Intersection Levelling (Moving Platform)

Use the Moving Platform Gravity > Intersection Levelling menu option, (geogxnet.dll(Geosoft.GX.UAVSurvey.IntersectionLevelling;RunWithZeroTrend)*), to perform tie line levelling on the gravity data.

Intersection Levelling dialog options

Input data channel

Select the data channel to perform tie line leveling on.

Script Parameter: PLAN_UAV_SURVEY.INPUT_CHANNEL

Intersection tolerance

Specify the intersection tolerance in distance units. If set to 0.0, points on the survey and tie line must coincide to be identified as an intersection. If set to > 0.0, the points of closest approach to the intersection that are within the tolerance will be used. An intersection table is created that is subsequently used.

Script Parameter: PLAN_UAV_SURVEY.INTERSECTION_TOLERANCE

Maximum gradient per fiducial

Specify the maximum gradient in data units per fiducial. If this value is defined, then only intersections with both line and tie-line gradients less that this limit will be added to the intersection table. Initially, it is recommended to include all intersections by providing a large maximum gradient value and observe how well the data is levelled. You can then opt to refine this parameter and establish a reasonable limit according to the outcome.

Script Parameter: PLAN_UAV_SURVEY.MAX_GRADIENT_PER_FID

Recalculate intersections

An intersection table is created using the above three parameters and saved in the working folder. The name of this table is "_TempOutputIntersection.tbl". This table is used if Intersection Levelling is invoked again, and the above parameters are ignored. To recalculate the intersection table with new parameters, check this option and run Intersection Levelling again.

Script Parameter: PLAN_UAV_SURVEY.RECALCULATE_INTERSECTIONS ( 0 – No, 1 –Yes)

Output levelled channel

Specify the output levelled channel.

Script Parameter: PLAN_UAV_SURVEY.OUTPUT_LEVELLED_CHANNEL
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All subsequent parameters have default settings. To customize them, expand this section.

Cross-level channel

The optional output channel in which to place the final cross level values, after the levelling is completed. These are the values of the crossing lines at the intersections with the line being viewed. The level channel is not required, but it can be useful to view the tie line levels graphically in profile when determining the acceptance of each intersection.

Script Parameter: PLAN_UAV_SURVEY.CROSS_LEVEL_CHANNEL

Difference channel

Upon completion of the levelling, the difference between the survey lines and tie lines is written to this channel. It is also used during the levelling process to store the current mis-tie values.

Script Parameter: PLAN_UAV_SURVEY.DIFFERENCE_CHANNEL

Cross-gradient channel

The optional output channel in which to place the gradient of the tie line at the intersection point. These are the final gradient values, after the levelling has been completed. This channel is also not required, but the information can be used to decide if a suspicious tie point is located in a high gradient along the crossing line.

Script Parameter: PLAN_UAV_SURVEY.CROSS_GRADIENT_CHANNEL

Application Notes

Tie-line levelling is a technique used to adjust the data along each survey line in order to minimize the discrepancy between lines and tie lines where they intersect.

Intersection levelling involves the following steps:

  1. Produce a table of the intersection crossing coordinates and the discrepancy between the survey and tie line data at these crossings.
  2. Calculate the average difference between tie and survey lines at all identified crossings.
  3. DC shift the tie lines by this average.
  4. Adjust the survey line data to match the tie line data at the crossings.

After running this GX, grid the levelled data to check if it is adequately leveled. If any levelling artifacts are still present in the data, run the intersection leveling process on the leveled channel.

*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.