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

    If the X & Y channels are not assigned in the active database, run Set Coordinate System to set the current X & Y channels and then run this tool again.

    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

      The XLEVEL GX can be used to extract levelling corrections from the intersection table.

      The STATLEV GX and the FULLLEV GX can then be used to apply the levelling corrections to the data.

    *The GX tool will search in the "...\Geosoft\Desktop Applications \gx" folder. The GX.Net tools, however, are embedded in the geogxnet.dll 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" folder, then supply the GX.Net tool in the specified format.