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Below a typical calibration object is shown. When calibrating a stereo
vision system with two or more cameras the following procedure is followed:
- Create a common Field of View - FOV for all cameras
- 2D Calibrate each camera with
Calibrator
- Place the calibration object in the center of the FOV
- Locate six or more known points on the calibration object with
each camera
- Create one ExternalReference3D for each camera
- Populate each instance with the corresponding 2D and 3D coordinate
pairs
The result is a Scorpion 3D model, which maps points in 3D to a 2D
calibrated plane. This is used as input to other 3D tools.
Below seven points are located automatically using eight
LineFinders and seven
PointFromLines instances on a 3D calibration object. The blue dots
indicates the PointFromLines constructed corners.
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Setup
Coordinate System
Reference - Incoming 2D Reference system selection
Global Position - optional 3D offset
Tool - selects
GlobalPosition3D instance
Note: The globalPosition3D instance must be connected to
all cameras in a Stereo Vision setup
Axis size - defines the length of the 3D axis visualisation
Note: Setting the length can be used to describe
the actual 3D FOV
Points 1-18 - describes 3D to 2D conversion. There are three
pages, with points 1-6, 7-12 and 13-18. These can be used simultaneously or
separately, depending on the application.
Points
Active - activate/deactivate point
3D - real coordinates of the calibration object (X, Y, Z)
2D - screen points (X, Y)
Max deviation - indicates the point with maximum deviation - this is a
possible candidate for deactivation
Paste/Copy buttons - transfer a point from/to the
clipboard
Import points a-b - Instantly imports current tool values
as static values. See below under Imports.
Inactive points a-b - deactivate all points on the current
page
Active points a-b - activate all points on the current
page
Imports
You can set up tools to provide (2D) points to your calibration.
For example a blob tool, or a line intersection tool (as in the
sample picture above). When the tool has a correct value, you can
import the current value into your ExternalReference3D as a
static number.
Active - activate/deactivate import of this point (when
the Import button is clicked)
Tool - the tool providing the 2D point
Result - the point result from the selected tool
Import points a-b - Same as the import button under
Points
Inactive imports a-b - deactivate all imports on the
current page
Active imports a-b - activate all imports on the current
page
Hints
RMS value shall be in the same order of magnitude of
the pixel size.
Verify the consistency of the relative camera positions from several
ExternalReference3D when working with stereo-vision.
Visualisation
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Axes
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The established 3D coordinate system
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Results
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A11...A43 |
The 4x3 projection matrix from 3D to 2D coordinates |
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f |
focal-length |
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l, v_x, v_y, b1, b2 |
These are internal camera parameters resulting from decomposition of
the matrix A, in general not interesting to the user |
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T_x, T_y, T_z |
The position of the camera in relation to the object coordinate system |
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Dev |
A measure of decomposition error |
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Number of points |
3D calibration points used |
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RMS |
Projection accuracy, in object coordinates (usually mm) |
ExecuteCmd
support (see also
executeCmd)
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Command |
Parameters |
Return values |
Comments |
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Import |
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ok, None |
Complete import all 2D and 3D points |
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Import2D |
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ok, None |
Complete import all 2D points |
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Import3D |
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ok, None |
Complete import all 3D points |
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Import |
POINT=<n> |
ok,None |
Import a single point (1-18), if import is active
for that point. Fails if the tool's config dialog is
open. |
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Import |
PAGE=<n> |
ok,None |
Import points on page n (1-3). Only points
with import active are imported. If the tool's
config dialog is open, it is updated. |
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Compute |
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ok,None |
computes new referencesystem, normally followed due
to above commands |
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SaveCalib |
CAMERA=<0..n-1>
FILENAME=<value>
UPDATE=0/1 |
True/False |
Save 3D calibration to file. If CAMERA is omitted, configured camera
number will be used. If FILENAME is omitted, profile name and
version will be used. If UPDATE<>0, Profilename, version and camera
name will be updated due to 'Refresh' button in configuration
dialog. |
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LoadCalib |
FILENAME=<value>
CAMERA=<0..n.1> |
True/False |
Loads 3D calibration from given file. If CAMERA is omitted
configured camera number will be used. |
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NOTE: Import commands overrides calibration from file
option, changes to using origin Reference
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Example 1: Set 2D points from Python
t1 = GetTool(':1-3DRef') # get camera calibration object
# create 2D points from six PointFromLines tools
s1 = '('
for p in range(1,7):
s1 = s1+'(%.5f;%.5f)'%(GetValue('1-pnt'+str(p)+'.Point_x'),GetValue('1-pnt'+str(p)+'.Point_y'))
s1 = s1+')'
t1.setConfigValue('2Dpoints',s1)
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