To Create a Datum Point
1. Click > 
Datum Point. The DATUM POINT dialog box opens and the References collector in the DATUM POINT dialog box is activated.
Datum Point. The DATUM POINT dialog box opens and the References collector in the DATUM POINT dialog box is activated.2. Select a reference in the graphics window such as a plane, surface, edge, vertex, curve, or datum point. The selected references appear in the References in the DATUM POINT dialog box.
3. If you select a curve, edge, or a datum axis, select one of the following options in the Placement tabbed page to position the datum point.
◦ End of curve—Measures the distance from the selected end of a curve or edge. To use another endpoint, click Next End. For a curve or edge, End of curve is selected by default.
◦ Reference—Measures the distance from a selected entity. Select a reference entity, for example, a solid surface.
4. Specify one of the following options for offset distance:
◦ Ratio—Enter a value between 0 and 1 for the offset ratio in the Offset box. The datum point is placed on the selected curve or edge based on the Ratio specified. For example, if you enter the offset ratio as .25, the datum point is placed at 1/4 of the curve's total length.
◦ Real—Enter the actual length of the curve from the datum point to the endpoint of the selected curve or edge.
5. If you select a surface or a plane, you must specify two offset references. Click the Offset references collector and select two offset references in the graphics window.
6. You can also drag the reference handles in the graphics window to specify the references. When you drag the reference handles, IDD highlights valid references.
7. To add more points, click New Point in the DATUM POINT dialog box and perform steps 1 through 5 to create datum point.
8. Click OK in the DATUM POINT dialog box to create the datum point. The datum point appears in the graphics window and also appears as a separate node on the GTS Tree.
 | You can create multiple datum points within a single datum point feature. Each datum point thus created, appear as a separate node on the GTS Tree. |