Projector calibration with 3DCal

Projector calibration is a process which determines the properties of the projector. They are grouped into intrinsic and extrinsic properties. Intrinsic properties are lens shifts and lens distortion (although LightAct doesn’t use lens distortion at the moment for projection mapping). Extrinsic properties are location and rotation of the projector.

Overview of 3DCal process

3DCal is a process of matching 3D points on the surface of the virtual objects with 2D points in the projector-space. This process needs to be repeated for every projector.

The video above shows the entire process.

Everything is done in 3DCal tab of Projector window. There are 3 ways to open Projector window:

  1. by double-clicking on the projector in the Visualizer,
  2. by right-clicking on the projector in the Visualizer and selecting Projector setup or
  3. by clicking on Setup button in the View tab of projector properties

The image above shows the area where you should click Projected points (area 1) and the area where you can click Virtual points (area 2). The projector you are calibrating needs to mapped to a physical output and the output enabled. In order for the calibration to start you need at least 6 pairs of points.

You select the projected points not by looking at your computer screen but by looking at the physical projection object where, once you check Project points to output, you should see a crosshair. You can adjust the colors of the crosshairs in the Preferences section.

In Projector Controls section you can enable & disable overrides for other projectors, which will make it easier to calibrate the projector you are working on at the moment.

There are several checkbox on the right-hand side, so let’s go through all of them:

  • Calibrate on change: if checked, every new point or movement of an existing point will trigger a re-calibration of the projector. Uncheck if you need to move several points at the same time.
  • Snap to vertex: if checked LightAct will try to find the closest vertex on the 3D model. Useful if you want to click only on corners of the object.
  • Render virtual points in Visualizer: if checked you will be able to see all virtual points in the Visualizer. Useful if you are using Snap to vertex functionality, because sometimes the point can snap to a nearby vertex instead of where you wanted it to be. You can adjust the radius of the spheres in the Visualizer.
  • Project points to output: overrides the projector content and outputs background color with cross-hairs, so you can select projected points.

After calibration process is complete, please note the Reprojection error label on the right. It tells you the estimated precision of projector calibration and it should be as low as possible. Under 2 px is usually ok, but ideally you should get it under 1 px.

Setting up virtual projectors

Virtual projectors are digital representations of real projectors. They act as a camera in the Visualizer which means the content is already warped to the objects they see. If you went through the previous chapter you should already have a cube with a texture applied to it in the Visualizer. Now, what you can do is […]

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Applying content to objects

UV mapping tells a computer how to apply a texture to a 3D object. We’ll start this tutorial by importing an already mapped cube thus making the assumption that you know how to create a UV mapped cube in a 3D modeling software. We import a UV mapped object by pressing Ctrl+D (or by going […]

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Projection Mapping Overview

LightAct allows you to use 2 approaches to projection mapping. They are usually referred to as 2D projection mapping and 3D projection mapping. 3D projection mapping 3D projection mapping relies on accurate 3D models of all projection objects and using projectors as cameras into the virtual space. The setup process is as follows: import UV-mapped […]

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