Traceprep TPUtl Utilities Package

Processing Utilities

Version1.25 (back to TracePrep main index)

Introduction

Configuration

TPUtl Processes

Program Messages

Introduction

The TracePrep TPUtl package is a set of utilities for simple post-stack seismic data processing, including time variant filtering and scaling, shifting, resampling, muting and insertion of shotpoints, XY coordinates and labels into trace headers. These processes are typically used on raw stacks, or after vectorising paper seismic sections, to prepare the data for workstation loading.

Configuration

To install the TPUtl package, run the TracePrep setup program. TPUtl comprises a dynamic link library TPUtl.DLL and a corresponding INI file TPUtl.INI. These two files are added to the Lynx system directory (LynxSys) at installation. The help file (this file) is added to the docs subdirectory of LynxSys. For TracePrep to recognise the new package, the installation adds an entry to the TracePrep.INI file [packages] section, e.g.

[packages]
TPUtl=vvvv

where vvvv is the version number of the TPUtl module, found in the [lynx] section of TPUtl.INI.

The [config] section in TPUtl.INI contains module constants which can be edited manually, or through the LEAConfig application

Processes

AGC - Automatic Gain Control

Automatic Gain Control (AGC) will boost the amplitude of weak parts of a trace, relative to stronger parts. A running window is passed down the input trace, centred on each output sample position. For each output sample on the trace the average absolute amplitude of neighbouring input samples from the window is calculated. The number of samples to average is determined by the window length parameter. The centre of the window is placed at the output sample position, so thet the output samples S at position i are given by :

Si = ki * Ri

and

ki = P * L / sum( |Rj| )  j = i - L/2 to i + L/2

where

ki is a variable scale factor
Si is the output sample
Rj is an input sample
L is the length of the window in samples
P is the desired absolute amplitude

The shorter the AGC window the more rapid the response to average amplitude fluctuations and hence the more these fluctuations are smoothed out.

Process ID - TracePrep standard process ID

Process title - A brief description of an instance of the process

Output Level
(type single, limits 0.0 to 10000.0)
This corresponds to the desired absolute amplitude P, above

Window length, msec
(type single, limits 1.0 to 10000.0)
This corresponds to the window length L, above, but is in milliseconds, not samples.

LBINSERT - Trace label insert

Inserts text labels into Lynx trace file headers, for later plotting. This process is retained for compatibility with the Lynx 3-S LBINSERT program and plotting with SeisPlot via the 3-S TRCPLOT program. The labels inserted by this process cannot be retained in SEG-Y output format, which does not have a place for labels in the trace header.

Process ID - TracePrep standard process ID

Process title - A brief description of an instance of the process

Label file specification
(type option, TraceFile, Other )
If "TraceFile", the file in which the labels will be supplied will be named identically to the trace file. TracePrep searches first for a trace auxiliary .TAX file and then, if that is not found, for an old-style 3-S format .LBL file (see 3-S program LBINSERT),

If a .TAX file is present, the labels must be inserted into it first, using TaxEdit.

If "Other" is entered here, then the file name for the label file must be provided below.

The FileName field specifies the name of a .TAX auxiliary file or .LBL file containing the labels for this trace file.
(type filename )

Shotpoint source
(type option, Regular, Auxiliary) specifies the source of the shotpoint information, when shotpoint positions are used for the labels. If a 3-S .LBL file is used, the labels will always have shotpoint positions. In a .TAX file the label positions can be specified by shotpoint, trace, cdp or distance.

"Regular" - Shotpoints are regularly spaced. The shotpoints are calculated from the trace number, first shotpoint and shotpoint increment stored in the trace file header.

"Auxiliary" - for each trace, shotpoints are read from the auxiliary shotpoint field in the trace headers. Use this option if irregular shotpoints have been inserted into the headers using SPINSERT.

Existing labels
(type option, Clear, Keep) what to do with labels which already exist in trace headers

"Clear" - clear existing labels

"Keep" - keep existing lables and add new labels. Note that a Lynx format trace header can contain a maximum 4 labels of up to 29 characters each.

