fastest way to create a bitmap from a large List of items - vb.net

Question

I am currently creating a list of a class item
Public glstBeamsList As New List(Of BEAMLAYOUT)
Public Class BEAMLAYOUT
Public sourceLocation(2) As Double
Public pointEastingNorthingDepth As New List(Of Double())
End Class
This class list items can have up to 256 points in it with 3 items in the array.
my issue is that the glstBeamsList is continuously being added to and the routine I have reading thru the list to draw the points to a bitmap and display on screen takes a very long time once the list gets large.
here is the code I am using any help is appreciated.
Dim Eastlimit, WestLimit, NorthLimit, SouthLimit As Double
Eastlimit = dblSourceLocationEastings + (gintPlanWidth / 2)
WestLimit = dblSourceLocationEastings - (gintPlanWidth / 2)
NorthLimit = dblSourceLocationNorthings + (gintPlanHeight / 2)
SouthLimit = dblSourceLocationNorthings - (gintPlanHeight / 2)
For i = 0 To glstBeamsList.Count - 1
If glstBeamsList(i).sourceLocation(0) = 0 Or
glstBeamsList(i).sourceLocation(1) = 0 Then GoTo nextPoint
For ii = 0 To glstBeamsList(i).pointEastingNorthingDepth.Count - 1
Dim point() = glstBeamsList(i).pointEastingNorthingDepth(ii)
If point(0) < Eastlimit Then
If point(0) > WestLimit Then
If point(1) < NorthLimit Then
If point(1) > SouthLimit Then
Dim x, y As Double
If point(0) < glstBeamsList(i).sourceLocation(0) Then x = point(0) - glstBeamsList(i).sourceLocation(0)
If point(0) > glstBeamsList(i).sourceLocation(0) Then x = glstBeamsList(i).sourceLocation(0) - point(0)
If point(1) < glstBeamsList(i).sourceLocation(1) Then y = point(1) - glstBeamsList(i).sourceLocation(1)
If point(1) > glstBeamsList(i).sourceLocation(1) Then y = glstBeamsList(i).sourceLocation(1) - point(1)
Dim clrPointColor As New Color
Select Case point(2)
Case -10 To 0
clrPointColor = Color.Red
Case -20 To -11
clrPointColor = Color.Orange
Case -30 To -21
clrPointColor = Color.Yellow
Case -40 To -31
clrPointColor = Color.Green
Case -50 To -41
clrPointColor = Color.Blue
Case -60 To -51
clrPointColor = Color.Indigo
Case -70 To -61
clrPointColor = Color.Purple
Case -80 To -71
clrPointColor = Color.Violet
Case -90 To -81
clrPointColor = Color.Gray
Case -100 To -91
clrPointColor = Color.Black
Case -110 To -101
clrPointColor = Color.Red
End Select
Dim xLoc As Integer = ((gintPlanWidth / 2) + x) * gsngPlanScaleFactor
Dim yLoc As Integer = ((gintPlanHeight / 2) + y) * gsngPlanScaleFactor
If xLoc > 0 And xLoc < PicBox.Width Then
If yLoc > 0 And yLoc < PicBox.Height Then
ggfxPlanViewBitmap.SetPixel(xLoc, yLoc, clrPointColor)
End If
End If
End If
End If
End If
End If
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