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10 Measurement Algorithms
All measurement algorithms use the same process to compute the altitude maps which
are displayed on the main screen at the end of a measurement. The choice of
algorithm depends on which numerical parameters best characterise your application
and what filtering is applied to the altitude map.
10.1
O-Rough algorithm
This algorithm has been specifically designed to apply band filtering, before computing
any roughness characteristics. Based onto ISO-16610 norm, user has got the
possibility to apply High pass (keep only high frequency
–
short waves-), Low pass
(keep only low frequency
–
large waves-) and band pass (keep only a range of
wavelength). Two bands can be defined independently, adjusting low limit, high limit,
or both in case of band filtering.
After the algorithm has applied filters, 4 characteristics are calculated following ISO-
25178 norm. They are Sa, RaX, RaY, RsM. User should refer to this norm to know
more about calculation formulae. Optimap3 is performing calculation using the whole
field of view from the Altitude topographic map. This map is given without filtering and
is also given for the two selected bands.
10.2
Altitude
The Optimap3 is also capable of filtering the raw altitude map with a series of band
pass filters to highlight specific features.
The altitude map is filtered using 7 bands, to produce 7 surfaces.
Band name
Low limit (mm)
High limit (mm)
A
0.1
0.3
B
0.3
1.0
C
1.0
3.0
D
3.0
10.0
E
10.0
30.0
LW
1.2
12.0
SW
0.3
1.2
The altitude map is filtered using a 2D Gaussian filter like that described in ISO-16610.
For each filtered surface, a Sa parameter is calculated following ISO-25178 norm
•
Arithmetical Mean Height (Sa)
is calculated using the filtered altitude map of
the measured area. It is reported in μm. It is defined as follows:
𝑆𝑎 =
1
𝐴 ∬
|𝑍(𝑥, 𝑦)|𝑑𝑥𝑑𝑦
𝐴
