CFD Utilities Files

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!
   program gen_to_grid
!
!  Description:
!
!     This is a belated attempt to automate what has hitherto been done one line
!  segment at a time to turn a finely discretized capsule generatrix, containing
!  a number of critical points such as shoulder step corners that need to be
!  preserved into a computational surface grid form of the geometry. The curv-
!  ature-based redistribution of CAPSULE_GRID can easily be thwarted by such
!  geometric features.  A common example is the need to split the generatrix at
!  the top of a shoulder seal step.  That corner marks the end of the forebody
!  part of the generatrix and the beginning of the aft body part.  Since these
!  two parts are usually gridded separately, the step corner is not seen and is
!  thus not clustered as it needs to be.  Capturing of a parachute lid corner is
!  another example.
!
!     The CAPSULE_GRID work-around is to provide it with a generatrix that is
!  discretized in the desired surface grid form and will be retained exactly
!  through appropriate choice of the ni_forebody and ni_aft_body control inputs.
!  This ancillary utility is intended to simplify preparation of that carefully
!  discretized form of the generatrix, undoubtedly through trial and error.
!
!  Strategy:
!
!     A control table scheme is employed.  The first two table columns contain
!  the (x,y) coordinates of all critical points to be preserved exactly.  The
!  further columns contain the type of point distribution for each line segment,
!  the desired number of points, and first and last arc-length increments that
!  may or may not be used, depending on the distribution type.
!
!  Sample Input:
!
!     Enter the control table as the first command line argument (not on stdin).
!  Following the header lines, the table needs to be numeric and complete, so
!  unused entries on the last line are entered as 99 to indicate "irrelevant."
!  The critical points are expected to be ordered nose to tail.
!
!     RevB.generatrix.tecplot.dat
!     -1 = high-end clustering (ds2); 0 = uniform; 1 = low-end clustering (ds1)
!      2 = 2-sided clustering (ds1 and ds2);
!      3 = curv.-based redistribution; ds1, ds2 = power, ismooth = 0.5, -3 say;
!      4 = redistribute with same relative distrib. as the following file(s).
!     x              y             type   npts    ds1          ds2
!     0.             0.            3       199    0.5          -3
!     0.91790681     2.31206956    2        31    6.57237E-03  0.001
!     0.9967         2.280235      2         7    0.001        0.001
!     0.9967         2.2730        2       251    0.001        0.0015
!     2.5759         1.292678      2        29    0.0015       0.003
!     2.66407        1.17542       2       127    0.003        0.015
!     3.816567       0.43700926    2        52    0.015        9.77421E-03
!     3.892025       0.087901      0        10    99           99
!     3.895          0.0           99       99    99           99
!
!     The initial generatrix data are expected to be in the file on line 1.  It
!  may include optional header lines. Any third column of (zero?) z coordinates
!  is ignored.  Once the table has been prepared, the (x,y) columns of critical
!  points should be extracted and plotted as symbols on the generatrix curve.
!  These critical points will replace the nearest points within the generatrix
!  data, from which each line segment is drawn for redistribution according to
!  the specs. on the first line of a pair of critical point control lines.
!
!     The example does not include a type 4 segment, but if it did, the name
!  of the file containing the desired relative distribution would appear below
!  the 4 = ... header line. Any further type 4 file names would follow in order.
!  Any such files should omit header lines and include a third column of z
!  coordinates (most likely zeros).  E.g.,
!
!     nose-xyz-given.dat
!     -1 = high-end clustering (ds2); 0 = uniform; 1 = low-end clustering (ds1);
!      2 = 2-sided clustering (ds1 and ds2);
!      3 = curvature-based redistrib.; ds1, ds2 = power, ismooth = 0.5, -3 say;
!      4 = redistribute with same relative distrib. as the following file(s).
!     RevB.111.fore.dat
!             x              y                type  npts    ds1          ds2
!             0.             0.               4      229    99           99
!       9.9670000E-01 2.285189859737330e+00   99      99    99           99
!
!  Note that, because of the way the earlier 3-space utility MORPH_LINE_SEGMENT
!  was remodularized, the user here is prompted for any type 4 files containing
!  desired relative point distributions. Cut and paste RevB.111.fore.dat in this
!  example.
!
!  Output:
!
!     The output gridded form of the generatrix is named surface_grid_xy.dat
!  or surface_grid_xyz.dat depending on a prompt for whether to include a z = 0.
!  column as expected by the Hypgen volume-gridding scheme.
!
!  History:
!
!     06/01/2023  D.A.Saunders  Initial design.
!     06/07/2023    "      "    Completion of initial implementation & testing.
!     06/08/2023    "      "    The curvdis2 option needs two more controls.
!                               Make use of the unused ds1, ds2 inputs.
!                               0.5 and -3 are recommended for the forebody of
!                               a typical sphere/cone.
!     10/31/2023    "      "    Rude surprise for Halloween: Kaelan Hansson
!                               found that gfortran does not support getarg,
!                               advising that Fortran 2003 and later provides
!                               this similar intrinsic:
!                               get_command_argument (number [, value, length,
!                                                     status]) instead.
!     11/19/2023    "      "    Retrofitted the type 4 option to impose the
!                               relative distribution of an indicated segment.
!                               Any reasonable point count may be specified.
!     04/27/2024    "      "    Since the Hypgen script expects three-column
!                               xyz input, provide for including z = 0. in the
!                               output (or not).
!
!  Author:  David Saunders, AMA, Inc. at NASA Ames Research Center, CA.
!
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