LENGTH - Change length of traces

Changes the length , by adding or removing samples, at the start or end of a trace.

Process ID - TracePrep standard process ID

Process title - A brief description of an instance of the process

Add or remove samples
(type option, Add, Remove )
"Add" - adds zero sample values, according to the criteria below

"Remove" - removes samples.

msec to add or remove
(type single, limits 100.0 to 10000.0)
The time in msec to add or remove, from the beginning or end of the trace. This will be rounded to the nearest whole number of samples.

Apply at trace
(type option, Start, End)
"Start" - add or remove samples at the start of the trace

"End" - add or remove samples at the end of the trace.

MUTE - Trace Mute

Trace muting zeros the input trace samples between a specified begin-mute and end-mute time. It is mainly used for eliminating unwanted noise above the water bottom in marine sections and applying the "run-in" and "run-out" mutes where the stack fold of the data varies. In TracePrep, the end mute time can be used for other purposes, such as a floating datum for applying time variant filtering or scaling and for applying space variant time shifts.

Process ID - TracePrep standard process ID

Process title - A brief description of an instance of the process

Mute action
(type option, Insert,Extract,Apply,InsertApply)
Action to take on each trace

Insert - Threshold or File derived mutes are inserted into the trace headers

Extract - Threshold mutes or trace header mutes are written to the file - see Mute File parameter. This option can only be used if the Source of Mute is "Header" or "Threshold".

Apply - the mutes are applied to the traces, i.e. sample amplitudes between the start and end mute times are zeroed.

InsApply - both Insert and Apply actions are carried out.

Source of Mute
(type option, Header, File, Threshold)
The source of the mute data

Header - read the mutes previously inserted in the trace headers

File - read the mutes from a file

Threshold - calculate a "threshold mute", that is, the end mute time is a point obtained by measuring the sample amplitudes from the beginning of the trace and determining the point at which the amplitude exceeds a threshold.

Mute File specification
(type option, As tracefile, Other)
As tracefile - the name of the file containing the mute information is the same as the trace file, but with an extension .MTE or .TAX. The program looks first for an .MTE file, old-style Lynx 3-S mute file. If it cannot find it, an attempt is made to get the mute information from the .TAX trace auxiliary file

Other - specify the .MTE file or a trace auxiliary file .TAX file containing the mutes for the input trace file.

Warning - If the Mute Action is "Extract", existing mute values in the specified file will be completely overwritten.

The .MTE format is provided for backward compatibility with the older Lynx 3-S format, as used by the the current version of SSV and MS-DOS programs MTPICK, TRCMUTE and TRCFIX. The MTE format is an ASCII text file containing entries of the form

trace starttime endtime
where trace is the trace sequence number, starttime and endtime are the start and end times for the mute, in milliseconds at trace. The values on each line should be separated by at least one blank. Mute times at trace numbers between the entries will be linearly interpolated.

For example:

1 0 2200
48 0 120
557 0 160

This will apply a lead-in mute taper, from 2200 msec on trace 1 to 120 msec on trace 48. The mute slopes down to 160 msec at trace 557.

FileName
(type file name)
The name of the MTE or TAX file containing space variant mute data.

Threshold %
(type single, limits 0.0 to 250.0)
If the type of mute is "Threshold", set this parameter to the desired threshold level, as a percentage of the trace RMS amplitude, at which the mute will end

Set back msec
(type single, limits -100.0 to 100.0)
The time in msec entered here is subtracted from the mute stop time determined by the threshold.

Taper msec
(type single, limits - 0.0 to 1000.0)

A linear taper of this length is applied back from mute stop time towards the start time. This will smooth the appearance of a mute which cuts through the trace data where the amplitude is high.

RESAMP - Resample traces in time

Use this process for redetermining the time sample interval of the input data. The number of samples per trace will be altered by this process. Note that resampling to a larger sampling interval (smaller number of samples per trace) may result in the loss of some higher frequency information.

