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3d Ray Tracing
3d Ray Tracing Program Arguments
This program uses the
dds I/O system
to set arguments for controlling
the program.
Arguments can be passed via the command line,
input data dictionary, or input data. The command line has the highest
presidence in the case of ambiguous definitions.
And it may be useful to use this presidence rule to override erroneous
header information from seismic data sets.
Argument Summary
for program d3depth2time and d3time2depth:
-
[help=] [ -h | ? | -help ]
- [in= dds_vel_dict]
- [norms= ray_starting_info]
- [time_section= out_travel_time] [verbose=]
- [save_rays= yes | no]
- [axis= x y z ]
- [size.x= Number_of_Pts_in_x_direction]
- [delta.x= Increment_between_Pts_in_X]
- [origin.x= X_axis_Origin]
- help= causes this help message to be printed. The "help"
information is also printed if any of the flags "-h ? or -help" are present.
- in= dds_vel_dict identifies the velocity file data dictionary.
The parameters describing the velocity model such as the number of increments
in each direction (size.x= nx, size.y=ny, and size.z=nz) can be set on the
command line, in the
dds
dictionary, or in the data file if the data format
supports the necessary parameters. The number of increments in each direction,
and the size of the increments in each direction MUST be specified somewhere
in the dds hierarchy. If the origin is not defined to dds, then this program
assumes that the origin is (0,0,0).
- norms= surface_at_depth identifies the name of the file specifying the
input surface and the surface normal directions in
PtNorm format.
- time_section= time_file_name identifies the output
PtNorm
file created by tracing
rays and computing travel time along the rays.
This file also contains the ray directions at the
surface and can be used as starting positions for tracing rays
back to the original surface.
- save_rays=y causes to program to compute and output ray
paths into the file
- ray.trajectory - ascii format
- real.rayparms.rs - gocad++ format
- axis= x y z causes the labels "x", "y", and "z" to be applied to the
three integer coordinate axes of the velocity model.
Other possible values for labels are: axis = East North Depth, or axis=
x y t.
- size.x= nx specifies that the velocity model has nx values in the "x" direction.
- size.y= ny specifies that the velocity model has ny values in the "y" direction.
- size.z= nz specifies that the velocity model has nz values in the "z" direction.
- delta.x= dx specifies that the size of the increments between stations of
the velocity model in the "x" direction is dx (and similarly in the y and z
directions)
- origin.x= x0 specifies the origin of the velocity model in the "x" direction (and similarly in the y and z directions)
The relationship between positions given by the PtNorms file and
stations in the velocity model is given by formulae of the form:
ix = Int((x-x0)/dx) +1
rx = (x-x0-(ix-1)*dx)/dx
where x is the x location of a ray, ix is the maximum index of any velocity
station having a smaller x value than the ray, ix+1 is the minimum index of
any velocity station
having an x coordinate larger than the ray,
and rx is the relative weighting factor for linearly interpolating between
v(ix) and v(ix+1). That is, v(x)= v(ix)*(1-rx)+ v(ix+1)*rx. The program
uses trilinear interpolation to obtain values of velocity between
velocity stations in the 3d velocity field and bilinear interpolation
to obtain gradient values. That is, the program uses the above formula
to interpolate in however many dimensions that are appropriate.
Last Modified: .
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dvasicek@trc.amoco.com
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