2.5 Convergence and Seamless Projection

The calibration processes described in sections 2.3 Manual 2D Keystone Calibration and 2.4 Manual 3D Calibration involved a single Display and a single Projection Surface functioning as an autonomous pair. However, in many situations, multiple projectors will aim at the same Projection Surface. This might be done to create seamless video coverage over the surface of a large screen or over a surface that wraps around a tridimensional structure. Multiple video projectors can also be stacked and aimed at the same screen to increase its luminosity. Both cases imply small changes to the calibration procedures and are explained below.

2.5.1 Convergence

Convergence occurs when multiple projectors are stacked and are aiming at the same Projection Surface. Convergent calibrations can be tricky to achieve because the projected image will be blurred if the geometrical corrections applied to each Display are not perfect.
To successfully apply a convergent calibration, make sure to follow these guidelines:
  • Use the same 3D object as the Reference Object for all Displays (in this case, the video projectors aimed at the same surface).
  • The 3D object acting as a Screen should also be made visible for each of the Displays.
  • Displays should share Calibration Points. Sharing some of the same Calibration Points will ensure that the Displays are properly aligned. The two most common examples are:
  • In a situation where two video projectors are aimed at the same area on a wall, the same four Calibration Points corresponding to the Screen’s four corners should be used for both Displays.
  • In a situation where two video projectors are aimed at a tridimensional structure acting as a Screen, Calibration Points placed in the intersection of the video projectors’ beams should be shared by both Displays.
  • Press [D] on the keyboard or click on the gear icon button to access the 3D Scene module’s Settings menu and click on the [Display Grid] toggle if the Display Grid isn’t already activated. Once activated, the Display Grid will help you align Displays because the pattern it projects onto Screens exaggerates the blurriness generated by a bad calibration.

2.5.2 Seamless Projection

In stage productions that rely on video mapping, coverage is often intended to span seamlessly across large surfaces. In some cases, large surfaces call for a very high pixel count, which can only be achieved by using multiple video projectors. To create the illusion of a seamless video image on a large surface follow these guidelines:
  • Video projector beams should cover the whole Projection Surface.
  • The beams of contiguous video projectors should intersect to create overlapping projection areas. These overlapping projection areas should amount to 15% of a Display’s total projection area.
  • Intersecting video projectors should share Calibration Points in their shared projection area.
  • Press [D] on the keyboard or click on the gear icon button to access the 3D Scene module’s Settings menu and click on the [Display Grid] toggle if the Display Grid isn’t already activated. Once activated, the Display Grid will help you align Displays since the pattern it projects onto Screens exaggerates the blurriness generated by a bad calibration in the shared projection area.