SICK Ranger E

Chapter 5 Reference Manual
Ranger E/D
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Configuring Ranger E and D
In the case that the true light peak (the laser) is the first along the search order the correct
range value will be computed.
Center-of-gravity
Center-of-gravity (Cog) is another method of finding the impact position of the laser line in
a sensor column. With this method typical resolution of 1/16
th
of a pixel is achieved. The
Hi3D algorithm is based on calculations similar to Cog.
In the Center-of-gravity method a threshold is also used, but for removing background
information before the AD conversion. The sensor data above the threshold is digitized to a
5–8-bit representation, and the sensor data below the threshold is set to 0 as in the
ordinary thresholding. The center-of-gravity is then calculated through two sums:
Cog =
(x * f (x))
(f (x))
Where x is the sensor row and f(x) the digitized intensity level in the sensor data.
Figure 5.15 – Calculating the center-of-gravity
Median Filter
The Median filter calculates a median value on the binary data of 3-columns of the binary
image (actual column and its left and right neighbors) before the range algorithm is ap-
plied. This filter pre-process the binary image data used in the profile detection of the
Horizontal Threshold and Horizontal Max and Threshold components. The calculation does
not increase the time for the processing.
In cases when using two thresholds this filter is applied to both binary results independ-
ently, but with the same parameters.
If both median filter and morphological is used, the morphological filter is applied before
the median filter.
Morphology Filter
The morphology parameter is used for reducing noise in the sensor image before the laser
line is detected. It can be used with the Horizontal Threshold and Horizontal Max and
Threshold components.
Ideally the laser peak on the sensor is a smooth peak without any noise present. However,
due to different noise sources the peak may be affected by noise peaks. The morphology
filters are designed to reduce the effect of these noise peaks. If, when studying a Ranger
Intensity
Sensor ro
w
ROI start
ROI end
Threshold
Sensor ro
w
ROI start
ROI end
Intensity