Process ID - TracePrep standard process ID

Process title - A brief description of an instance of the process

Sample interval option
(type option, Absolute, Relative, )
The output sample interval can be specified either as

Absolute - The desired New sample interval is entered below. Depending on the input sample interval, the output samples will be interpolated according to the ratio between the actual input sample interval derived from the output of the previous process and the desired output sample interval.entered below. If you don't know what the input sample interval is, but merely want to multiply it by some factor, use Relative.

Relative - The desired output sample is entered as a multiple of the actual input sample interval, in the "multiply s.i. by" field below.

New sample interval
(type single, limits 0.25 to 24.0)
The sample interval, in milliseconds, when the Absolute sample interval option above

Multiply s.i. by
(type single, limits 0.1 to 1000)
The multiplier for the sample interval, when the Relative sample interval is selected above. e.g. If the input sample interval is 4.0 milliseconds and you want an output sample interval of 2.0 milliseconds, enter 0.5.

Apply anti alias
(type option, Yes, No, )
Yes to apply a high cut filter to the input trace, before re-sampling. This option should only be selected when the output sample interval is to be greater than the input sample intervaland when there is significant frequency content in the input data at the output Nyquist frequency.

High cut / Nyquist
(type single, limits 0.1 to 1.0)
The cutoff frequency of the anti-alias filter, if selected, as a fraction of the Nyquist frequency 1.0/(2dT), for the input sample interval dT.

For example, for 2 millisecond input sample interval, the Nyquist frequency is 1000 / (2.0 x 2), or 250Hz. If the output sample interval is to be 4 milliseconds, for which the Nyquist frequency is 125Hz, the anti alias filter should ideally ensure that there is negligible frquency content at 125Hz. In many cases, the data are being subsampled because there is not much energy at high frequencies, in whic case an anti-alias filter may not be necessary.

RESPACE - Resample traces in space

Redetermines the actual trace spacing "on the ground", i.e. the CMP spacing on post-stack data. This will increase or decrease the number of traces in the trace file. Useful for

Process ID - TracePrep standard process ID

Process title - A brief description of an instance of the process

Trace spacing
(type option, Absolute, Relative )
The output trace interval can be specified in two ways :-

Absolute - The desired output trace spacing is entered below. Depending on the input trace spacing, the output will be interpolated according to the ratio between the actual input trace spacing derived from the output of the previous process and the desired output trace spacing, entered below. If you don't know what the input trace spacing is, but merely want to multiply it by some factor, use Relative.

Relative - The desired output trace spacing is entered as a multiple of the actual input trace spacing, in the "multiply spacing" field below.

Multiply spacing
(type single, limits 0.1 to 1000)

New Spacing
(type single, limits 1.0 to 1000.0)
The desired trace spacing, in metres or feet, when using the Absolute trace spacing option above. This, of course, assumes that the trace spacing is correctly set in the input file header.

Note that if the spacing is being increased, spatial antil-aliasing may be required, in which case precede the RESAMP process with a MIX or XTFILTER process.

Interpolation No. of traces
(type long integer, limits 1 to 6)
The number of input traces used in interpolating the output. A horizontal sinc function interpolator having 1 to 6 coefficients is used to calculate each sample on the output trace. The default (4) will give good results in most cases.

SHIFT - Shift traces in time

The SHIFT process applies a constant or space varying time shift to the input traces.

Process ID - TracePrep standard process ID

Process title - A brief description of an instance of the process

type of shift
(type option, Constant, Xvariant)
The applied shift can be shift constant in X (space), or X variant

Constant - enter the required time shift below

XVariant - specify the source of the shift data below

time shift msec
(type single, limits -5000.0 to 5000.0)
The time shift in milliseconds to be applied to the traces. See also sign of shift below - this determines whether the shift will be up or down.

shift source
(type option, Auxiliary, MTE,LagA,LagB,Mute1,Mute2,RecDelay,Static )
The source of the time shift data for the XVariant type of shift.

File Options

Auxiliary - use shift data from the trace file's .TAX auxiliary file. The data will be read from the horizon specified below in "horizon name".

MTE - use shift data from a Lynx MTE file, which specifes trace number vs shift

Trace header options - for a fuller explanation of the trace header slots, see SEGY/Lynx trace file specification.

