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Introduction
Navigation can be imported several ways in Geocap. The two main ones are:
- SEG-Y 2D navigation
- UKOOA navigation
Both of these can be imported into a Generic folder.
Details
Importing SEG-Y 2D navigation
Importing SEG-Y 2D navigation means that the user imports the UTM X and -Y coordinates for each trace in the SEG-Y file, in addition to the shot points of each trace.
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Remember that not all SEG-Y files contain navigation. |
Example of importing SEG-Y 2D navigation
Scan file (1)
Unless you are very familiar with the SEG-Y file you are importing we always suggest you scan the file, by clicking the Scan button, to make sure that the settings are correct. The results of the scan can be observed by clicking on the Scan Results tab. The shot point-, X-, and Y ranges are reported. The Z (time) range is also reported but ignored in the final import (all Z's are set to 0 in the resulting dataset).
Check shot point byte position (2)
The default settings are usually correct. However, one of the more common adjustments is the shot point's byte position. This defaults to byte position 17-20 in the trace header. To find the correct byte position select the Trace header tab. Here you can view the SEG-Y file's headers trace by trace. The byte positions' values are continuously reported as you move through the file. There are buttons for going backwards, forwards, start and end of the file. By closely observing how the values change you should be able to determine the correct byte position. Use the Shot point, Byte pos. spinbox to set the appropriate byte position.
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Shot points often appear in pairs, i.e. they change every other trace. |
Check scaler value (3)
Another common adjustment is for the Scaler - set by default to byte position 71-72. The scaler determines the multiplication factor for X and Y, so if these values are to high or to low, you can adjust the multiplication using the From file drop down box.
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The SEG-Y format states that a negative Scaler denotes division, e.g. Scaler = -10 means divide X and Y with 10. The drop down for fixing the multiplication factor, on the other hand, uses pure multiplication, e.g. Scaler = 0.1 means multiply X and Y with 0.1. |
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The scaler may be 0 on file. This will lead to X and Y being 0 in the dataset. Fixing the Scaler to 1 is usually the correct setting in this case. |
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You can always click the Defaults button to get back to the default settings. |
Importing UKOOA navigation
Navigation is often stored in UKOOA/P190 format as ascii files.
Select either UKOOA Lat Lon or UKOOA xy, depending on you files coordinate format. The only difference between these two is that UKOOA xy will have less columns for the coordinate input.
The ASCII import will load with default values, ready to read the UKOOA format. After browsing in the UKOOA file observe that the file columns are interpreted correctly.
Example of UKOOA Lat Lon import
If necessary, make the required adjustments to the column position settings, using the controls marked in the image above.