This command allows you to calculate the station and offset of any entered or surveyed point relative to a known centerline or baseline. Note that the Station Store command will calculate a point at a given station and offset. Point Projection does just the reverse — it calculates a station and offset for any given point. It also will calculate the “Intersect”, or the projection of that offset point on the baseline. This baseline “intersect”, or perpendicular projection point, can be staked out and stored. The application of the routine is shown below.
The coordinates from which to project can be entered in three ways:
The station, offset, and vertical difference of the point is then calculated, and the Intersect button (see the above figure) will calculate the projected perpendicular intersect point on the baseline. This Intersect can also be staked out using the Stake button.
You must first define the baseline. You can define the baseline by one of the following methods:
If you choose two points, you must then define the line in the Point Projection dialog box as shown below.
With the two points method, you simply enter two point numbers, or choose them from the point list or MAP. The azimuth and slope between the two points is calculated, along with the ending station, based on the entered start station. With the Azimuth method, you define the line by entering a first point and then entering an azimuth and slope. You can confirm the coordinate values of the points by choosing Confirm NEZ. When the line is defined, choose Continue. You must now define, or designate, the point that is offset from the line in the Point Definition dialog.
You can enter a point ID, select one from the list, or select one from the map. You can also enter coordinates to define a new point, or read values from the instrument. As soon as enough information is entered, the station, offset and vertical difference is displayed or the message "OFF CENTERLINE" is displayed. This message lets you know that a station/offset cannot be computed for the coordinates entered.