Carrying Elevations in a Traverse

Starting a Traverse With an Assumed Elevation

Choose View | Format View (or press [F9]) and add the letter Z to the Display Sequence.
Back in the Traverse View move the cursor to the Z field and enter the assumed elevation of the first occupied point.

All of the subsequent elevations will be computed based on this elevation. If you start a traverse with a new point, its elevation is zero.

Later, when you find out what the actual elevation is, just enter the correct elevation and choose Tools | Recompute. TPC will update all the elevations based on the new elevation you entered.

Entering Instrument Heights

One way to carry elevations in a traverse is to establish elevations for your control points, then measure the height of the instrument above the control point at each occupied point.

Choose View | Format View (or press [F9]) and add the letter 'I' to the display and editing sequences.
Now enter the instrument height data for each occupied point.

The default instrument height for each new occupied point is zero.

Note: The elevation of the instrument is not displayed in the Traverse View. Only the elevation of the control point and the HI are displayed.

Entering Target Heights

Choose View | Format View (or press [F9]) and add the letter 'T' to the display and editing sequences.

TPC subtracts the target height from the elevation of the target to get the elevation of the foresight point.

As you add points to a traverse, TPC copies the target height of the last traverse point into the appended point. As long as you don’t change the target height, you don’t have to edit it. If you do change the target height for a shot, just move the cursor to the HT field and enter the new value.

Negative Instrument Heights and Target Heights

In tunnels or underground mining operations, it is not uncommon to put control points and benchmarks in the ceiling. In these instances, you will need to use negative instrument and target heights. TPC allows negative numbers for both instrument heights and target heights.

Using Benchmarks

Benchmarks are points of known elevation. When you take a shot on a benchmark, the elevation of the benchmark along with the target height, slope distance and vertical angle is used to establish the elevation of the instrument’s optics.

In TPC, each occupied point can have one tie to a benchmark. A benchmark does not require a horizontal angle or bearing tie.

Note: The only restriction is that the benchmark point must immediately follow the occupied point or backsight point and cannot follow a sideshot.

If you do not know the elevation of a benchmark, you can always assume an elevation, then enter the correct elevation at a later time and choose Tools | Recompute.

If the benchmark point already exists, recall it into the Traverse View. If not, create a new point and enter the benchmark elevation.
Choose Type | Benchmark.
Enter the slope distance, vertical angle and target height of the shot to the benchmark. The elevation of the instrument optics is computed and stored internally.

The HI for the benchmark point displays the elevation difference between the optics elevation and the elevation of the control point. If the control point elevation and the benchmark elevation are on the same grid, the HI should be close to the measured HI.

Including Check Elevations in your Traverse

It is always a good idea to tie at least one point of known elevation other than the control point or benchmark used to establish the elevation at each occupied point.

Include a side shot to the point of known elevation. Put a note like “=BM14” in the point description for the side shot so that you know which side shot was the check.
Once the side shot has been computed, choose COGO | Random Inverse and enter the point labels for the side shot and the point of known elevation. The random inverse dialog box will display the difference in elevation between the two.

Note: In this situation, where the benchmark may or may not also have a coordinate position, the HD, SD, VA and % displayed in the random inverse dialog box are of no consequence. The only important number is the VD (vertical distance).

Translating to a Known Elevation

Another way to establish the elevation of a traverse is to take a side shot to a point of known elevation. When the traverse is finished, translate the traverse so that the elevation of the side shot is the same as the known elevation using the Translation dialog.

The disadvantage to this method is that all the points (even the control points) in the traverse will be translated up or down. You can get around this problem by recalling the points you want to translate into a separate traverse and translating that traverse.

Entering Elevations of Foresights and Side Shots

There are times when you will want to enter elevations for foresights and side shots which are computed from raw data (SD, VA, HA). This situation occurs, for example, when you run differential levels through control points. The Traverse View has computed elevations based on the raw data, but you want to enter your own elevation and have the program ignore the computed elevation.

TPC treats every number you enter as raw data. Just enter the new elevation in the Traverse View. If the point is recomputed, the elevation you entered will take precedence over the elevation computed from a prior raw data entry.

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