LagA - use shift from trace header bytes 105-106 "LagA time break"

LagB - use shift from trace header bytes 107-108 "LagB time break"

Mute1 - use shift from trace header bytes 111-112 "Mute time--start"

Mute2 - use shift from trace header bytes 113-114 "Mute time--end"

RecDelay - use shift from trace header bytes 109-110 "Delay recording time"

TotalStatic - use shift from trace header bytes 103-104 "Total static applied"

add datum msec
(type single, limits -5000.0 to 5000.0)
Specify a datum to add to the time shifts read from the file. The sign of shift will be applied before the datum is added.

multiplier
(type single, limits 0.0001 to 10000.0)
Specify a multiplier for the shifts. This will be applied to the shifts after the sign and datum parameters. The applied shift will be given by

dT = m * ( (f * sign) + datum)

where
f is the time shift for the trace, taken from the shift source
sign is +1.0 for Up and -1.0 for Down shift
datum is the added datum
m is the multiplier

horizon name
(type string )
The name of the picked event, to be used for the time shifts, in the [horizon] section of the trace auxiliary file

direction of shift
(type option, Up, Down, )
Specifies the direction of the time shifts.

Up - postive time shifts result in trace data that are "pulled up", i.e. events appear earlier in time on the output traces.

Down - postive time shifts result in trace data that are "pushed down", i.e. events appear later in time on the output traces.

pad traces msec
(type single, limits -5000.0 to 5000.0)
Pad the output traces with zero samples at the beginning, or end, before shifting.

Zero no padding is applied. Data on the input trace which are shifted out of the trace's time range will be lost.

+nnnn to pad the end of each trace with nnnn msecs of zeros. When the direction of shift is down, this will preserve samples which would otherwise be shifted off the end of the trace.

-nnnn to pad the beginning of each trace with nnnn msecs of zeros. When the direction of shift is up, this will preserve samples which would otherwise be shifted off the beginning of the trace.

Action
(type option, Shift, Blip, Both)
Shift - apply the specified shift to the traces

Blip - place a "blip", i.e. change the amplitude of a single sample, on the trace at the time corresponding to the shift. The amplitude of the blip to be determined below.

Both - Shift the trace and then insert a blip, as above.

Blip amplitude
(type single, limits -10000.0 to 10000.0)
The amplitude of the blip to be inserted by Blip or Both Action option above.

SPINSERT - Shotpoint Insert

Use SPINSERT to insert shotpoint numbers into each indvidual trace's header. For SEG-Y files, this is the only way that shotpoint information can be stored. To extract SP information from headers, use the XYCOORD process and ignore the associated XY coordinate information.

A Lynx format trace file has three ways of storing shotpoint information:-

  1. The first shotpoint and shotpoint increment per trace are stored in the file header. If shotpoints are regular, there is usually no need insert shotpoints. Use a utility such as TRACEDMP or TRACEFIX to change the header values
  2. The trace header shotpoint field SPNo, which holds a floating point shotpoint number for every trace - this corresponds to the SEG-Y trace header field bytes 17-20, with the important difference that the SEG-Y trace header shotpoint number is an integer. Interpolated shotpoints are stored in this header field.
  3. The inserted shotpoint field SPAux, which holds the floating point shotpoint defined at a particular trace on the profile. This enables both irregular and discontinuous shotpoint sequences to be handled correctly. Trace header fields in between the inserted positions may be zero or undefined.

A "pure" SEGY format trace file has only one way to store shotpoint information - in trace header bytes 17-20, as a 4-byte integer number. SPINSERT will insert the interpolated or calculated shotpoints into this header field. Note that if the shotpoint increment, per trace, is not an integer, the SEGY shotpoint numbers will be rounded to the nearest integer

A "Lynx SEGY" format trace file, that is a SEG-Y file produced by TracePrep, or by the older 3-S SEGSAVE program, also stores the first shotpoint and shotpoint increment per trace in the binary file header.

