For every measurement 4D's 4Sight Analysis Software calculates the peak-to-valley height (PV), which is the difference between the highest point and lowest point in a measurement. PV gives a very general, though limited sense of surface roughness. Since it relies upon only two points in the entire dataset it is highly susceptible to spikes, noise, diffraction, edge effects and missing data.
4Sight also includes two additional statistics, PVq and PVr. These parameters are computed using nearly all of the measured data points and will give much more reliable and repeatable peak-to-valley results. You can choose whether or not to calculate these statistics in the Analysis Options > Statistics tab.
Q Peak-Valley (PVq) disregards the highest and lowest pixels and only considers the remaining Q Percent of pixels. To calculate PVq, 4Sight generates a histogram of surface heights, then determines the narrowest band of the histogram that contains the Q Percent of pixels (Q must be >50). The result will be displayed in the Dataset Statistics table found on many 4Sight screens.
Robust Peak-Valley (PVr), originally proposed by Dr. Chris Evans of the University of North Carolina Charlotte (and formerly of NIST), provides a more robust measure of surface shape. It is calculated from the peak-to-valley of a 35-term Zernike fit to the measured data plus 3*RMS of the residual (the residual is the dataset minus the 35-term fit). The result will again be displayed in the Dataset Statistics table found throughout 4Sight.
Click here for more information on 4Sight software.
4Sight also includes two additional statistics, PVq and PVr. These parameters are computed using nearly all of the measured data points and will give much more reliable and repeatable peak-to-valley results. You can choose whether or not to calculate these statistics in the Analysis Options > Statistics tab.
Choose to calculate PVq and PVr in the 4Sight analysis software Statistics options tab.
Q Peak-Valley (PVq) disregards the highest and lowest pixels and only considers the remaining Q Percent of pixels. To calculate PVq, 4Sight generates a histogram of surface heights, then determines the narrowest band of the histogram that contains the Q Percent of pixels (Q must be >50). The result will be displayed in the Dataset Statistics table found on many 4Sight screens.
Robust Peak-Valley (PVr), originally proposed by Dr. Chris Evans of the University of North Carolina Charlotte (and formerly of NIST), provides a more robust measure of surface shape. It is calculated from the peak-to-valley of a 35-term Zernike fit to the measured data plus 3*RMS of the residual (the residual is the dataset minus the 35-term fit). The result will again be displayed in the Dataset Statistics table found throughout 4Sight.
Click here for more information on 4Sight software.
