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360VR Treatment of Super-Wide-Angle Fisheye Lenses
Super-wide-angle fisheye lenses, with a field of view exceeding 180 degrees, can only be calibrated using the random-dot method, because any flat lens grid necessarily covers only a small portion of the image.
If calibration data from the manufacturer is available, a SynthEyes script can generate a lens distortion image map to convert the images to 360VR format, where they can be solved. In addition to the possibility of creating your own 360VR cameras with a back-to-back pair of cameras and lenses (sometimes with a drone in between), these maps can also be used to get 3D solves of wide-angle still images to make quicker on-set surveys for regular non-360VR projects.
To do this, use the File/Import/360 VR/Generate VR Lens Map Importer in the 360 VR area. It reads a small file of data from the lens manufacturer, and produces a lens distortion map that converts images to 360 VR format. The initial example for this is Entaniya super-wide- angle lenses (220, 250, and 280 degrees), which cannot be calibrated with typical lens grids.
The input file consists of multiple lines, each an incoming ray angle and the resulting image-plane radius. For example, the 250 degree 3mm lens data starts out
# Entaniya 250 deg 3.0mm --- comment line
0 | 0 |
|
5 | 0.2648 |
|
10 | 0.5295 |
|
15 | 0.7939 |
|
20 | 1.0579 |
|
25 | 1.3214 |
|
... |
|
This data is simply read from the Entaniya datasheet.
The importer requires a fair number of inputs that describe the camera that the lens is mounted on, such as the sensor size and resolution, which can generally be obtained from the lens manufacturer. It does require the lens center position, which is unique to each specific camera (even otherwise identical units). You can measure that with the Vignette-Based Lens Center Measurement procedure, for example.
When you later use the resulting map, you should use the Output tab of the image preprocessor to produce the final 360VR resolution, with an aspect ratio of 2.0.
©2023 Boris FX, Inc. — UNOFFICIAL — Converted from original PDF.