Flight Line Separation
Use the Flight Line Separation option (geogxnet.dll(Geosoft.GX.AirborneQC.LineSeparation;Run)*) from the Airborne QC menu to carry out quality control on flight line separations.
Flight Line Separation dialog options
Application Notes
This GX assumes that the current database is the one containing the actual survey data. The database is called the survey database. If you wish to process a different database, you may browse to add it to the project or select one from the workspace list.
Current Database and Selection of Lines
It is advised that you carry out quality control on the survey lines (first letter of the line symbols being L) and tie lines (first letter of the line symbols being T) separately. By default, the option to process survey lines is checked. Select the Ties option in the Line type to process entry if you would like to check the separation between tie lines.
The Separation Calculation
Before the quality control test for compliance of line separations can be run, it is necessary to determine the spacing between lines for each point on the lines. This GX performs this function and saves the results to two channels: Closest_Left and Closest_Right. If the channels do not exist, the calculation is automatic, independent of the Recalculate separations option.
A nominal or average line spacing is required, as a grid is created internally to store flight path information. First, the lines are scanned to determine an average direction for the survey. This calculation takes into account the fact that lines may be flown in opposite directions. Separations are calculated perpendicular to this direction. The lines are scanned to determine their relative positions and paths through the survey area. Then, for each position, the perpendicular distance to the closest adjacent line is determined for both sides of the line. (Because the lines are not necessarily parallel, these distances are not necessarily the shortest distance to the other line.) The two channels created, Closest_Left and Closest_Right, contain the distance to the adjacent lines lying to the left and right of the current line, as seen proceeding in the average line direction. For instance, if the average line direction is 0° azimuth, then "Right" is at 90° and "Left" is at -90°. Where no line is found in these directions, the distance is left as a dummy value. This usually occurs near the ends of lines and on the "outside" of the lines at the edges of the survey. Once the initialization is completed, and the distance channels have been created, the compliance stage may be run any number of times, with different values, without re-calculating the distance channels.
- "Left” and “Right” are relative to the lines drawn on a map, with North at the top, based on the average direction for the lines and tie lines. Therefore, “left of line” and “west of line” are essentially equivalent.
- The line path grid created internally to facilitate the distance calculations uses a cell size of one-half of the nominal separation, and it can store information for up to two different lines at a time. This is adequate to handle crossing lines and surveys with a reasonable amount of deviation in the line paths. If there are sections of the survey where more than two lines cross a cell of this size, the algorithm may break down and miss the third (or other) line when locating adjacent lines. To remedy this, decrease the nominal line separation to ensure that no more than two lines will cross any square measuring half this distance on an edge.
Quality Control Specifications and Indicators
This GX allows two separate specifications to be applied to check whether the separations between actual flight lines are acceptable or not.
|
1) |
At each reading location, the distance to the nearest position on the nearest line should be less than the maximum separation. |
|
2) |
The distance of a flight line to the nearest line may be greater than the specified separation for a distance less than the specified distance. |
You can apply one or both of these specification tests. To disable a test, leave the field(s) empty.
The Compliance Test
Once the distance channels have been created, they may be used to test line separation compliance. The GX creates two flag channels, called Flag_SepL and Flag_SepR, which correspond to the two distance channels. These channels contain numbers from 0 to 3 inclusive to indicate the result of the quality control test on flight line separation.
A line may be in compliance with respect to a line on one side, but not in respect to the nearest line on the other side.
Indicator Definition
Each test is performed independently for the 'Left' and 'Right' sides.
|
Flag |
Description |
|---|---|
|
0 |
Flight line separation passes both tests. |
|
1 |
Flight line separation fails the maximum separation test. |
|
2 |
Flight line separation fails the test on the allowed line separation over a distance. |
|
3 |
Flight line separation fails both tests. |
Distance Calculation
When the specification of line separation over a distance is provided, the cumulative distance along the actual survey locations is used instead of the distance along the ideal line path.
*The GX.NET tools are embedded in the geogxnet.dll file located in the "...\Geosoft\Desktop Applications \bin" folder. If running this GX interactively, bypassing the menu, first change the folder to point to the "bin" directory, then supply the GX.NET tool in the specified format. See the topic Run GX for more details on running a GX.NET interactively.
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