shapeObj.getCentroid question - Mapscript_csharp

[David Lowther]

Sorry for the mass postings.

 

I've noticed that getCentroid behaves differently after projection of the
shapeObj based on whether you reproject the shape or a clone of the shape.
Not clear? No lie, I had a hard time typing the sentence.

 

In the following example you can see that I can get the right answer, I was
just wondering if someone could explain the difference in behavior.

 

Here's an example:

 

Partial Class ProjectPointGetCentroid

    Inherits System.Web.UI.Page

 

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As
System.EventArgs) Handles Me.Load

        '//project a shapeObj and getCentroid returns coordinates in
previous projection

        TestProjectNOClone()

        TestProjectClone()

    End Sub

 

    Private Sub TestProjectNOClone()

        '//Incorrect Result

        '//pCent will equal oCent

 

        Dim albProj As String = "+proj=aea +lat_1=29.500000000
+lat_2=45.500000000 +lat_0=23.000000000 " _

            & "+lon_0=-96.000000000 +x_0=0.000 +y_0=0.000 +datum=NAD83
+ellps=GRS80 +no_defs"

        Dim llProj As String = "+proj=longlat +ellps=GRS80 + no_defs"

 

        Dim shp As New shapeObj(MS_SHAPE_TYPE.MS_SHAPE_POLYGON)

        Dim shp2 As New shapeObj(MS_SHAPE_TYPE.MS_SHAPE_POLYGON)

        Dim line As New lineObj()

        Dim pt As New pointObj(-100, 35, Nothing, Nothing)

        line.add(pt)

        pt = New pointObj(-100, 36, Nothing, Nothing)

        line.add(pt)

        pt = New pointObj(-101, 36, Nothing, Nothing)

        line.add(pt)

        pt = New pointObj(-101, 35, Nothing, Nothing)

        line.add(pt)

        pt = New pointObj(-100, 35, Nothing, Nothing)

        line.add(pt)

        shp.add(line)

 

        Dim oCent As pointObj = shp.getCentroid()

        Dim result As Integer

        result = shp.project(New projectionObj(llProj), New
projectionObj(albProj))

        Dim pCent As pointObj = shp.getCentroid()

 

    End Sub

 

    Private Sub TestProjectClone()

        '//Correct Result

        '//pCent will NOT equal oCent

 

        Dim albProj As String = "+proj=aea +lat_1=29.500000000
+lat_2=45.500000000 +lat_0=23.000000000 " _

            & "+lon_0=-96.000000000 +x_0=0.000 +y_0=0.000 +datum=NAD83
+ellps=GRS80 +no_defs"

        Dim llProj As String = "+proj=longlat +ellps=GRS80 + no_defs"

 

        Dim shp As New shapeObj(MS_SHAPE_TYPE.MS_SHAPE_POLYGON)

        Dim shp2 As New shapeObj(MS_SHAPE_TYPE.MS_SHAPE_POLYGON)

        Dim line As New lineObj()

        Dim pt As New pointObj(-100, 35, Nothing, Nothing)

        line.add(pt)

        pt = New pointObj(-100, 36, Nothing, Nothing)

        line.add(pt)

        pt = New pointObj(-101, 36, Nothing, Nothing)

        line.add(pt)

        pt = New pointObj(-101, 35, Nothing, Nothing)

        line.add(pt)

        pt = New pointObj(-100, 35, Nothing, Nothing)

        line.add(pt)

        shp.add(line)

 

        Dim oCent As pointObj = shp.getCentroid()

        Dim pShp As shapeObj

        pShp = shp.clone()

        Dim result As Integer

        result = pShp.project(New projectionObj(llProj), New
projectionObj(albProj))

        Dim pCent As pointObj = pShp.getCentroid()

 

    End Sub

End Class

 

Thanks,

 

David Lowther 

 

Coordinate Solutions, Inc.

501 N.E. 15th Street

Oklahoma City, OK 73104

405.246.9396 (Voice)

904.471.5548 (Fax)

www.coordinatesolutions.com

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