CFD Utilities Files

The interp3d utilities perform interpolations, intersections, or other
calculations involving 3-space data (mostly curves and surfaces).  Some
of the curve methods really belong in interplib (1-D) because they involve
arc length as the single independent variable, but they remain here for
historical reasons.

Most of these precede the ADT (alternating digital tree) search packages
that are now recommended for efficient interpolation within volume meshes,
structured or not.

Most of these routines arose from development of the rapid grid generators
CH_GRID (the gridding portion of wing/body shape optimization code SYN87SB)
and the surface paneling package AEROSURF (the geometry engine for the
multiblock full-configuration shape optimization code SYN107MB).  Others
arose from line-of-sight calculations applied to CFD solutions for hyper-
sonic reentry vehicles.

bilincut.f         Parametric bilinear analogue of PLBICUT (z given x, y)
furthest_point.f90 3-space line pt. "most inside" a convex regular surface
inside_outside.f90 Is a point "inside" or "outside" a structured surface?
intsec4.f          Intersect a curve & regular surface in 3-spc. (PLBICUBE)
intsec5.f          Bilinear form of INTSEC4 using PBILINT, not PLBICUBE
intsec6.f90        Multipatch form of INTSEC5: ADT techniques/minimization
intsec6.f90.two_point_lines  1st INTSEC6 form for 2 pt. straight line cases
intsec8.f90        Variant of INTSEC6 for a triangulated surface; see usintec
intsec9.f90        Use instead of intsec6 to handle nonconvex surfaces
lcsint3d.f         Variant of TABLE3 using LCSFIT, not linear interpolation
line_surface.f90   Find up to two intersections of line with closed surface
peval3.f           Evaluate curve x,y,z vs. t via spline coefs. from PFIT3
pfit3.f            Conventional spline coefs., x,y,z vs. t on a 3-sp. curve
plbicut.f          Find (u,v) & corresp. z matching x, y on a 3-sp. surface
pleval.f           Companion to PLFIT for rectilinear curves, 2 or 3 space
plfit.f            Poorly-named arc-length utility for 1|2||3-space curves
plscrv3d.f         Parametric local spline interpolation on a 3-spc. curve
plscurve.f         Used by MODGRID4 (gridlib); not as efficient as PLSCRV3D
plsfit3d.f         Analogue of PLSFIT (interp2d); lacks PLSCRV3D's derivs.
plsintyz.f         Interpolate y, z for given x(s) on an (x,y,z) curve
plxcut3d.f90       Find arc-length coresp. to a given x on a 3-space curve
quad_interp.f90    Interpolation within a quadrilateral from vertex data
smoothxyz.f        Gaussian kernel-based smoothing of noisy curve | surface
table3.f           Trilinear interp. in rectangular table, in function form
tri_line.f90       Intersect line thru (xt,zt) _|_ y = 0 w/ 3-spc. triangle
trilint.f          Part of RIPPLE3D approach to searching a structured grid
usintsec.f90       Uses intsec8 twice to handle a nonconvex triangulated surface
wbintr.f           Compute intersectn. betwn. "wing", "body" regular meshes

06/25/21           Added plxcut3d variant of plxcut for application to a
                   3-space curve in CAPSULE_GRID.
03/05/22           USINTSEC intersects a line/curve with a triangulated surface
                   that may have concavities.  INTSEC8 has a slight ADT change.