Program: LOCPREP

Title: Location File Editor

Version: 2.9

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1. Introduction

LOCPREP is an interactive editor for Lynx and UKOOA type location files, which store seismic shotpoint location information, and can also store general location information. You can use LOCPREP to perform a variety of tasks with LOC files, including renaming lines, editing or deleting or renumbering shotpoints and joining and splitting lines.


2. Running LOCPREP

If no LOC file is specified on the command-line, open a LOC file using the File-Open menu, or by dragging a LOC file onto the LOCPREP window from an Explorer window.
You can change the display and annotation options for the location file using the Options-Edit Parameters menu.
The Tasks menu lists the editing options available within LOCPREP for manipulating the LOC file. Some options require a seismic line, or multiple seismic lines, to be selected before the option is available. To select lines from a list, use the Select-Select Object From List menu option which displays a list of the seismic lines in the current LOC file - this list can be sorted by clicking on the header row of the list. To select lines on the map, use the Select-Select Object menu option - select a single line by clicking near it, and select multiple lines by holding down the <CTRL> key while selecting the second and subsequent lines.
When you have completed editing, use the File-Save As menu to save your LOC file.


2.1 Command-line options

LOCPREP can be started with a command-line similar to the following:

LOCPREP [-cPROJFILE] [LOCFILE]

where:

PROJFILE is the full path of an optional projection configuration file with a LPJ extension, used for map projection conversions. This file can be created using the Projection-Save Projection File menu.

LOCFILE is the full path of a LOC file to open on program startup.


3. Menus and Controls

3.1 Main Menu


4. Create New Profile from Intersections

If a profile is missing from the location file and from the map, you may be able to reconstruct its SP locations by looking for its intersections on the top strips of other profiles in the same area. You need the paper displays for these profiles, with the intersection information along the top strip (or raster images, or intersection listings). These lines must also be in the current .LOC file.

Make a list of the intersections, in the form

SP Linename SP-on-missing-Line

Select the Create New Profile  option and enter a name for the new profile. Now use the mouse to digitise the known points of your new profile where it crosses other profiles. Each time you select a point, a dialogue box will prompt you for the new shotpoint number, and you can confirm or edit the shotpoint of the profile it crosses.

When you have completed digitising, select the Create New Profile  option again to un-toggle it and save your new line into the current temporary LOC file.

You can now edit the new profile, sort its shotpoints and interpolate the location points to a regular SP interval to create a regular profile which matches the other lines in the same survey.


5. Edit Records for Current Profile

The Edit Records  option enables the fields in individual records to be altered manually.

Records for the current profile are displayed in a new window:

The buttons and popup menu provide the following functions:

Click OK to save your changes to the current temporary LOC file, or Cancel to discard your changes


6. Edit File Header

The Edit File Header   option allows the UKOOA header records in the LOC file to be viewed and edited.

The buttons and popup menu provide the following functions:

Header records must be prefixed by a 'H' character.
The UKOOA 84 and 91 standards list mandatory and optional header records with the header codes to use. Lynx LOC files have no mandatory headers, but none of the existing headers will be deleted, as long as all header records precede all data records.

Click OK to save your changes to the current temporary LOC file, or Cancel to discard your changes


7. Join Profiles

The Join Profiles   option enables two profiles whose endpoints are close or overlapping to be joined as one profile. The shotpoint sequence on the new profile becomes continuous and is inherited from the profile selected as the primary profile.

First, examine the profiles to be joined and decide the shotpoint on the primary profile at which the join is to take place. The location points in both profiles should be ordered so that the profiles both go in the same direction and the secondary profile "follows on" from the primary profile. Their shotpoint number sequences should also go in the same direction, either both increasing or both decreasing.

Select the primary and then the secondary profile, then click the Join Profiles   menu/toolbar button to enter Join Profiles mode.

As you move the mouse in the viewer window, the nearest shotpoint on the primary or secondary profiles will be highlighted.
First, select the shotpoint on the primary profile at which the join will take place.
Then select the first shotpoint on the secondary profile to include in the joined profile:

After you have selected both shotpoints, a PRMEDIT dialogue box will be displayed for you to confirm the shotpoints selected. The dialogue also displays the calculated SP difference between the selected secondary shotpoint, and the projected shotpoint value from the primary profile. The SP Difference is the value subtracted from the shotpoints in the secondary profile to make them join smoothly with the primary profile. You can edit this difference if you believe that it requires adjustment.

Click OK to perform the join:

To exit from Join Profiles mode, and save the joined profile to the current temporary LOC file, click the Join Profiles   menu/toolbar button again to un-toggle it.


8. Split Profile

Split a profile into two parts using the Split Profile  option.

