Geometric Control of Lines with Point Measurements

Introduction

Geometric control against a line is essentially a line control. This means that we check a measured point against a line in the application layer. The program calculates the theoretical point on the line differently depending on which method we choose. When the theoretical point has been calculated, the program finds the deviation between this and the measured point.

We can also use the function Geometric control road... With this, you can check the center line in an SFI model, as well as lines defined by surfaces in the model.

In the dialog for geometric control of a line, we have five different methods:

1. 2D
2. Height
3. 2D/Height
4. 3D
5. 2D-corner

2D

With this method, the program does not take height into account when calculating the theoretical point.

DIFF_ERROR (the difference) is found by going normally to the line in the map plane. In addition, the program also calculates D_EAST and D_NORTH.

The sign of DIFF_ERROR tells whether the point is on the left or right side of the line (negative value means left side seen in the line direction).

Height

With this option, only D_HEIGHT is calculated. DIFF_ERROR and D_HEIGHT will in this case be equal.

Height-only method for vertical deviations.

2D/Height

Often, we want to report separate tolerances on 2D and height simultaneously. In many cases, the normal distance to the line + height deviation is what's interesting to report, not the 3D deviation as a combined deviation.

3D

With this method, the theoretical point is calculated by going normally to the line in 3D.

In addition to DIFF_ERROR (the difference), D_EAST, D_NORTH, and D_HEIGHT are also calculated.

3D method showing normal projection to the line in three dimensions.

2D-corner

The 2D-corner method is basically similar to the 2D method. In addition, DeltaA and DeltaB are calculated in relation to the nearest corner or, in other words, the nearest break point on the line. A line object can contain many corners, all of which can have a DeltaA and DeltaB value calculated. As we can see from the figure, the DeltaA and DeltaB deviations are normal to element A and element B respectively, or possibly on the extension of these elements.

Figure: P = Measured point

It doesn't matter whether the measured point is inside or outside the line object. A is the element before the break point and B is the element after the break point against which it is calculated. We see that the direction of the line is therefore decisive for what becomes DeltaA and DeltaB.

We specify the tolerance requirement in the control, from Min. tolerance to Max. tolerance.

Control Results

Horizontal List Field

After the control is performed, the program outputs the result of the calculation in the layer with measured control points.

Result of calculation in horizontal list field

The following properties can be available in the horizontal list field:

• DIFF_ERROR - the vector deviation (difference)
• D_EAST - the East component of the vector deviation
• D_NORTH - the North component of the vector deviation
• D_HEIGHT - the Height component of the vector deviation
• DELTA_A - deviation normal to line A (calculated only for the 2D-corner method)
• DELTA_B - deviation normal to line B (calculated only for the 2D-corner method)
• CONTROL_RESULT - the control result of the point. If the deviation is greater than the tolerance requirement, we get an X in the column.

Report

In addition to the result being shown in the horizontal list field, we also get a dedicated Excel report for the control.

Example of Excel report for geometric control