By Xiaodong Liang

A customer wanted to get the closest point on a drawing curve when the user clicks a location on the sheet. The workflow is simple: start mouse event, watch MouseEvent.OnMouseClick. In the event, calculate the closest point on the curve.

However, it looks API only provides GetClosestPoint method for Edge and Face. So we would need to calculate the closest point ourselves. There are many discussions on the algorism how to get a nearest point of 2D curve, I tested with the simplest one: disperse the parameters of a curve, then get the point, calculate the distance with the mouse point, find the shortest one.

The below is the code of MouseEvent. The whole code project is attached. It is a standalone EXE. It assumes a drawing curve is selected, then click [start event], mouse click a location, the closest point will be displayed as a client graphics point. Click [stop event] to terminate the custom mouse event.

Download ClosesPoint

you can change to other more efficient algorism of getting close point.

Private Sub oME_OnMouseClick(Button As MouseButtonEnum, ShiftKeys As ShiftStateEnum, ModelPosition As Point, ViewPosition As Point2d, View As View) Handles oME.OnMouseClick
Dim oPickPtX = ModelPosition.X
Dim oPickPtY = ModelPosition.Y
Dim oCurve As DrawingCurve
oCurve = oOneDrawingCurve.Parent
Dim oEvaluator As Curve2dEvaluator
oEvaluator = oCurve.Evaluator2D
Dim oMinP, oMaxP
oEvaluator.GetParamExtents(oMinP, oMaxP)
Dim oMinDis = 100000000000.0
' Get the curve length
Dim dLen As Double
Call oEvaluator.GetLengthAtParam(oMinP, oMaxP, dLen)
Dim dInc As Double
dInc = dLen / 100 'consider 100 points
Dim dLenInc As Double
dLenInc = 0
Dim dparams(0) As Double
dparams(0) = oMinP
Dim iCnt As Integer
Dim oClosestPtX As Double = 0
Dim oClosestPtY As Double = 0
For iCnt = 0 To 100
Dim dParam As Double
Call oEvaluator.GetParamAtLength(oMinP,
dInc * iCnt,
dParam)
' a spline in planar sketch is 2d. its points are
' 2d (x,y)
Dim dPts(1) As Double
dparams(0) = dParam
Call oEvaluator.GetPointAtParam(dparams, dPts)
Dim oEachDis = Math.Sqrt(Math.Pow((dPts(0) - oPickPtX), 2) +

Math.Pow((dPts(1) - oPickPtY), 2))
'smaller distance?
If (oEachDis < oMinDis) Then
oMinDis = oEachDis
oClosestPtX = dPts(0)
oClosestPtY = dPts(1)
End If
Next
'draw the point graphics
Dim oCoordSet As Object = Nothing
Dim oGraphicsNode As Object = Nothing
Dim oDataSets As Object = Nothing
'get datasets, dataset, graphics node
getCG(oGraphicsNode, oCoordSet, oDataSets)
'prepare the coordinates
Dim oPointCoords(2) As Double
oPointCoords(0) = oClosestPtX : oPointCoords(1) = oClosestPtY : oPointCoords(2) = 0
'oPointCoords(0) = dPts(0) : oPointCoords(1) = dPts(1) : oPointCoords(2) = 0
Call oCoordSet.PutCoordinates(oPointCoords)
'add PointGraphics
Dim oPointGraphics As PointGraphics
oPointGraphics = oGraphicsNode.AddPointGraphics
'set the related
oPointGraphics.PointRenderStyle = PointRenderStyleEnum.kCrossPointStyle
oPointGraphics.CoordinateSet = oCoordSet
oPointGraphics.BurnThrough = True
invApp.ActiveView.Update()
End Sub