Select the profile to split and click the Split Profile   menu/toolbar button to enter Split Profile mode.

As you move the mouse in the viewer window, the nearest shotpoint on the current profile will be highlighted. The highlighted shotpoint will be where the second line-part starts. Click to select the shotpoint to split at.

In the displayed PRMEDIT dialogue, Select names for parts A and B of the profile, confirm the shotpoint at which to start part B, and specify the number of shotpoints overlap to use.

Click OK to perform the split.

To exit from Split Profile mode, and save the split profiles to the current temporary LOC file, click the Split Profile   menu/toolbar button again to un-toggle it.


9. Renumber by SP and distance

Sometimes you may have incomplete information about the shotpoints along a line. For example, the line may have significant curvature or "bends" which have to be digitised, to define the track of the line, but the added nodes then lack shotpoint information.

This option will renumber all the shotpoints between two specified control points, using linear interpolation by distance. First, the total distance between the two control points is calculated, by summing the lengths of the segments in between. Then the shotpoint at each node is calculated by linear interpolation, according to the node's distance from the end points.

Before you start, make sure that shotpoint labels are turned on, so that you can see all the shotpoint numbers on the line. Select Options|Edit Parameters|, or press on the main toolbar, then page to the page "Line node (shotpoint) drawing" and set the node label properties.

Select the required profile and press

Set the first control point, by moving the cursor and clicking when the required point is highlighted. Set the second control point in a similar way. After the second point is selected, an edit window will appear in which you can enter the required shotpoint numbers for the chosen points. Note that shotpoints outside the chosen segment will be unaltered.

Press OK to apply the changes. You can now repeat the sequence - select another pair of points - edit the numbers - OK, until all the shotpoints are as you want them. Press again to exit.


10. Location Geometry Test

The Location Geoemtry Test is accessed from the Check menu in LOCPREP. It can be used to check the internal integrity of the location data. This option will not perform a reconciliation of location data with seismic data - use Florence and Zebedee to do this.

Select the Parameters-Edit  menu to set the parameters for the error checking:

Report All Profile Statistics
YES - include all profiles in output report
NO - exclude profiles where no errors found from output report

The following parameters specify the types of errors to include in the report:

Repeated Profile Names - YES/NO - check for profile names which are duplicated elsewhere in the LOC file

Bad XY Coordinates - YES/NO - check for missing/invalid XY coordinate for each record. This option must be set to YES for the Point-to-Point errors to be performed.

Bad LL Coordinates - YES/NO - check for missing/invalid latitude/longitude coordinate for each record.

Point-to-Point Distance - YES/NO - check that each location point is within a specified threshold of the average point-to-point distance between points

Distance Error Threshold - specify a percentage of the average distance between points calculated for each profile. Points which fall outside this percentage difference will be flagged as errors.

Point-to-Point Angle - YES/NO - check that each location point is within a specified threshold of the average direction of the profile.

Angle Threshold - specify an angle. Points which differ from the average direction by more than this angle will be flagged as errors/

SP Sequence Errors - YES/NO - check for repeated and non-sequential shotpoints

Max Errors per Profile - specify the maximum number of errors per profile. If more than this number of errors are found for a profile they will not be reported and the report skips to the next profile


Click the Run Geometry Test  menu to perform the test.
The output can be viewed in two formats:


11. Metadata

Metadata means "data about data". In the case of UKOOA or LOC files, the metadata consist of supplemetary textual information that may be placed in the file header. The UKOOA 84 standard allows for general infomation in header records identied by the prefix "H26" and this is the convention adopted in LOCPREP. As the input file is edited in Locprep, information about each stage of the editing process is added to an internal list. On saving the file, the metadata are added to the output file header. This enables later users of the file to identify what changes have been made.

Changing the metadata prefix
The default prefix in Locprep is "H26M". This enables records added by Locprep to be distinguished easily from general header records added by other applications, which may carry essential information. This prefix is set in the LOCPREP.INI file [labels] section as "metadata prefix=H26M" so that it can be changed if necessary. However, the first character of the prefix must always be "H" to enable applications to recognise the metadata as header records.


12. Error and Warning Messages

The following error and warning messages are produced by LOCPREP

Switch display coordinate system to display file?
The file you are attempting to open contains a different coordinate system to the current display parameters. Standard "UKOOA"-type locations files usually contain both projected and unprojected coordinates, so you can switch between the two coordinate systems within LOCPREP (see General Parameters - Coordinate Display). However, some locations files only contain a single coordinate system. This message warns you that the display coordinate system is being changed in order to display the current file.


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Copyright © Lynx Information Systems Ltd 2013