Android Question Exponential smoothing code for 1D int array

RB Smissaert said:

Does anybody have code to smooth out a 1D int array holding satellite altitude data?
I would like to just pass the array and get an altered array (may have double values) back.

Click to expand...

Dim HistoryProportion As Double = 0.5    '0 (no history, only current value ie no smoothing) to 1 (all history, no current value) (ie too much of a good thing)

If NumAltitudes > 0 Then
    Dim Smoothed(NumAltitudes) As Double
    Smoothed(0) = Altitude(0)
    For I = 1 To NumAltitudes - 1
        Smoothed(I) = Smoothed(I - 1) * HistoryProportion + Altitude(I) * (1 - HistoryProportion)
    Next
End If

Dim HistoryWeight As Int = 1    '0 = no smoothing, larger values = more smoothing

If NumAltitudes > 0 Then
    Dim Smoothed(NumAltitudes) As Double
    Smoothed(0) = Altitude(0)
    For I = 1 To NumAltitudes - 1
        Smoothed(I) = (Smoothed(I - 1) * HistoryWeight + Altitude(I)) / (HistoryWeight + 1)
    Next
End If

RB Smissaert said:

Does anybody have code to smooth out a 1D int array holding satellite altitude data?
I would like to just pass the array and get an altered array (may have double values) back.

Click to expand...

Dim HistoryWeight As Int = 1    '0 = no smoothing, larger values = more smoothing
Dim HistoryWeightRounding As Int = (HistoryWeight + 1) / 2    'for rounding, assuming Int division truncates

If NumAltitudes > 0 Then
    Dim Smoothed(NumAltitudes) As Int
    Smoothed(0) = Altitude(0)
    For I = 1 To NumAltitudes - 1
        Smoothed(I) = (Smoothed(I - 1) * HistoryWeight + Altitude(I) + HistoryWeightRounding) / (HistoryWeight + 1)
    Next
End If

William Lancee said:

Here is a simple approach that works with any sequence of points.
A point has an x,y. Your y is the altitude. Your x = 0,1,2,3,4,5,... Or perhaps 'time'

The "feature" of this approach is that the resulting line is smooth and is not constrained to fit through any particular point - except start and end point.

https://www.b4x.com/android/forum/t...h-curved-line-to-a-sequence-of-points.143178/

You can also try various averaging techniques. A running average of 3 or 5 points, smooths points well depending how large outliers are.
new P(i) = [p(i-2) + p(i-1) + p(i) + p(i+1) + p(i+2)] / 5 At the boundaries just adjust that formula: p(0) = p(1)+ p(2) /2 etc.

By weighting each term, you can achieve good results, depending on the data.

Another common smoothing approach is the the use of cubic splines or Bezier curves.

If you are using this data where you have to communicate with others about your curves, you need to check the literature to see what acceptable techniques are being used for you kind of data. What methods are commonly used for smoothing altitude data? I googled and here are some suggestion, even an algorithm.

Click to expand...

Dim HistoryWeight As Int = 1    '0 = no smoothing, larger values = more smoothing

If NumAltitudes > 0 Then
    Dim Smoothed(NumAltitudes) As Double
    Smoothed(0) = Altitude(0)
    For I = 1 To NumAltitudes - 1
        Smoothed(I) = (Smoothed(I - 1) * HistoryWeight + Altitude(I)) / (HistoryWeight + 1)
    Next
End If