I am trying to draw a bus route as a simple sequence of lines. Nothing special. But instead of lines, I get wedges. Initially, I was fine with this, because the wedge sortings are similar to arrows and are always facing the second point. But now I want to improve the look, and wedges are becoming a big problem.
My suspicion is something like a floating-point problem due to a graphical conversion (lat / lons are cast, and the conversion turns them into x / y on a bitmap [assuming lat / lon is Euclidean, accurate enough for my purposes] , therefore scaling by several orders of magnitude).
Screenshot:
It actually looks like the line was divided into two triangles, but only one of them was drawn.
Corresponding code (note: the drawing is executed asynchronously, so I am creating a bitmap):
'-- Creating the transform --' Dim bitmap = New Bitmap(Math.Max(1, PictureBox1.Width), Math.Max(1, PictureBox1.Height)) Dim g = Graphics.FromImage(bitmap) g.TranslateTransform(0, bitmap.Height) g.ScaleTransform(1, -1) g.ScaleTransform(CSng(bitmap.Width) / (maxLon - minLon), CSng(bitmap.Height) / (maxLat - minLat)) g.TranslateTransform(-minLon, -minLat) '-- Drawing the lines (in a method called asynchronously) --' using pen = New Pen(Brushes.Black, 0.0001) Dim shapes = busData.TripsInGroup(tripGroup.Value). Select(Function(e) e.Shape). Distinct() For Each shape In shapes For i = 0 To shape.Points.Count - 2 Dim e1 = shape.Points(i) Dim e2 = shape.Points(i + 1) Dim p1 = New PointF(CSng(e1.Longitude), CSng(e1.Latitude)) Dim p2 = New PointF(CSng(e2.Longitude), CSng(e2.Latitude)) g.DrawLine(pen, p1, p2) Next Next
Example values:
cenLat = 44.657176 cenLon = -63.549471 spnLat = 0.071921 spnLon = 0.179729 minLat = cenLat - spnLat / 2 maxLat = cenLat + spnLat / 2 minLon = cenLon - spnLon / 2 maxLon = cenLon + spnLon / 2 shpts = {(Lat: 44.6518683235, Lon: -63.5930836628), (Lat: 44.6512537117, Lon: -63.5927528307), (Lat: 44.6508013753, Lon: -63.5924572976), (Lat: 44.6503312812, Lon: -63.5921923044), (Lat: 44.6503312812, Lon: -63.5921923044), (Lat: 44.6502137576, Lon: -63.5921260568), (Lat: 44.6495810455, Lon: -63.5917829189), (Lat: 44.648893839, Lon: -63.5913776026), (Lat: 44.6485468163, Lon: -63.5911976944), (Lat: 44.6485468163, Lon: -63.5911976944), (Lat: 44.6475084762, Lon: -63.5906617219), (Lat: 44.6475084762, Lon: -63.5906617219)}
Notes and discoveries:
- Using DrawLines instead of DrawLine solves the problem (but why?)
- Increasing the thickness of the pen makes the problem go away (but the lines are too thick)
- Zooming out (enlarging the lat / lon viewport) makes the problem go away in the end (but I want to zoom in!).