The manual says that the distance between RD and the target should be 3.0 m. What is the accuracy required, or, can I have a distance of less or more?
The distance of 3.0 m refers to vertical targets such as those mounted on a wall in a training center:
As you can see in the image, the distance is measured from the front of the RD case to the front of the target.
If the target is tilt by 15° such as when mounted on a stand, then the distance is best measured from the lower front edge of the target and has got a reference value of 2.85 m. This is the same as 3 x the length of the RD case.
Now, regarding the accuracy we recommend ±5cm. You can try larger deviations and it will work if the following conditions are met:
- The images are still sharp. Especially when doing the chessboard calibration, both the upper and the lower chessboards need to appear sharp in the test images, not blurred.
- The whole target is seen by the cameras, especially if it’s a 122 cm target face. If RD is too close to the target, the observed area gets smaller.