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tdotri

Orders the triangles in a triangle list for proper rendering (for use with selected TDPACK routines).

Available in version 4.3.1 and later.

Prototype

	function tdotri (
		rtri   [*][10] : float,    
		ntri       [1] : integer,  
		rtwk       [*] : float,    
		order_flag [1] : integer   
	)

	return_val [*] :  integer

Arguments

rtri

A float input/output array, dimensioned mtri x 10, in which a list of triangles has been stored.

ntri

An input/output integer specifying the number of triangles currently in the triangle list. This value should have been set by a previous routine like tdmtri.

rtwk

A float scratch array of length at least mtri x 2.

order_flag

An integer scalar indicating one of three ways in which triangles are to be sorted.

Return value

An integer array of length mtri that will contain a permutation of the integers from 1 to ntri.

Description

This routine is part of the low-level TDPACK package, which is a group of Fortran and C callable routines for projecting objects from a 3-dimensional coordinate system having U, V, and W axes to a 2-dimensional projection plane having X and Y axes and/or for drawing the projections of those objects. This can be referred to somewhat loosely as "drawing objects in three dimensions".

Given a list of ntri triangles in the array rtri and scratch array rtwk, this function determines the order in which the triangles are to be rendered and returns a permutation of the integers from 1 to ntri defining that permutation.

Please see the documentation on TDOTRI for a full description of this function.

Examples

The following code produces a sample 3D scatter plot:

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"

; 
; Function for generating random data.
;
function dsrnd1(ifrst,nextn)
begin
  MPLIER = 16807
  MODLUS = 2147483647
  MOBYMP = 127773
  MOMDMP = 2836
  JSEED  = 123456789

  if (ifrst .eq. 0) then
    nextn = JSEED
    ifrst = 1
  end if

  hvlue = nextn / MOBYMP
  lvlue = nextn % MOBYMP
  testv = MPLIER*lvlue - MOMDMP*hvlue

  if (testv .gt. 0) then
    nextn = testv
  else
    nextn = testv + MODLUS
 end if

  return((1.*nextn)/(1.*MODLUS))
end


begin
 N       = 1331
 NEAREST =  500
 MTRI    = 150000
 FARTHER = N - NEAREST

;
; Create our input and work arrays.
;
  x = new(N,float)
  y = new(N,float)
  z = new(N,float)
  rtri = new((/MTRI,10/),float)
  rtwk = new((/MTRI,2/),float)

;
; Fill up the dummy input arrays.
;
  ifrst = 0
  nextn = 0
  do i = 0,N-1
    x(i) = dsrnd1(ifrst,nextn)    
    y(i) = dsrnd1(ifrst,nextn)
    z(i) = dsrnd1(ifrst,nextn)    
  end do

;
;  Specify the reference point from which we want to find the NEAREST
;  nearest points.
;
  px = 0.5
  py = 0.5
  pz = 0.5

  wks = gsn_open_wks("ps","scatter")  

;
; Set some TDPACK parameters and initialize. These four are viewport
; specifiers.
;
  tdsetp("VPB", 0.09)
  tdsetp("VPT", 0.99)
  tdsetp("VPL", 0.11)
  tdsetp("VPR", 1.00)

  tdinit((/4.6, 3.0, 3.3/), (/0.5, 0.5, 0.5/), (/0.5, 0.5, 2.7/), 0.)

;
;  Set up some colors using the standard TDPACK entry for that.
;
  tdclrs(wks, 1, 0., 0.8, 8, 37, 8)

;
;  Define style indices for shades of gray, green, and red.
;
  tdstrs(1,  8, 37,   8,  37, 1, 1, 0, 0.05, 0.05, 0.)
  tdstrs(3,  8, 37,  68,  97, 1, 1, 0, 0.05, 0.05, 0.)
  tdstrs(4,  8, 37,  98, 127, 1, 1, 0, 0.05, 0.05, 0.)

;
;  Store the indices of the nearest points in npts and the complement
;  of that set (with respect to the entire input dataset) in mpts.
;
  npts = new(NEAREST,integer)
  mpts = new(FARTHER,integer)

  npts(0) = shgetnp(px,py,pz,x,y,z,0)
  do i=2,N
    if (i .le. NEAREST) then
      npts(i-1) = shgetnp(px,py,pz,x,y,z,1)
    else
      mpts(i-1-NEAREST) = shgetnp(px,py,pz,x,y,z,1)
    end if
  end do

;
;  Plot the near points in green.
;
  ntri = 0
  dotsize = 0.02
  do i = 0, NEAREST-1
    tdmtri(-5, (/x(npts(i)-1), y(npts(i)-1), z(npts(i)-1)/), dotsize, \
           rtri, ntri, 4, (/0.,0.,0./),(/1.,1.,1./))
  end do

;
;  Plot the farther points in gray.
;
  do i = 0, FARTHER-1
    tdmtri(-5, (/x(mpts(i)), y(mpts(i)), z(mpts(i))/), dotsize, \
           rtri, ntri, 1, (/0.,0.,0./),(/1.,1.,1./));
  end do

;
;  Mark the reference point in red.
;
  tdmtri(-5,(/px,py,pz/),1.2*dotsize,rtri,ntri,3,(/0.,0.,0./),(/1.,1.,1./))

;
;  Order and draw triangles.
;
  itwk = tdotri(rtri, ntri, rtwk, 0)
  tddtri(wks,rtri, ntri, itwk)

;
;  Draw a box around the perimeter.
;
  tdgrds(wks,(/0., 1., 0./), (/1., 0., 1./), (/-1., -1., -1./),11,0)
  tdgrds(wks,(/0., 1., 0./), (/1., 0., 1./), (/-1., -1., -1./),11,1)

  frame(wks)

end