Display Calibration

Calibration aligns WATCHOUT's rendered output to the physical display surface. It covers projector alignment for 3D mapping, camera-based calibration over NDI® streams, and integration with external calibration systems through the HTTP API.

NDI Calibration Stream

For camera-based calibration workflows, each GPU display can be assigned an NDI Calibration Stream in the Calibration section of Device Properties. This is the name of an NDI® video stream that a camera-based alignment system uses to deliver test patterns to the display during calibration.

Setup:

1. Add a variable named displaycalibration to the show — see Variables and Inputs. The HTTP input that switches the display into and out of calibration mode only routes values to variables that already exist; without this variable the trigger has no effect and no error is reported.
2. Select the GPU display in Device Properties and open the Calibration section.
3. Enter the NDI stream name in the Calibration Stream field. The name must match the NDI source the alignment system publishes on the network.

Runtime flow:

1. The alignment system sends displaycalibration = 1.0 to WATCHOUT over the HTTP input endpoint.
2. WATCHOUT switches the display from show content to the NDI Calibration Stream, so whatever the alignment system streams over NDI appears on the projector.
3. The alignment system drives a sequence of test patterns onto the stream, captures the projected result with its camera, computes geometric corrections, and writes the result (typically an MPCDI file) to disk.
4. The alignment system sends displaycalibration = 0.0 and the display returns to normal show output.

Projector Calibration (3D Mapping)

For 3D projector displays, WATCHOUT provides a dedicated calibration system that uses point correspondences to compute the projector's position, orientation, and lens parameters. This is essential for accurate projection mapping where content must align precisely to a physical 3D model.

End-to-End 3D Mapping Workflow

The full 3D mapping process follows four steps:

1. Position real — set up your projector(s) and the object(s) you want to project on in the real world.
2. Prepare virtual — create a matching virtual scene in Producer by adding and positioning 3D models and projectors to match the physical setup.
3. Calibrate — align the virtual scene to the real scene by placing and matching calibration points on the 3D model and the physical surface.
4. Play media — project media onto the surface of the object(s).

Calibration UI Reference

The calibration toolbar provides the following controls:

Virtual Points and Reality Points

The calibration process works with two sets of points:

• Virtual points are placed on the 3D model in the Stage view. They mark known locations on the surface where you want the projected image to land.
• Reality points are the matching positions on the projector's 2D output where those locations actually appear when projected.

The calibration solves for the projector's lens parameters — the Width / Distance ratio and lens shift — together with its position and orientation, so the virtual and reality points line up.

Calibration Workflow

1. Switch to Calibration mode — in the Stage toolbar, switch the projector view from View mode to Calibration mode. This enables the calibration point editing tools.
2. Place virtual points — using the point tools in the Stage view, add virtual points on the 3D model at clearly identifiable surface locations (corners, edges, landmarks). You can add, move, and remove points using the toolbar actions.
3. Place at least six points — the calibration algorithm requires a minimum of six virtual points before you can edit reality points. This minimum ensures the system has enough constraints to solve for all projector parameters. More points can be added to further constrain the mapping.

1. Edit reality points — once six or more virtual points exist, switch to reality-point editing. For each virtual point, adjust the corresponding reality point to match where that location actually appears on the projector's output. The Stage view shows both sets of points for comparison.

Select a reality point by left-clicking on it (or close to it). You can also navigate between reality points using W/A/S/D keys or the left stick on a compatible gamepad (Xbox controller). Once selected, move the point using the arrow keys or the right stick of a gamepad. The goal is to make each reality point project onto the same physical location as its corresponding virtual point.

1. Calibrate — trigger the calibration computation. The system solves for the projector parameters that best align the virtual and reality point pairs.

Continuous vs. Manual Calibration

The calibration toolbar provides two calibration behaviors:

• Continuous calibration — the system recalculates the projector parameters automatically every time you move a point. This provides real-time feedback as you adjust reality points, making it easier to converge on an accurate alignment.

• Manual calibration — the system only recalculates when you explicitly press the Calibrate button. Use this when you want to adjust multiple points before triggering a recalculation, or when continuous recalculation is distracting.

Calibration Accuracy

After calibration, WATCHOUT shows an Accuracy percentage — how well the solved projector aligns the virtual and reality points. 100% is a perfect fit; the value drops as the points fail to line up. It is derived from how far the reality points land from where the solved projector would place them.

If accuracy stays low, review the point placements and check for:

• Points that are nearly coplanar (insufficient 3D variation)
• Incorrectly matched virtual/reality pairs
• Physical obstructions or distortions not captured in the model

Reposition Action

The Reposition action moves all reality points to sit directly on top of their corresponding virtual points in the current projector view. This is useful as a reset or starting point before manual fine-tuning — it gives you a clean baseline where both point sets overlap, and you can then adjust individual reality points to account for real-world discrepancies.

Projector Parameter Locking

In Device Properties, the While calibrating section locks specific projector parameters so the calibration cannot change them:

• Lock Lens Shift — keeps the horizontal and vertical lens shift fixed. Use this when you know the lens shift from the projector's specification.
• Lock Width / Distance Ratio — keeps the Width / Distance ratio (the throw) fixed. Use this when the throw is precisely known from the lens data.

Locking parameters reduces the degrees of freedom in the calibration solve, which can improve accuracy when the locked values are known to be correct, but can also degrade results if the locked values are wrong.

External Calibration Triggers

WATCHOUT supports an external calibration trigger mechanism that allows third-party calibration systems to put displays into calibration mode via the HTTP API. This is used in automated calibration workflows where an external camera-based alignment tool needs WATCHOUT to display calibration patterns while the external system captures and processes the result.

The trigger works through the Operative's HTTP input endpoint:

• Endpoint: POST /v0/inputs on the Operative's external port
• Input key: displaycalibration
• Value: 1.0 to enter calibration mode, 0.0 to exit

A typical automated calibration sequence:

1. The external system sends displaycalibration = 1.0 to put WATCHOUT displays into calibration mode.
2. The external system runs its calibration process (projecting patterns, capturing camera images, computing corrections).
3. The external system copies the resulting calibration data (e.g., MPCDI files) to the expected location.
4. The external system sends displaycalibration = 0.0 to return WATCHOUT to normal operation.

This integration supports hardware trigger devices (such as Elgato Stream Deck) for operator-initiated recalibration in permanent installations.

NDI® is a registered trademark of Vizrt NDI AB.