Process Parameters

Process ID - TracePrep standard process ID

Process title - A brief description of an instance of the process

Insert mode
(type option, file, computed )
this determines how the shotpoints will be calculated

File mode - shotpoints are read from a text table, prepared in advance. Each line of the table has a trace number followed by the shotpoint that is associated with that trace. The trace number must be an whole number with no decimal point whilst the shotpoint number must be a number with a decimal point. The trace numbers must be in the correct order. The table can be prepared as an .SPT file by a text editor such as Windows Notepad, or as an auxiliary file in TaxEdit.

Computed mode - shotpoints are calculated from the trace number combined with the first shotpoint and shotpoint interval entered below

Shotpoint file spec
(type option, Tracefile, Other )
This field is active if File mode is selected above.

If "TraceFile", the file in which the shotpoint data are supplied will be named identically to the trace file. For example if the tracefile is MYFILE.TR1 then the shotpoint file would be MYFILE.SPT, or MYFILE.TAX. TracePrep searches first for an .SPT file and then, if that is not found, for a trace auxiliary .TAX file

If a .TAX file is present, the labels must be inserted into it first, using TaxEdit.

If "Other" is entered here, then the file name for the label file must be provided below.

FileName
(type string)
The name of the .SPT or .TAX file, if different from the trace file name. Ignore this field if the shotpoint or auxiliary file name is the same as the trace file name.

The SPT File is an ASCII Lynx 3-S SPINSERT file. This usually has a filename that is the same as the trace file name with an extension .SPT. The trace number and shotpoint number should be separated by spaces.

Example of .SPT format shotpoint file, for shotpoints to be inserted at traces 1, 20, 40 and 54 :-

1 25.0
20 30.0
40 35.0
54 40.0

First SP
(type single, limits -10000.0 to 10000.0)
Shotpoint corresponding to trace 1

SP Interval
(type single, limits -10000.0 to 10000.0)
Shotpoint increment, per trace. The inserted shotpoint number will be calculated as

SP = First_SP + (itr - 1) x SP_Interval

A Note about Shotpoints

Irregular shotpoints are used when location data, or intersection labels, are to be inserted in the trace headers and the spacing between shotpoints is not a constant number of traces. They can also be used if you want to plot a particular pattern of plotted shotpoints in order to duplicate the annotation on an original section.

Discontinuous shotpoints can be used when two seismic profiles, with arbitrary shotpoint ranges, are to be joined and the shotpoint numbers on the original location data are to be preserved.

A shotpoint is a floating point number, associated with a trace, used to relate the trace to a particular location on the ground. Every seismic profile's traces therefore need to be assigned unique shotpoint numbers. These may change regularly or irregularly along the profile, sometimes with discontinuities or repeated ranges.

All shotpoints must be numeric. Sometimes shotpoint numbers will have alphabetic suffixes, particularly when there are many output stacked traces for each integral change in the shotpoint number. These should be replaced by using the approriate decimal shotpoint increment

On many stack sections, shotpoint numbers increment regularly at some multiple, or sub multiple of the trace spacing, so that the shotpoint number for any trace is easily calculated. Sometimes shotpoint sequences will be irregular, i.e. the number of traces per shotpoint varies along the line, or discontinuous, as in Figure 1, where different shotpoint ranges join.

Shotpoint discontinuities must be consistently handled. Where a discontinuity occurs in the shotpoints, the nearest two traces on either side of the discontinuity should each be correctly labelled, and have corresponding location points on the map.

x..........................xx....................x.......
1                        100 250                 350					shotpoint number

Figure 1. A discontinuous shotpoint range

The various combinations are summarised below.

Case  Discontinuous Irregular Remedy
a) NO NO Use regular SP numbering
b) YES NO Insert shotpoints at each end of the line and in pairs on either side of discontinuities
c) NO YES Insert shotpoints at each end of the line and at sufficiently close intervals to define properly the variations in the SP-trace relationship
d) YES YES as for (b), but also insert additional shotpoints as for (c)

TVFILTER - Time Variant Bandpass Filter

A recursive Butterworth filter is applied in a smoothly time varying manner. The filter bandwidth is specified at a number of time control points. In between the control point times the filter high and low cut frequencies are interpolated from the nearest two control points. The filter can be applied relative to a fixed or variable datum.

