Single Proportion Dialog

This dialog computes the position of a lost corner using Single Proportionate Measurement.

You can initialize most of the dialog data by selecting the lost corner (assuming you've already created a record position) in a traverse before opening this dialog.

BLM Method

The method used is that described in the 2009 BLM Manual of Survey Instructions. The reports will include the text "BLM Manul" in the report headings to remind you of the method used on any printouts.

Steps

1. Recall the existing (controling) corners.
2. Recall the Lost Corner (TPC inverses the existing corners) or enter the record data.
3. Recall the Temporary Corner (TPC inverses the existing corners) or enter the retrace data.
4. Tell TPC whether or not you want to compute the latitudinal offset for East-West lines.
5. Choose Summary to check the computations.
6. Enter a Computed Point (you can reuse the Lost Corner label to update it's position) and choose Save.

Existing Corner - North, South, East, West

Starting at the top of the dialog, enter the existing corner your record calls start at. Move down the dialog in the direction of your calls to the other existing corner near the bottom of the dialog. This works for any direction - Westerly, Easterly, Northerly or Southerly.

Initializing Corners

If you select a control point in a traverse then open this dialog, TPC initializes the dialog as follows:

• The selected point becomes both the Lost Corner and the Temporary Corner. TPC doesn't know which one you want the selected point to be, so it initializes both fields. Now you can recall a different point or just enter data.
• The preceeding control point (above the selected traverse point) becomes the top Existing Corner.
• The proceeding control point (below the selected traverse point) becomes the bottom Existing Corner.
• TPC computes the inverses between the Existing, Lost and Temporary corners and uses these as the initial record and retrace data.

As a result of this default initialization, some of the data in the dialog will be correct and some will need to be updated. Just type over any data to enter the correct data.

If you have closed this dialog and wish to re-open it with all the data intact (without re-initializing), use the COGO command from the TPC desktop to open this dialog.

When you recall an existing Lost or Temporary corner, TPC computes the inverses for any bearing or distance you have not already entered. So if you have already computed a record position for the lost corner or a temporary position based on a retracement, you can quickly populate the dialog data by recalling those points.

Note: These points that you recalled for Lost and Temporary corners are not recomputed by this dialog. Their coordinates and point labels are copied into the dialog for the purpose of insersing the record and retracement data.

If you have not physically measured between the existing corners, you may want to assume the temporary corner is at the midpoint between the existing corners. TPC lets you do this easily in this dialog using equations. Lets look at the following example:  EastCorner----------(midpoint)----------WestCorner

• For the East corner bearing, enter EastCorner..WestCorner and press [Enter].
• For the East corner distance, enter EastCorner..WestCorner/2 and press [Enter].
• For the West corner bearing, enter WestCorner..EastCorner and press [Enter].
• For the West corner distance, enter WestCorner..EastCorner and press [Enter].

Dividing the inversed distance bewteen the two corners by 2 created retrace data to the assumed midpoint.

The computed position of the Lost Corner is updated with each change you make to the data in the dialog. Any time you choose Summary or Save the computed point, you are using the current computed position. The Summary button is a great way to see how TPC has computed the lost corner.

The computed position of the lost corner is not actually used until you Save the computed point.

You can update any existing survey point with the computed lost corner coordinates by recalling its point label in the 'Computed Position of Lost Corner' field. TPC will ask if you want to update the existing point with the computed coordinates. Say Yes.

You can also save the computed position to any new survey point by entering an unused point label.

Professional