; $Id: tri_surf.pro,v 1.9 2001/01/15 22:28:14 scottm Exp $
;
; Copyright (c) 1993-2001, Research Systems, Inc.  All rights reserved.
;	Unauthorized reproduction prohibited.

FUNCTION TRI_SURF, z, x, y, REGULAR = regular, XGRID=xgrid, $
	XVALUES = xvalues, YGRID = ygrid, YVALUES = yvalues, $
	GS = gs, BOUNDS = bounds, NX = nx0, NY = ny0, $
	MISSING = missing, EXTRAPOLATE = extrapolate, LINEAR=linear
;+
; NAME:
;	TRI_SURF
;
; PURPOSE:
;	This function Interpolates a regularly or irregularly gridded
;	set of points with a smooth quintic surface.
;
; CATEGORY:
;	Mathematical functions, Interpolation, Surface Fitting
;
; CALLING SEQUENCE:
;	Result = TRI_SURF(Z [, X, Y])
;
; INPUTS: 
;	X, Y, Z:  arrays containing the X, Y, and Z coordinates of the 
;		  data points on the surface. Points need not be 
;		  regularly gridded. For regularly gridded input data, 
;		  X and Y are not used: the grid spacing is specified 
;		  via the XGRID and YGRID (or XVALUES and YVALUES) 
;		  keywords, and Z must be a two dimensional array. 
;		  For irregular grids, all three parameters must be
;		  present and have the same number of elements. 
;
; KEYWORD PARAMETERS:
;  Input grid description:
;	REGULAR:  if set, the Z parameter is a two dimensional array 
;		  of dimensions [N,M], containing measurements over a 
;		  regular grid. If any of XGRID, YGRID, XVALUES, YVALUES 
;		  are specified, REGULAR is implied. REGULAR is also 
;		  implied if there is only one parameter, Z. If REGULAR is 
;		  set, and no grid (_VALUE or _GRID) specifications are 
;		  present, the respective grid is set to (0, 1, 2, ...). 
;	XGRID:    contains a two element array, [xstart, xspacing], 
;		  defining the input grid in the X direction. Do not
;		  specify both XGRID and XVALUES. 
;	XVALUES:  if present, XVALUES[i] contains the X location 
;		  of Z[i,j]. XVALUES must be dimensioned with N elements. 
;	YGRID:    contains a two element array, [ystart, yspacing], 
;		  defining the input grid in the Y direction. Do not
;		  specify both YGRID and YVALUES. 
;	YVALUES:  if present, YVALUES[i] contains the Y location 
;		  of Z[i,j]. YVALUES must be dimensioned with N elements. 
;
;  Output grid description:
;	GS:	  If present, GS must be a two-element vector [XS, YS],
;		  where XS is the horizontal spacing between grid points
;		  and YS is the vertical spacing. The default is based on
;		  the extents of X and Y. If the grid starts at X value
;		  Xmin and ends at Xmax, then the default horizontal
;		  spacing is (Xmax - Xmin)/(NX-1). YS is computed in the
;		  same way. The default grid size, if neither NX or NY
;		  are specified, is 26 by 26. 
;	BOUNDS:   If present, BOUNDS must be a four element array containing
;		  the grid limits in X and Y of the output grid:
;		  [Xmin, Ymin, Xmax, Ymax]. If not specified, the grid
;		  limits are set to the extent of X and Y. 
;	NX:       The output grid size in the X direction. NX need not
;	  	  be specified if the size can be inferred from GS and
;		  BOUNDS. The default value is 26.
;	NY:       The output grid size in the Y direction. See NX. 
;
;  Others:
;       EXTRAPOLATE: If set, extrapolate the surface to points outside
;		the convex hull of input points.  Has no effect if
;		input points are regularly gridded.
;	MISSING: If set, points outside the convex hull of input points
;		are set to this value.  Default is 0.  Has no effect
;		if input points are regularly gridded.
;	LINEAR:  If set, linear interpolation, rather than quintic is
;		used.  Gradient estimates are not used.  This is faster
;		and numerically stable, but does not extrapolate.
;
; OUTPUTS:
;	This function returns a two-dimensional floating point array
; 	containing the interpolated surface, sampled at the grid points.
;
; RESTRICTIONS:
;	The output grid must enclose convex hull of the input points.
; PROCEDURE:
;	This routine is similar to MIN_CURVE_SURF but the surface
;	fitted is a smooth surface, not a minimum curvature surface.  This
;	routine has the advantage of being much more efficient
;	for larger numbers of points.
;
;	The built-in IDL routines TRIANGULATE and TRIGRID(/QUINTIC) are
;	used.
;
; EXAMPLES:
; Example 1: Irregularly gridded cases
;	Make a random set of points that lie on a gaussian:
;	  n = 15				;# random points
;	  x = RANDOMU(seed, n)
;	  y = RANDOMU(seed, n)
;	  z = exp(-2 * ((x-.5)^2 + (y-.5)^2)) 	 ;The gaussian
;
; 	get a 26 by 26 grid over the rectangle bounding x and y:
;	  r = TRI_SURF(z, x, y)	;Get the surface.
;
; 	Or: get a surface over the unit square, with spacing of 0.05:
;	  r = TRI_SURF(z, x, y, GS=[0.05, 0.05], BOUNDS=[0,0,1,1])
;
; 	Or: get a 10 by 10 surface over the rectangle bounding x and y:
;	  r = TRI_SURF(z, x, y, NX=10, NY=10)
;
; Example 2: Regularly gridded cases
;	Make some random data
;	  z = randomu(seed, 5, 6)
;
;	interpolate to a 26 x 26 grid:
;	  CONTOUR, TRI_SURF(z, /REGULAR)
;
; MODIFICATION HISTORY:
;	DMS, RSI, October, 1993.  Written.
;	DMS, RSI, Jan, 1996. Added LINEAR keyword.
;-