Process ID - TracePrep standard process ID

Process title - A brief description of an instance of the process

Type of Datum
(type option, Zero, Mute, Fixed, )
Zero - the time variant filtering, specified below, will be relative to time zero

Mute - the time variant filtering will be relative to the end-mute time stored in the trace header. If the end-mute time represents the water bottom, for example, the time variant filter characteristics will "track" the water bottom. This is particularly useful in situations where the water bottom time varies a lot across the section.To use this option, you must set the mutes in the trace headers of the input traces.

Datum - the time variant filtering will be relative to a fixed datum, entered below

datum time msec
(type single, limits -1000.0 to 20000.0)
The time value, relative to which the time-frequency pairs are calculated. For example, if the first pair is 1500.0, 65.0, and the datum is 1000.0, then the frequency 65Hz will apply at 2500.0 msec (=1000 + 1500).

Filter time
(type single, limits 0.0 to 20000.0)
Control point - filter time in milliseconds

Filter Frequency
(type single, limits -10000.0 to 10000.0)
Control point - filter frequency in Hz

The remaining filter control points are entered as time-frequency pairs

At times less than the first control point time, the filter cut-offs are equal to their values at the first control point. At times greater than the last control point, the filter cut-offs are equal to their values at the last control point.. Frequencies between control points are linearly interpolated from the control points on either side, in time.

If the frequencies at a control point are both zero, the control point is ignored.

The filter slopes are fixed at 24 dB/Octave for zero phase and 12 dB/Octave for minimum phase.

TVSCALE - Time Variant Scaling

Apply time variant scaling to the input traces

Process ID - TracePrep standard process ID

Process title - A brief description of an instance of the process

Type of Datum for times
(type option, Zero, Mute, Datum)
Zero - the time variant scaling, specified below, will be relative to time zero

Mute - the time variant scaling will be relative to the end-mute time stored in the trace headers. If the end-mute time represents the water bottom, for example, the scaling characteristics will "track" the water bottom. This is particularly useful in situations where the water bottom time varies a lot across the section. To use this option, you must set the mutes in the trace headers of the input file.

Datum - the time variant scaling will be relative to a fixed datum, entered below

datum time msec
(type single, limits -1000.0 to 20000.0)
The time value, relative to which the time-scale pairs are calculated. For example, if the first pair is 1500.0, 2.0, and the datum is 1000.0, then the scale factor 2.0 will be applied at 2500.0 msec.


(type single, limits 0.0 to 20000.0)
Time value 1. At times less than this time, the scale will be equal to scale factor 1 below


(type single, limits -10000.0 to 10000.0)
scale factor 1. The trace sample values at this time will be multiplied by this scale factor.


The remaining time-amplitude pairs are entered here. Unused time-scale pairs shoud have their time values set to less than the time of the last time-scale pair to be used.

If the trace end time is greater than the time of the last time-scale pair used, the scale of this time-scale pair will be applied don to the last sample on the trace.

XYCOORD - Insert and extract X-Y Coordinates

Insert or extract X-Y coordinates to or from trace headers.

Process ID - TracePrep standard process ID

Process title - A brief description of an instance of the process

Action
(type option, Insert, Extract )
for the current trace, either insert or extract X-Y coordinates fom trace header

Insert - for each input trace, reads the trace's shotpoint, then finds the nearest shotpoints, on either side, in the location file. The X and Y values are interpolated from these shotpoints and placed in the trace header.

Extract - for each trace, the shotpoint, X and Y coordinates are written to the location file

Location File type
(type option, LocFile, Auxiliary)
The location file is the file used as the source or destination for the X and Y coordinate data

LocFile - the XY file is a Lynx .LOC file (UKOOA type file). Each XY coordinate pair is read from, or written to the file together with the corresponding shotpoint number. Note that if the LOC file contains Lat/Lon values, these will be ignored when inserting and can be zero or blank. When extracting into a LOC file, the Lat and Lon values in each of the newly generated records will be zero.

