Transform Points

Icon:
Menu:	Surfaces > Transform Points
Ribbon:	Surfaces Tab > COGO Points and Survey Panel > Edit Point dropdown > Transform Points Site Tab > CSD/Civil 3D COGO Point Tools > Edit Point dropdown > Transform Points Stringer Survey Tab > Civil 3D COGO Point Tools panel > Transform Points Survey Tab > COGO Points Panel > Transform Points

 

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Introduction

This command will apply a 2D Helmert or 2D Affine transformation, using control point coordinates applied to COGO Points.  The transformation is performed on a group of points by calculating using select reference point coordinates (matching to points in the group).

Users can import a points file with control point coordinates or type the coordinates in for the known/fixed coordinates.  When importing a point file of coordinates, the point numbers in the file are used to match with points with the same point numbers in the drawing.

The transformation can be limited to a selected point group.

When applying transformational change, tick on the 'Use' coloumn in the form for the selected Civil Point to use it in the transformation calculations.

A 2D Affine transformation requires 3 points for transformation.  For an affine transformtion to occur, points cannot be colinear.

A 2D Helmert transformation requires at least 2 points for a 2D transfomration.  Include more points for a more accurate transformation - when more than 2 reference points are included, the calculation is made by applying a Gaussian least squares method.

Notes:

• The 'Use' Column can be selected to sort the points based on whether they are being used in the transformation or not

• It is recommended to set the Point Group to 'All Points', so that the transformation applies to every point in the drawing (unless some are specifically to be excluded from the transformation)

Details

Upon selecting the command the following form is displayed:

Point Group	Select the point group to include points for transformation.
Select Target Point	Select a point in the drawing to adopt the coordinates from that point.
Import Control Points	After selecting this command a form will display to navigate to and select the file containing coordinated points to use for transformation. After selecting a file the Select File Format form will display:   Point File format Use the picklist to select a Point File Format that matches with the format of the point file selected. OK Add the control points to the transformation
List of Points	This lists all the points contained in the selected Point Group.
Use	Tick on to use these points in the transform calculations.  Using Import Control Points will automatically set these points to Use.
Point Number	Point number (non editable)
Easting	Easting (non editable)
Northing	Northing (non editable)
Target Easting	Type in (or import) the easting coordinate to use
Target Northing	Type in (or import) the northing coordinate to use
Residual Easting	Displays the adjusted coordinates for the point
Residual Northing	Displays the adjusted coordinates for the point
Calculate	Calculate the adjustment and check the Residual Easting and Residual Northing.  Also updates the information panel to the right with the results summary (RSS - Residual Sum of Squares). Calculate allows a review of the results before committing to the drawing.
Method	Select the method for applying the transformation
Helmert	Apply a Helmert transformation
Affine	Apply an Affine transformation
Datum Shift	A change in the elevation of all points in the selected Point Group can be applied here
Shift Value	Type in a +- value
Apply Datum Shift	Click to apply the change in elevation to all points listed
Apply Transformation	Click to apply the transformation to points in the drawing.  A confirmation form will display.  After confirming the change, point coordinates will be adjusted for the selected points in the point group
Close	Apply and exit.