B4J Question [Solved] Build Map Polygon From Lat/Lon List

Sub chart_chartitemclicked(Message As String)
    
    Dim sb As ABMSideBar = page.GetSideBar("SideBar")
    Dim cn As ABMContainer =  sb.Content.Component("cnt1")
    Dim us As ABMCheckbox = cn.Component("btnshowus")
    DateTime.TimeFormat = "HH:mm:ss"
    ListFindOther.Initialize
    
    Dim mark As List
    mark.Initialize
    
     Dim mes As String = Message
    
'    Log(" chart clicked "&Message)
    Log(" ECM File SIze: "&ListECM.Size)
    
    Dim idx As Int = Message.IndexOf("row:")
'    Log(" row at: "&idx)
    mes = mes.Replace("row:","")
    Dim idx As Int = mes.IndexOf(",")
    Dim val As String =""
    If idx > 0 Then
         val  = mes.SubString2(1, idx)
        Log(" rec to get: "&val)
    Else
        Log(" no index > 0")   
    End If
    If IsNumber(val) Then
        Dim val0 As Int = val - 60 '20
        If val0 < 0 Then
            val0 = 1
        End If
        Dim val1 As Int = val + 60 '20
        If val1 > ListECM.Size Then
            val1 = ListECM.Size
        End If
        
        gm1.RemoveMarkers
        gm1.RemovePolygons
        
        Log(" Number of select recs: "&(val1-val0) )
        Dim xpp As Map
        xpp.Initialize
        Dim xpp As Map = ListECM.Get(0)
'        Dim tlt As Double = xpp.Get("501") '+ 0.0009
        Dim tln As Double = xpp.Get("502") ' - 0.0005
        
        For i = val0 To val1         

            Dim mpp As Map = ListECM.Get(i)

            ListFindOther.Add(mpp)
            
            Dim lt As Double = mpp.Get("501") '+ 0.0009
            Dim ln As Double = mpp.Get("502")  + 0.0005
            
            If ln < tln Then
                Log("IF ln: "&ln&"  tln: "&tln)
            Else
                Log("else ln: "&ln&"  tln: "&tln)
                Dim tln As Double = mpp.Get("502")'  - 0.0005
                    
            End If

            If (i = val1) Then
                mark.Add(lt)
                If ln < tln Then
                    Dim temp As Double
                    temp = (tln - ln) + .005
                    mark.Add(tln - (temp))
                  
                   Log("Subtracting: "&ln&"  tln: "&tln)
                Else
                    Log("Adding "&ln&"  tln: "&tln)
                    
                    mark.Add(tln + (0.305))
                End If
            Else
                mark.Add(lt)
                mark.Add(ln)
            End If
            
            Dim lat As String = mpp.Get("501")
            Dim lon As String = mpp.Get("502")
            Dim sp As String = mpp.GetDefault("2",0)
            Dim tm As String = mpp.GetDefault("1",0)
            Dim rp As String = mpp.GetDefault("4",0)
            
            If us.State Then
                sp = NumberFormat2(sp * 0.62137 ,1,1,1,False)
            End If
            Dim dt As String = DateTime.Time(tm)
            
            Dim  legend As String = " {B} Time: "&"   "&dt&"  {BR}"
            legend = legend&" Speed: "&"   "&sp&"  {BR}"
            legend = legend&" RPM: "&"   "&rp&" {/B} {BR}"

            If i = val Then
                gm1.AddMarker( "mk"&i,lat,lon, ABM.COLOR_RED ,"Speed: "&sp&"    Time: "&"  "&dt&"  ", legend)
            Else
                gm1.AddMarker( "mk"&i,lat,lon, ABM.COLOR_Blue ,"Speed: "&sp&"    Time: "&"  "&dt&"  ",legend)
            End If   
        Next

        
        gm1.SetLocation( lat,lon)
        gm1.Refresh
            
    End If
    
    gm1.AddPolygon( "p1" , mark   , ABM.COLOR_DEEPORANGE, ABM.INTENSITY_NORMAL,  1.0,  5, ABM.COLOR_CYAN, ABM.INTENSITY_NORMAL,  0.3)

End Sub

'assume GPS track points are in arrays Lon() and Lat()

MinLon = Lon(0)
MaxLon = Lon(0)
MinLat = Lat(0)
MaxLat = Lat(0)

For I = 1 To NumTrackPoints - 1    'first point (array element 0) already done
    If Lon(I) < MinLon Then
        MinLon = Lon(I)
    ElseIf Lon(I) > MaxLon Then
        MaxLon = Lon(I)
    End If

    If Lat(I) < MinLat Then
        MinLat = Lat(I)
    ElseIf Lat(I) > MaxLat Then
        MaxLat = Lat(I)
    End If
Next I

'allow a bit extra in each direction to handle GPS wander etc:

LatBuffer = (50 / 40000000) * 360    '50 metres = 0.00045 degrees latitude (planet earth circumference is nominally 40,000 km = 40,000,000 m)
LonBuffer = LatBuffer / Cos(68 degrees)    '50 metres = 0.00120 degrees longitude (scale varies with latitude)
'probably better as: LonBuffer = LatBuffer / Cos((MinLat + MaxLat) / 2) for use at other latitudes

'bounding rectangle polygon is now the four points:

'(MinLon - LonBuffer, MinLat - LatBuffer) to
'(MinLon - LonBuffer, MaxLat + LatBuffer) to
'(MaxLon + LonBuffer, MaxLat + LatBuffer) to
'(MaxLon + LonBuffer, MinLat - LatBuffer) to
'(MinLon - LonBuffer, MinLat - LatBuffer) starting point again, if needed to close polygon