This process creates a new volume with modified headers by executing a formula at each input trace, using one or more horizon values and/or header values from the input volume.
For more information on operators, variables and math functions usable in the formula, see Functions and Variables for Math Expressions.
This process will not allow you to alter the fundamental headers that define a volume (e.g. NS, DT, and DELRT for all volumes; INLINE and CROSSLINE for 3D volumes; EP and TRACR for shot/channel volumes; etc).
NS, DT, and DELRT are modified only by using one of the processes designed to change the length or sampling of traces (such as Trace Pad, Trace Shift, Volume Resample, Velocity Conversion, etc). Depending on the situation, you may be able to change the other restricted headers with the Reassign Geometry Headers process.
Other fundamental headers that cannot be modified inside Insight (such as INLINE/CROSSLINE for a 3D volume) can be changed during SEG-Y export, if necessary.
For pre-migration 2D volumes (i.e. shot records), where the formula refers to a 3D horizon, there are several possible sources of X/Y location to use to extract horizon values:
- CMP X/Y location (CDPX/CDPY headers)
- Receiver location (GX/GY headers)
- Source location (SX/SY headers)
- In the Process tab, click the Add icon and select New Process.
- Select Header Maths and type a name for the process.
- In the Details Panel, select the input volume.
- Select Input Horizons and its Properties by clicking on the Add icon on the right.
Missing Values: If the horizon values is missing, there are two ways to handle the issue:
- Set headers to 0; or
- Raise an error.
- In the Formulae section, choose a Header and type the formula to execute.
As a result of this process, a new volume is available in the Volume tab.
Note: Click the Help icon to read more about this process including built-in variables, operators, constants, functions and examples (see also Functions and Variables for Math Expressions).
Add new header
- In the Formulae section, click the Header search box.
- Scroll to the bottom of the header list.
- Click the New header... button.
- A Create new header window will appear, enter the header name and description.
- Click OK to add or click cancel.
Scaled fields can be identified in the Trace Headers table below where the 'Scalar' column is defined. These fields will be scaled automatically when used as a variable in a Header Maths formula or when storing the result. That is, the real, human, floating-point value is what will be used in the formula, and what your formula should produce.
For example, if we want to change a volume to have a minimum receiver depth (GELEV) of 5m, we should use a formula like:
GELEV if (GELEV 5, 5, GELEV)
Assuming that your receiver depth header is set correctly in the first place, this will give the correct result regardless of the value of SCALEL.
DUG Insight uses SEG-Y rev 1 headers in its internal data format (see Trace Header Variables for Math Expressions). The table lists the purpose to which Insight puts those headers, assuming that the data was loaded from field tapes in Insight, and that the header values have not since been modified. If Insight does not use a header for any particular purpose, its SEG-Y rev 1 description is given.
Your data, of course, might have values in these headers that have different meanings.