Auxfile - the XY data are in the trace auxiliary file in the [location] section, which is of the form

[location]

xcoord=coordtype

where coordtype is chsen from trace, shotpoint, cdp or distance. This will determine the units of key in the list of X-Y coordinates following

key1=xxxxxx1,yyyyyy1

key2=xxxxxx2,yyyyyy2

where the keys are in units of coordtype and xxxxx and yyyyy are the corresponding x and y coordinates at that point.

FileName
(type string )
The file name for the location file, if different from the trace file name. Otherwise, leave this field blank

Shotpoint source
(type option, Regular, Header, Auxiliary)
The source of the shotpoints from the trace file.

Regular - standard shotpoints from the trace file header, with a regular SP increment

Header - use shotpoints previously stored in the Shotpoint field, bytes 17-20 of the trace header. Irregular or discontinous shotpoints can be placed there with SPINSERT.

XY trace header fields
(type option, Source,Group)
Determines which pair of trace header XY coordinate fields to use.

Source - use the seismic source coordinates

Group - use the coordinates for the centre of the geophone or hydrophone group

Already existing Line
(type option, Delete,Append)
When exxtracting, i.e. copying data from ta seismic file to a .LOC file this determines what to do if the Line name already exists in the file.

Delete - removes the existing line's records from the .LOC file, before copying in the new data

Append - appends the new data to the existing line, sorts the records by shotpoint and and rewrites back to the .LOC file. If the line parts have overlapping shotpoint ranges, or discontinuous or non-monotonic shotpoints, it is better to give the line parts different names and merge the location data using LOCPREP.

NOTES

1) The SSV vectorising program stores raster coordinates for the start of each trace in the SX and SY fields. These can be overwritten in later processing.

2) For marine data, it's possible that a location file may specify "antenna" position, that is, the postion of the radio or satellite antenna abord the shooting vessel. In this case, the receiver group's position will have to be compensated according to the direction of the cable and the offset between the antenna and the centre of the cable. This is a non-trivial calculation.

Program Messages and Errors

AGC process fault An exception occurred while applying AGC

Label insert fault An exception occurred due to bad data in label strings or out of range shotpoint information.

Label insertion file error An error occurred while attempting to read label information from a label or auxiliary file.

Error applying Mute An exception occurred while trying to apply mutes.

Error reading mute file An error occurred while attempting to read label information from a mute or auxiliary file

cannot extract from mute file the Extract option specified is not allowed in file mode.

no TVF points found In the TVFILTER process, no valid filter points were specified.

Respace sync error a program fault occurred.

Error shifting traces An error occurred while attempting to apply a shift to a trace. The shift may be out of range or the trace may contain extreme amplitude values.

error reading shift file An error occurred while attempting to read shift information from an MTE or auxiliary file.

Error reading shotpoint file An error occurred while attempting to read shotpoint information from an auxiliary file.

Error inserting shotpoint an exception occurred while inserting shotpoints

TVF times must increase In the TVFILTER process, the time was not monotonically increasing in the time-filter points specification.

Time variant filter error an exception occurred while applying the time variant filter

Time variant scaling error an exception occurred while applying the time variant scaling

Error reading XY data An error occurred while attempting to read XY information from an auxiliary file or .LOC file.

Error inserting XY data

XY data file not found The specified XY data file was not found

X coord numeric conversion error An X-coordinate in the XY data file contained non-numeric characters.

Y coord numeric conversion error An Y-coordinate in the XY data file contained non-numeric characters.

no coordinate data found The XY data file contained no coordinate data.

error writing XYs to file

error reading XYs from file

LCT .LOC index file not found The .LOC file's index file was missing. Run the Locprep utility to gnerate a new index file.

LCT file error or out of date The .LOC file's index file had an earlier date than the .LOC file, or is corrupted.

Line not found in location file The specified line name was not found in the .LOC file.

.LOC file record conversion error The .LOC file's contained missing or corrupted data

Auxiliary (TAX) file error codes

-1 file doesn't exist
-2 not enough items in comma delimited list after the "=" character
-3 bad data values found after the "=" character
-4 no data found