21-09-2013, 04:56 PM
Filter a curve with one of the mirror filter tools in HyperGraph, HyperView
Topic details:
Frequently, a filtered data curve's start and end data points might not match well with the original curve's
corresponding points. However, HyperGraph (HG), HyperView (HV) and MotionView (MV) have mirror
filter tools found in the Vehicle Safety Tools to correct this situation.
How the mirror filter tools in HG, HV and MV work
Figure 1 below can help you visualize what happens. First, a mirror filter tool reflects the unfiltered curve
about two vertical lines, one at the curve's start point and the other at the curve’s end point. It then
combines the three curves. There are now data points on both sides of the original curve's start and end
points. Next, the tool filters the elongated curve. It uses the reflected data when filtering the curve. Lastly,
the tool trims the curve at the same vertical lines the original curve was reflected about. This is all done
behind the scenes; you do not see the reflected curves or the elongated curve in the HG, HV or MV
window. What you see is the resulting filtered curve with start and end points in close proximity to the
original curve's corresponding points.
How a filter algorithm works without a mirror tool
The unfiltered curve in Figure 2 below has 150 data points. It was filtered in HG (or HV or MV) using a
filter algorithm without a mirror tool. From the Filter... button in the Define Curves panel, the SAE filter
class 60 was used to filter the curve. Filtering involves using data points before and after a point of
interest. For point 50, the algorithm uses points 45 through 55 to calculate the filter point. For point 150,
however, the algorithm does not have any points beyond point 150 to work with. It only has points 145
through 150. This causes the filtered curve's end to tend sharply toward zero and results in the filtered
curve's end not matching well with the original curve's end.