Enhanced 3D Correction - Scanlab RTC 5 PC Interface Board Installation And Operation Manual

8.6.5 Enhanced 3D Correction

The image size of 3D scan systems – particularly those
without objectives or with non-telecentric F-Theta
objectives – depends on its distance to the scan
head's objective (i.e. from the Z coordinates). The
image field size typically gets stretched or squeezed
linearly with the Z value. Therefore, SCANLAB 3D
correction files include stretch correction factors to
compensate for this effect (see
Assumption: for any chosen non-zero Z plane, (X, Y)
will be the desired position and (X', Y') the measured
position. The corrections <StretchX> and
<StretchY> are then calculated as follows:
<StretchX> = (X–X')/Z
<StretchY> = (Y–Y')/Z
The measurement can be performed as often as
desired in an iterative procedure to obtain optimal
correction value settings. Each newly determined
correction value can simply be added to the prior
values for a total correction.
You can then use the load_stretch_table
to load the enhanced 3D correction onto the RTC
from an ASCII text file. This file must contain correc-
tions for a complete rectangular grid. The number of
gridlines and their spacings can be freely defined and
even differ in X and Y. If the absolute values of the
corrections exceed 0.03125, then they will be clipped
to this limit value. The corrections are bilinearly inter-
polated for data points within the specified grid and
linearly extrapolated for data points outside the grid.
After load_program_file, enhanced 3D correction is
inactive by default. It becomes active upon loading a
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valid table onto the RTC 5 board and can subse-
quently be deactivated by calling
using a null pointer instead of the filename.
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RTC 5 PC Interface Board
Rev. 1.9 e
8 Advanced Functions for Scan Head and Laser Control
The following rules apply to the text file:
• The file can contain one or several tables, even
• The 2D stretch correction table must begin with
• This is directly followed by a block of data points.
page 124).
• If several tables with the same number exist, then
• Reading of the text data terminates upon end of
• All characters to the right of a semicolon are
• The order of data points is up to you.
• The maximum length of a data line is 255
• A data line contains two position coordinates (in
command
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5
• <Xpos> <Ypos> <StretchX> <StretchY>
• If a data point reoccurs, then the most recently
• Empty lines or incomplete data lines are invalid
load_stretch_table
tables of other types.
the caption [StretchTable<No>], whereby <No>
corresponds to the number supplied with the
load_stretch_table command.
only data from the first encountered table will be
read. The others will be ignored.
file or upon a line containing a caption.
treated as comments and ignored.
characters.
bits, signed integers) and two correction values
(dimensionless, signed floating point numbers,
use the period (.) or comma as the decimal
separator), each separated by spaces or tabs:
read value will be used; the others will be
ignored.
and will be ignored.
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