given coordinate, find polyline width at that segment

[wang890]

i have a set of coordinates, not on the polyline. i want to find the polyline width where that coodinate intersects perpendicular to the polyline (shortest distance). without going through all the vertices.

i have a polyline with many segments with varying width, which are constant through the each segments (no taper width). need to read off the "instantaneous" width.

just 2dpoly or lwpoly not 3d.

i found this

http://through-the-interface.typepad.com/through_the_interface/2012/01/testing-whether-a-point-is-on...

not quite what i want.

thanks

[wang890]

i thought about going through the polyline vertices one at a time and then take my point and calculate distance. find the shortest distance from that and then record the index where that happens.

but i am afraid it may slow down my program. i have 1000 of these to run and if it goes through 1000 vertices could be slow. but i am gonna try it with my way first and hopefully someone has a better way.

[Jeff_M]

A polyline derives froma Curve, so it inherits the GetClosestPointTo() method. With the point you can get the parameter at the point which you can then use to GetStartWidthAt()

[wang890]

thanks jeff very helpful. not figured out yet but getting there.

where is the help file for all these rare functions? i think there is none. like roughly explains what the arguments you need to feed it do.

not just for this but generally for everything.

[wang890]

how do you get closest index giving a point?

doesn't have a "GetIndexAt" function

the getparameteratpoint returns a double? what is it which parameter does it return?

i need to get the index without going through the vertices as this will slow down my subassembly.

[Alexander.Rivilis · Accepted solution]

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@wang890 wrote:

the getparameteratpoint returns a double? what is it which parameter does it return?

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For Polyline parameter is number of vertex. For example parameter == 1 means second vertex, parameter = 2.5 means  middle between third and fourth vertex.

What are AcDbCurve/Curve Parameters? ObjectARX/.NET

Getting the Midpoint of each Polyline Segment using ObjectARX

[wang890]

seen.

i am off testing this now.

2.6 of a vertex lol.

[wang890]

works, here's the code

Dim oEmbankmentTypeTarget As WidthOffsetTarget

            Try
                oEmbankmentTypeTarget = oParamsOffsetTarget.Value("TargetHA1")

                Dim acDoc As Document = Application.DocumentManager.MdiActiveDocument
                Dim acCurDb As Database = acDoc.Database
                Using lock As DocumentLock = acDoc.LockDocument
                    Using acTrans As Transaction = acCurDb.TransactionManager.StartTransaction()
                        '' Open the Block table for read
                        Dim acBlkTbl As BlockTable
                        acBlkTbl = acTrans.GetObject(acCurDb.BlockTableId, OpenMode.ForRead)

                        '' Open the Block table record Model space for write
                        Dim acBlkTblRec As BlockTableRecord
                        acBlkTblRec = CType(acTrans.GetObject(acBlkTbl(BlockTableRecord.ModelSpace), _
                                                        OpenMode.ForWrite), BlockTableRecord)

                        Dim obj As DBObject = acTrans.GetObject(oEmbankmentTypeTarget.TargetId, OpenMode.ForWrite)

                        If TypeOf obj Is Polyline Then
                            Dim oPoly2dOrig As Polyline = CType(obj, Polyline)


                            'get the index where the current station is closest to
                            Dim x, y, z As Double
                            corridorState.SoeToXyz(corridorState.CurrentAlignmentId, corridorState.CurrentStation, 0, 0, x, y, z)
                            Dim oPt3D_CL As New Point3d(x, y, z)

                            'get vertex index (fraction)
                            Dim dVertex As Double = oPoly2dOrig.GetParameterAtPoint(oPoly2dOrig.GetClosestPointTo(oPt3D_CL, True))

                            'get polyline width
                            dSegmentWidth = oPoly2dOrig.GetStartWidthAt(Truncate(dVertex))

                        End If

                    End Using

                End Using

[Alexander.Rivilis]

IMHO method Truncate should be replaced with method Round.

[wang890]

no, have to round down.

say point 0 to 10 is 0.5m wide, 10-20 is 1.0m wide. when hit 9.99 say it is still within the 0.5m geotechnical zone.

don't worry i am all good.

cheers mate.