3DCal is a process which ensures that the properties of a virtual projector such as its location, rotation and lens properties, match the ones of its physical twin.

In essence, the process is very simple. You need to select at least 6 pairs of matching points on the virtual projection object and the physical one. The points need to fulfill the following conditions:

  • The points should not be on the same plane. Even though the projection might look ok, the projector might not be placed correctly.

  • Try to pick non symmetrical points. If the points are entirely symmetrical the projector might not be placed correctly.

  • It helps if the points are spread across the entire projected part of the object.

When you select the pairs of points a value called Reprojection error is calculated. For maximum precision, this value should be kept below 1px.

Quick Guide to 3DCal

3DCal starts with getting a precise 3D model of your projection object into LightAct. In our case, we will use a 3D model of a curved wall.

Before initiating the 3DCal process, it is important to place the virtual projector roughly where the physical projector is relative to the object. You don’t need to be very precise.

Double click on the projector or right click on it and select Setup to enter its layout and 3DCal window.

Then click on the 3DCal tab.

In the window you will see 2 preview rectangles. On the left one, there is the view as seen from the virtual projector in the viewport and on the right is what is being output from the projector.

On the right hand side, there are a few buttons with which you can control the process:

Further down there are additional settings:

  • In the Output section, you can toggle whether the points get output to the output. After you’ve finished with the point selection process, you’ll want to disable this checkbox in order to evaluate the precision of the calibration.

  • Under Viewport, you can change the Render mode of the projected object.

  • Calibrate on change toggles whether a projector gets calibrated with every new point or movement of an existing one, or if it gets calibrated only when you press Calibrate button.

  • Snap to vertex toggles whether the point you click on a virtual model will always snap to the closest vertex in the 3D model.

  • Adjust projection points can improve your calibration by adjusting the projected points to a more accurate position, lowering the reprojection error. The max delta property indicates the range in which the points will be adjusted in.

  • In the Preferences section you can control the physical point selection cursor. For example, the background color and the color of the cursor, its thickness and so on.

  • In the Viewport section, you can toggle whether 3D helper spheres get rendered in the main Viewport showing the virtual points you selected.

  • In the Fallbacks section, you can save potential calibration solutions for your projector. This is a very powerful feature as it allows you to restore and toggle between different calibration solutions, compare them and fine tune them whenever you would like.

3D Calibration Process Overview

You can perform the 3DCal process in whichever sequence you want. For example:

  1. As a first step, it might be advisable to click the Store current orientation button, so that you can revert to it in case the calibration goes wrong and your projector is moved somewhere far away.

  2. First select all virtual points and then click on the physical points.

  3. First select all the physical points and then click the matching virtual ones

  4. Go one-by-one.

It doesn’t really matter which way you go, but in this quick guide, we will first click on 6 virtual points and then select matching physical ones.

Selecting virtual points

In the 3DCal tab, click on 6 points on the virtual 3D model on the left side of the window. For now, probably it is best to leave the Snap to vertex checkbox checked.

You might want to enable Draw helper spheres in the Viewport to see the selected points on the object itself.

Selecting projected points

Selection of projected points happens on the right part of the window. Please note, that before you can select the points, the projector needs to be properly mapped to an enabled physical output.

Click the points one by one and after you’ve clicked on the 6th one, the projector will get calibrated and moved to a new location. If the process was successful, the reprojection error will be below or close to 1.

Feel free to add more points or delete some of them by right clicking on them. You can also move points a bit in order to make the projection more precise.

Good to know: Use arrow keys to move the cursor by 1px to be more precise. You can also select one of the points and move it either with the mouse or by using arrow keys.

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