To obtain the data needed to calibrate a camera, six or more photographs taken from different angles of a the target pattern are needed. There are two types of camera calibration (see Calibration Type): Single Sheet method works with a specific Calibration Grid; Multi-sheet method works with a series of Target Sheets.
We recommend using 8 to 12 photographs of the target pattern taken in the positions described below. The images show a Single Sheet calibration grid, but the photography concepts apply to both Single Sheet and Multi-sheet.
Additional photographs can be added if desired. The calibration can have trouble with a large number of photographs (over 12) when the lens is wide angle and has high distortion.
It is very important to note that the target pattern should fill as much of the photograph as possible.
For Single Sheet Calibration, the four control point locations must all appear in each photograph and must not be cut off by the edge of the photograph (the four control points are the coded targets, i.e. the dots with partial rings around them).
In the figures below (starting with Position 1 - normal) the left pictures show the image taken by the camera and the right pictures shows a 3D view of the camera position and the projected calibration grid. Note that the control points come close to the edge of the image, but are never cut off.
Important note: Ensure you do not cut off the control points or coded target rings in the photos. Ensure the grid fills as much of the frame as you can. Ensure you have at least two photos with roll angles of 90 degrees (portrait orientation) - we recommend four rolled (90 degree) photos.
The following figures depict a suitable 8 photo calibration photo set. There are four camera positions and one landscape and one portrait shot at each position. The first figures show 3D views of the camera positions (first from the top and then a perspective view). For the 12 photo case, an extra 90 roll in the opposite direction is added at each position.