Using the Transformation tab of the Drawing Settings dialog box, you can relate the local northing and local easting coordinates of your drawing to the grid northing and grid easting coordinates for the current zone.
The zone transformation settings do the following:
- Relate local coordinates to grid coordinates by transforming distances measured on the Earth (or geoid) to distances on an ellipsoid.
- Relate distances on the ellipsoid to the flat plane (projection) of the current zone’s grid coordinate system.
These transformations are accomplished through the use of scaling factors. First, a sea level scale factor is applied to the local values measured on the geoid, and then a grid scale factor is applied, which relates the ellipsoid values to the grid projection. The scaling factors can be defined in two ways:
- The sea level scale factor relates the distances on the geoid to the distances on the ellipsoid.
- The grid scale factor relates the distances on the ellipsoid to the distances on the grid projection.
You must also specify reference points in establishing transformation settings.
These reference points are the two points that tie the local and grid coordinates together. The reference points can be defined in two ways:
- By the grid and local coordinates of two known reference points in your drawing.
- By the grid and local coordinates of one known point and a known rotation to grid north.
To specify transformation settings for a drawing
- In Toolspace, on the Settings tab, right-click the drawing name
at the top of the collection, and click Edit Drawing Settings. - In the Drawing Settings dialog box, click the Transformation tab.
Important
You must specify the coordinate system on the Units and Zone tab before you can specify settings on the Transformation tab.
- Select the Apply Transform Settings check box to activate all the controls in the dialog box. Enter values as specified in steps 4-10. If you clear this check box, then controls in the dialog box are disabled and the AutoCAD X and Y coordinates match the coordinates in the specified zone.
- Select Apply Sea Level Scale Factor.
Tip
If you know the combined scale factor, then you can clear the Apply Sea Level Scale Factor check box, select User Defined as the Grid Scale Factor, and enter a combined scale factor in the Grid Scale Factor box. The combined scale factor is the combination of the scale factor for converting local to sea level and the scale factor for converting sea level to grid.
- Enter a default Elevation, such as the average elevation of your project site from sea level.
- Optionally, change the Spheroid Radius, which is the radius of a mathematical figure close to the shape of the Earth at sea level, approximately 6,370 km. The value shown in this box is initially derived from the current zone's ellipsoid and can be changed if local observations differ. In most cases, the default value shown is the accepted value.
- For the Grid Scale Factor, select a method for Computation. For more information, see Transformation tab.
- Specify the Reference Point values. The reference point could be a benchmark that was used in a survey. It can be any point for which you know both the local coordinates and the grid coordinates. To specify the Reference Point values, do one of the following:
- Click the Select Point button and then select a point in the drawing, or use Transparent commands.
- Enter a point number.
- Enter the point's Grid Northing and Grid Easting values.
- To define the rotation angle for the transformation, do one of the following:
- Click the Select Point button and then select a point in the drawing.
- Enter a point number.
- Enter the point's Grid Northing and Grid Easting values.
- Specify the grid rotation angle.
- Click OK.
