Geometric Calibration (deprecated)

Supported Systems for Calibration

Current Documentation
View previous documentation
View legacy documentation
All documentation versions


Deprecated in Current Release

Requirements Software operation Defining Calibration Tasks Definitions and Theory

Supported Systems

Supported Targets

Required Evidence

Test Setup

Calibration Procedure

User Interface

Use in Imatest IT

Module settings

Module outputs

Defining a Device

Defining Distortion

Defining the System of Devices

Defining the Target

Defining a Test Capture

Defining a Test Image

Homogenous Coordinates

Projective Camera Model

Multi-Camera Systems

Distortion Models

Coordinate Systems

Rotations and Translations


 

Currently, Geometric Calibration in Imatest requires some assumptions about, and constraints on, the camera systems it supports.

While these constraints are relatively loose (most cameras and multi-camera setups will meet them), it is worth checking to make sure your system fits within the class of devices Imatest can calibrate.

 

Individual cameras

Central Projection + Radial Distortion

Imatest currently supports estimation only of the parameters of a central projection camera model, plus the addition of radial distortion. “Central projection camera” is also known as a “pinhole camera” or “perspective camera”. Fortunately, most classes of cameras can be very well described by this model.

The most common exception to this is the set of devices with >180° field of view. (In practice, calibrating anything in the range of 150° or greater is extremely challenging.)

Line-scan or push-broom imaging devices are somewhat supported in that they can be described by a type of projective transformation, though Imatest does not make any special considerations for these imaging models. 

 

Fixed settings

Any operation on the camera that affects one of the measured parameters invalidates the measured calibration. The most common such operation is zooming, which changes the focal length of a camera. Not only will this obviously change the f parameter estimation, but also it will typically change the distortion function as well.

If a camera design allows variation in the parameters of geometric calibration, it will need to be tested at each setting.

 

Multi-camera systems

Calibrating a multi-camera system with Imatest requires that each individual camera follow the above model, as well as a few further constraints. Note that these requirements hold for systems with two, three, or even more cameras. 

 

Overlapping field of view

Imatest can only determine the positioning of devices relative to one another if it can determine common points on the target viewed by each. The views need not necessarily be extremely similar, and indeed this is rarely the case, but they do need to overlap where the target is.

 

Rigid positioning

Imatest presumes the cameras in a multi-cam system are always in the same fixed positioning- the cameras cannot rotate or move relative to each other. 

If the system allows camera positioning changes, calibration will need to be performed at each position (or alternative can be used to verify each position).