Overview

Control points (also called surveyed points, datum points, or simply "control") are fixed reference marks on a jobsite with known coordinates. They tie the digital layout file to the real-world building so the FieldPrinter prints every line in the correct position and at true scale.

This article explains what control points are, why Dusty needs them, the types Dusty can use, how Dusty best-fits your layout to them, and the file formats Dusty accepts. It's written for VDC teams, surveyors, and field crews.

What Is a Control Point?

A control point is a physical marking with known X, Y, and Z coordinates (surveyors often call these Easting, Northing, and Elevation). A set of control points is called a control network.

Control points do three things:

• Give the laser tracker and the FieldPrinter a way to know exactly where they are on the slab.
• Anchor the digital layout file to the real-world jobsite.
• Give every trade a shared reference, so walls, sleeves, embeds, and equipment all align to the same system.

Think of control points as permanent measuring-tape zeroes that everyone on the project agrees on. They are set by a surveyor or layout team, they don't move during construction, and every trade references the same points.

Why Dusty Needs Control Points

Construction drawings live in a digital coordinate system; jobsites live in the physical world. Control points are the shared anchors that exist in both places — in the AutoCAD or Revit file, and physically on the slab, walls, or columns.

Dusty uses a laser tracker to take measurements from point to point. During setup ("stationing"), the tracker records the control points, and Dusty aligns the layout to them. The robot doesn't guess its position — it calculates it from the control network.

Because the tracker needs a clear line of sight, it may need to be re-stationed as the robot moves around columns, walls, materials, or other obstructions. For each station, the tracker must be able to see at least three control points.

How Best-Fit Alignment Works

The CAD file and the laser tracker each work in their own coordinate system. The Dusty App applies rotations and translations to bring the tracker's coordinates into alignment with the CAD coordinates. The layout is never scaled — it always keeps its true dimensions, so the printed layout is always produced at a true 1:1 scale regardless of small or big errors in the control points.

Dusty aligns the two sets of points using a method called least squares best-fit:

1. Find the centroid (center) of the recorded points and of the file points.
2. Shift the recorded points to align the centroids.
3. Rotate the recorded points until the differences between the file points and the measured points are as small as possible (least squares).

The leftover differences are the error values and difference values shown in the Dusty App. Because best-fit averages across all the points you record, recording more than the minimum improves accuracy and reduces the impact of any single point that is slightly off. This is also why you should not nudge the reflector off a marked point to make a number look better — it hides bad control and makes that point unusable later.

Types of Control Points

Horizontal control points

Most control points are marked on flat, horizontal surfaces. The reflector sits on a control point target placed over the mark. Common compatible types:

Control point type	Reflector tooling needed	Notes
Intersection of grid-line offsets	Control point target	Accurate if surveyed
Point mark on floor	Control point target	Accurate if surveyed
Arrow mark on floor	Control point target	Accurate if surveyed
Drift nest on column	Drift nest	Accurate if surveyed
Target on wall	Drift nest or vertical control target	Accurate if surveyed
Hole	Pin nest	Accurate if surveyed

Not compatible with the FieldPrint platform: survey pins and survey stakes — there is no reflector nest for these.

Not recommended: marks on unstable or small surfaces (the surface should be at least 3" across so the target rests stably), and thick cross marks (hard to place the reflector precisely, which causes inconsistency after re-stationing).

Vertical control points

Control points can also be placed on walls or columns instead of the floor — common in data centers and manufacturing/distribution plants. Because the laser tracker measures to the center of the reflector sphere, vertical control requires a small offset (about 1-1/4") to be applied so the coordinates line up. Dusty offers a purpose-built vertical control target with the offset built in.

For the full workflow, see How to Use Vertical Control Points for Accurate Layout.

When you don't have surveyed control

Dusty doesn't require a specific survey instrument or brand, and it can work on imperfect jobsites that don't have clean surveyed control — using tools like Create Control at Reflector, Persistent Control, and Corner Control. See What Is Flexible Control? Stationing Tools for Imperfect Jobsites.

Control Point File Formats

Dusty accepts control points in two ways:

1. CSV file (most common)

Control points are delivered as a CSV file uploaded to the Dusty Portal. The format is flexible on header wording:

• Minimum 4 columns: a point-name column, plus X, Y, and Z coordinate columns. A description column is optional.
• Header matching (case-insensitive, spaces and a "(ft)" suffix ignored):
  • Point name — header contains point or name (e.g., Point Name, Point, Name)
  • X — header contains x or east, or is exactly e
  • Y — header contains y or north, or is exactly n
  • Z — header contains z
  • Description (optional) — header contains desc
• Column order can be X, Y, Z or Y, X, Z.
• Coordinates must be plain numbers (no comma thousands separators, no text like "N/A"). Units default to feet on upload and can be changed to inches or meters in the import dialog.
• Coordinate system must match the layout file being published to the Dusty Portal.

2. Marked in the DWG file

Control locations can be indicated in the DWG using crosshair linework showing the intended X/Y intersections. These are used as a field reference to create the control points on-site with the iPad; the DWG geometry itself is not read directly as control input. Coordinates can also be exported from AutoCAD to a CSV using Dusty's LSP export tool or AutoCAD Data Extraction.

How Many Control Points You Need

Dusty requires a minimum of 3 non-collinear control points per station (they cannot fall in a straight line, and cannot form the answer with fewer than 3). More than the minimum is strongly recommended — additional points give best-fit more samples of the jobsite, improve accuracy, keep the layout consistent between stations, and protect you if one point is blocked or covered. Spread the points out so they surround the print area, and include points from previous setups when you re-station.

Related Articles

• What Is Flexible Control? Stationing Tools for Imperfect Jobsites
• How to Use Vertical Control Points for Accurate Layout

Good control is the foundation of accurate layout. Dusty makes that accuracy visible and measurable — but it starts with solid control points.