and a 1-1/2" spherical reflector (SMR). Unlike a total station, which can measure directly to a wall surface, the laser tracker measures to the center of the reflector sphere.
Because of that geometry:
- If a 1-1/2" spherical reflector (SMR) and Dusty's vertical control target are used, the reflector's center sits a fixed distance — 1-1/4" — off the point marked on the wall.
- The surveyed control point coordinates must be shifted by that same 1-1/4", in the correct direction, so the data matches where the tracker actually measures.
If the offset is not applied, every vertical control point is off by 1-1/4", and the layout will not station correctly. Applying the offset is the core of the vertical control workflow — it is not optional.
Dusty's Vertical Control Target
To make this repeatable, Dusty provides a purpose-built, 3D-printed vertical control target (reflector nest):
- Holds the reflector in a repeatable, accurate position on the wall or column.
- Lightweight and low-cost.
- Built with the correct 1-1/4" offset, so the standoff distance is known and consistent for every point.
Using the same target for both the survey and FieldPrinter operation is what keeps the 1-1/4" offset consistent from point to point.
How to Apply the Offset
Apply the 1-1/4" offset one of two ways. Do this once, before printing — never both.
Option 1: Edit the CSV directly
Add or subtract 1-1/4" from the X and/or Y coordinate of each control point, depending on which way the reflector faces and how the layout's coordinate system is oriented.
Example: The CSV holds the coordinates of the points on the wall, but the reflector center is 1-1/4" off the wall in the Y direction. Add 1-1/4" to the Y coordinate of each point.
Option 2: Shift the points in CAD
Move the control points by 1-1/4" in your CAD file before exporting the CSV. This is often less error-prone than editing the CSV by hand. You can use Dusty's LSP commands, Autodesk Point Layout, or native AutoCAD commands (Insert Multiple Points, MOVE, and DATAEXTRACTION).
Placement and Recording
Vertical control points follow the same placement and stationing rules as floor control:
- Record 3 or more control points per station (minimum 3 non-collinear). More points improve best-fit accuracy and keep the layout consistent between stationings.
- Spread the points around the print area so they enclose what you're printing.
Selecting Control Points For Best Accuracy | |
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Scan control points that are far away.
Errors only cover the area between recorded control points. When your control points are spaced far apart, you can print accurately over a larger area - even if the shown error is higher than with closer points. |
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More recorded points is always better.
It is better to have five control points with an 1/16" station error than only three with smaller errors. The more control points you have, the more accurate your print alignment will be. |
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Record control points around your print area.
To make sure your control points are spaced out properly, set them up around the area that you plan to print. |
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Best Practices
- Place targets on stable, permanent surfaces — concrete walls or structural columns, not temporary or movable objects.
- Label and protect the targets so they stay usable and undisturbed for the whole project.
- Double-check the offset was applied correctly before printing. This is the most common source of error in vertical control.