func (from TrackPoint) LatlongTimeBoxTo(to TrackPoint) geo.LatlongTimeBox {
return geo.LatlongTimeBox{
LatlongBox: from.Latlong.BoxTo(to.Latlong),
Start: from.TimestampUTC,
End: to.TimestampUTC,
HeadingDelta: geo.HeadingDelta(from.Heading, to.Heading),
Source: from.Source,
}
}
// If there are gaps in the track, this will interpolate between them.
// Will also fatten up the boxes, if they're too flat or too tall
func (t Track) AsContiguousBoxes() []geo.LatlongTimeBox {
minSize := 0.05 // In 'latlong' units; comes out something like ~3NM (~5 vertical)
maxSize := 0.10 // Boxes bigger than this get chopped into smaller bits
minWidth := 0.01 // Boxes are stretched until at least this wide/tall
boxes := []geo.LatlongTimeBox{}
iLast := 0
for i := 1; i < len(t); i++ {
// i is the point we're looking at; iLast is the point at the end of the previous box.
// should we create a box from i back to iLast ? multiple boxes ? Or skip to i+1 ?
dist := t[iLast].Latlong.LatlongDist(t[i].Latlong)
if dist > maxSize {
// Need to interpolate some boxes into this gap
nNeeded := int(dist/maxSize) + 1 // num boxes to create. int() rounds down
len := 1.0 / float64(nNeeded) // fraction of dist - size of each box
sTP, eTP := t[iLast], t[i]
for j := 0; j < nNeeded; j++ {
startFrac := len * float64(j)
endFrac := startFrac + len
sITP := sTP.InterpolateTo(eTP, startFrac)
eITP := sTP.InterpolateTo(eTP, endFrac)
box := sITP.TrackPoint.LatlongTimeBoxTo(eITP.TrackPoint)
box.I, box.J = iLast, i
box.Interpolated = true
box.RunLength = nNeeded
centroidHeading := sITP.Latlong.BearingTowards(box.Center())
box.CentroidHeadingDelta = geo.HeadingDelta(sITP.Heading, centroidHeading)
box.Debug = fmt.Sprintf(
" - src: %s\n"+
" - sTP: %s\n - eTP: %s\n - span: %.2f-%.2f\n"+
" - centroid: %.2f; sITP: %.2f; delta: %.2f\n"+
" - interp: %d points\n"+
" - sITP: %s\n - eITP: %s\n", t[0].Source, sTP, eTP, startFrac, endFrac,
centroidHeading, sITP.Heading, box.CentroidHeadingDelta,
nNeeded,
sITP, eITP)
boxes = append(boxes, box)
}
iLast = i
} else if dist > minSize {
// Grow an initial box with all the succeeding trackpoints
box := t[iLast].LatlongTimeBoxTo(t[iLast+1])
for j := iLast + 2; j <= i; j++ {
box.Enclose(t[j].Latlong, t[j].TimestampUTC)
}
box.I, box.J = iLast, i
centroidHeading := t[iLast].Latlong.BearingTowards(box.Center())
box.CentroidHeadingDelta = geo.HeadingDelta(t[iLast].Heading, centroidHeading)
boxes = append(boxes, box)
iLast = i
} else {
// This point is too close to the prev; let the loop iterate to the next one
}
}
// We don't want boxes that are too skinny, so we pad them out here.
for i, _ := range boxes {
boxes[i].EnsureMinSide(minWidth)
}
return boxes
}