Intersections

Use the Tie Line Levelling > Intersections menu option (geogxnet.dll(Geosoft.GX.Levelling.Intersections;Run))* from the Geophsyics Levelling extension to create an intersections table. Difference statistics on intersections deviations can be calculated and saved to an output file.

Intersections dialog options

Data channel	Select the data channel. Script Parameter: INTERSCT.InZ
Intersection tolerance	This parameter is only relevant when the initial intersections table is created. The intersection tolerance is the maximum distance between non-intercepting survey lines and tie lines within which the closest two points of the two lines are extracted and added to the intersections table (see Figure 1). If left blank, the tolerance is set to ten times the nominal sample spacing. You can only specify a tolerance smaller than this limit. Script Parameter: INTERSCT.Tol
Tie lines or all lines	Select "All lines" or "Tie lines". This parameter is ignored if an existing intersections table or database is used as input. Script Parameter: INTERSCT.Lines
Existing intersections table	Select an existing intersections table or database to get intersections from. This is an optional field; if specified, instead of recalculating the intersections from the database, they are read from this table or database file. For large databases the time saved can be substantial. Script Parameter: INTERSCT.OldTable
Output intersections table	Specify the name of the output intersections table/database. You can also click the browse [...] button to select (and overwrite) an existing file. Script Parameter: INTERSCT.Table
Output statistics file	Specify the output statistics file name. You can also click the browse [...] button to select (and overwrite) an existing file. This is an optional field; if specified, the statistics (minimum, maximum and standard deviation values) on the survey/tie line intersection deviations are reported in this file. See the Application Notes below for more details. Script Parameter: INTERSCT.StatsFile

Application Notes

The first step in leveling tie lines and regular survey lines is to produce a tie line intersections table or database.

Figure 1: The intersections table is being generated.
A) The closest readings on each of the survey and tie lines are 7.5 nominal sample spacings apart (grey dashed line). If the Intersection tolerance field is left blank or entered to be between 7.5 and 10 sample spacings, the point marked with the blue cross will be added to the intersections table along with the details of the points marked with red +s. On the other hand, if the provided intersection tolerance is less than 7.5 sample spacings, the point marked with the blue cross will not be added to the intersection table.
B) The closest points on each of the survey and tie lines are six nominal sample spacings apart (grey dashed line). Only the Intersection tolerance values greater than six sample spacings will trigger an entry in the tolerance table.
C) The closest points on each line are twelve sample spacings apart. Regardless of the Intersection tolerance value, no intersection point will be added in the intersection table.

Intersections Table Format (*.tbl)

The output intersections table file tabulates every intersection between tie lines and regular survey lines. It includes the exact ground location of the intersection point, the tie line and survey line numbers, the recorded value on each line, and the horizontal gradient of the data at that location.

Example of an intersection table:

/ Intersection Table / / X Y Tie# TFid TZ TDZ Line# LFid LZ LDZ 8094.09 5336.51 90 1306.97 64180.2 0.068 470 574.133 64197.8 0.463 8106.99 1893.43 90 1409.55 64207.2 0.445 471 2276.95 64266.1 0.211 8049.27 7721.71 90 1030.20 64069.9 0.556 510 599.391 64065.8 0.155 8082.4 6688.47 90 1170.74 64116.5 0.421 490 2304.9 64130.0 0.526 7983.82 0078.85 90 777.000 64078.9 0.558 550 649.575 64069.6 1.376 8058.46 7854.91 90 876.391 64050.9 0.132 530 2282.74 64075.1 0.009 7997.32 2392.99 90 472.451 63904.9 0.759 590 881.501 63852.4 1.427

If the intersection tolerance is greater than 0.0, the points of closest approach within the tolerance will also be recorded, where lines do not actually intersect. The location will be the average of the closest points on each line.

The columns of the table:

X	X coordinate of the intersection
Y	Y coordinate of the intersection
Tie#	Tie line number
TFid	Tie line fiducial
TZ	Tie line reading
TDZ	Tie line gradient (per fiducial)
Line#	Line number
Lfid	Line fiducial
LZ	Line reading
LDZ	Line gradient (per fiducial)

Intersections Database (*.gdb)

The Geosoft database can be used to store the intersections information. This has several benefits:

1. The exact intersections locations can be plotted to a map using the normal mapping and symbol methods.

2. Quantities such as the mis-tie or gradient values can be easily gridded for display.

3. Intersections are sorted by Tie Line, instead of appearing as a single long list.

To create an intersections database, simply run the Levelling Intersections GX and specify a file of type (*.GDB) as the output intersection table. The XLEVEL GX recognizes both the original *.tbl file format and the new Geosoft Database file as inputs. Each Tie in the intersection table gets its own line in the Geosoft Database file, containing all the line intersections with that tie line.

The channels of the intersections database:

X	X coordinate of the intersection
Y	Y coordinate of the intersection
TIE	Tie line number
TIE_FID	Tie line fiducial.
TIE_LEVEL	Tie line reading.
TIE_GRAD	Tie line gradient (per fiducial).
LINE	Line number.
LINE_FID	Line fiducial.
LINE_LEVEL	Line reading.
LINE_GRAD	Line gradient (per fiducial)
Intersection_dX	Difference (at each intersection) between the closest X along the survey line and the closest X along the tie line.
Intersection_dY	Difference (at each intersection) between the closest Y along the survey line and the closest Y along the tie line.
Intersection_dDist	Distance (at each intersection) of the intersection deviations, calculated as:
Intersection_dData	Difference (at each intersection) between the closest data reading along the survey line and the closest data reading along the tie line.
CROSS_DIFF	Miss-tie value (LINE_LEVEL - TIE_LEVEL). Note that when the XLEVEL GX is used to extract mis-tie values to the flight database using the "Level Lines" option, the resulting CROSS_DIFF values in the flight database are of the opposite sign, i.e. TIE_LEVEL - LINE_LEVEL.

Intersections Statistics File

The following difference statistics (minimum, maximum and standard deviation values) on the survey/tie line intersection deviations are calculated and reported in the output file:

	Min	Max	StdDev
X_Position	Intersection_dX_min	Intersection_dX_max	Intersection_dX_Dev
Y_Position	Intersection_dY_min	Intersection_dY_max	Intersection_dY_Dev
Distance	Intersection_dDist_min	Intersection_dDist_max	Intersection_dDist_Dev
Data	Intersection_dData_min	Intersection_dData_max	Intersection_dData_Dev