Calibration method for survey instrument and system for calibrating a survey instrument

System for calibrating a camera of a computer vision system, the camera comprising an image sensor and a diffractive aperture arranged for projecting incoming light onto the image sensor, the system comprising:

• a plurality of targets to be observed by the camera;
• a mounting device for mounting the camera, such that the plurality of targets are in a field of view of the camera when the camera is mounted on the mounting device, the mounting device enabling rotation of the camera between a first rotational position and a second rotational position with respect to the plurality of targets;
• and
• one or more processors configured to:
• (b) provide a camera model representing a mathematical model of a camera;
• (c) record a first image of the plurality of targets with the camera in the first rotational position;
• (d) determine a first set of calculated observation angles from the first image using the camera model, the first set of calculated observation angles comprising a first calculated observation angle of each target with respect to the camera;
• (e) record a second image of the plurality of targets with the camera in a second
• rotational position;
• (f) determine a second set of calculated observation angles from the second image using the camera model, the second set of calculated observation angles comprising a second calculated observation angle of each target with respect to the camera;
• (g) determine a function or plot based on the first and/or second set of calculated observation angles and a set of differential angles, the differential angles representing a difference between the first and second calculated observation angles for each target;
• (h) determine camera model errors from the function;
• (i) compare the camera model errors to a predetermined limit;
• (j) if the camera model errors are lower than the limit, determine the camera model as being acceptable;
• (k) if the camera model errors are not lower than the limit, calculate an updated camera model based on the camera model errors, and repeat steps d), f), g), h), i) and j) or k) based on the updated camera model.

A computer program product comprising instructions which, when executed by a computer, causes the computer to perform the steps of:

• (b) providing a camera model representing a mathematical model of a camera comprising an image sensor and a diffractive aperture arranged for projecting incoming light onto the image sensor;
• (d) from a first image of a plurality of targets, recorded with the camera in a first rotational position with respect to the targets, determining a first set of calculated observation angles from the first image using the camera model, the first set of calculated observation angles comprising a first calculated observation angle of each target with respect to the camera;
• (f) from a second image of the plurality of targets with the camera in the second rotational position, determining a second set of calculated observation angles from the second image using the camera model, the second set of calculated observation angles comprising a second calculated observation angle of each target with respect to the camera;
• (g) determining a function based on the first and/or second set of calculated observation angles and a set of differential angles, the differential angles representing a difference between the first and second calculated observation angles for each target;
• (h) determining camera model errors from the function;
• (i) comparing the camera model errors to a predetermined limit;
• (j) if the camera model errors are lower than the limit, determining the camera model as being acceptable;
• (k) if the camera model errors are not lower than the limit, calculating an updated camera model based on the camera model errors, and repeating steps d), f), g), h), i) and j) or k) based on the updated camera model.