ON_ERROR, 2
s = size(z)		;Assume 2D
nx = s[1]
ny = s[2]

reg = keyword_set(regular) or (n_params() eq 1)

if n_elements(xgrid) eq 2 then begin
	x = findgen(nx) * xgrid[1] + xgrid[0]
	reg = 1
endif else if n_elements(xvalues) gt 0 then begin
	if n_elements(xvalues) ne nx then $
		message,'Xvalues must have '+string(nx)+' elements.'
	x = xvalues
	reg = 1
endif

if n_elements(ygrid) eq 2 then begin
	y = findgen(ny) * ygrid[1] + ygrid[0]
	reg = 1
endif else if n_elements(yvalues) gt 0 then begin
	if n_elements(yvalues) ne ny then $
		message,'Yvalues must have '+string(ny)+' elements.'
	y = yvalues
	reg = 1
endif

if reg then begin
	if s[0] ne 2 then message,'Z array must be 2D for regular grids'
	if n_elements(x) ne nx then x = findgen(nx)
	if n_elements(y) ne ny then y = findgen(ny)
	x = x # replicate(1., ny)	;Expand to full arrays.
	y = replicate(1.,nx) # y
	endif

n = n_elements(x)
if n ne n_elements(y) or n ne n_elements(z) then $
	message,'x, y, and z must have same number of elements.'

if n_elements(bounds) lt 4 then begin	;Bounds specified?
	xmin = min(x, max = xmax)
	ymin = min(y, max = ymax)
	bounds = [xmin, ymin, xmax, ymax]
	endif

TRIANGULATE, x, y, tr, b

if n_elements(gs) lt 2 then begin	;GS specified?  No.
    if n_elements(nx0) le 0 then nx = 26 else nx = nx0 ;Defaults for nx and ny
    if n_elements(ny0) le 0 then ny = 26 else ny = ny0
    gs = [(bounds[2]-bounds[0])/(nx-1.), $
	   (bounds[3]-bounds[1])/(ny-1.)]
  endif else begin			;GS is specified?
    if n_elements(nx0) le 0 then $
	nx = ceil((bounds[2]-bounds[0])/gs[0]) + 1 $
    else nx = nx0
    if n_elements(ny0) le 0 then $
	ny = ceil((bounds[3]-bounds[1])/gs[1]) + 1 $
    else ny = ny0
  endelse


if N_ELEMENTS(missing) le 0 then missing = 0

if KEYWORD_SET(linear) then $
    return, TRIGRID(x,y,z, tr, gs, bounds, MISSING=missing)

if KEYWORD_SET(extrapolate) then $
    return, TRIGRID(x,y,z, tr, /QUINTIC, gs, bounds, $
		    MISSING=missing, EXTRAPOLATE=b)

return, TRIGRID(x,y,z, tr, /QUINTIC, gs, bounds, MISSING=missing)
end