/usr/share/gnudatalanguage/coyote/inside.pro is in gdl-coyote 2016.11.13-2.
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; NAME:
; INSIDE
;
; PURPOSE:
;
; The purpose of this function is to indicate whether a specified
; 2D point is inside (returns a 1) a specified 2D polygon or outside
; (returns a 0).
;
; AUTHOR:
;
; FANNING SOFTWARE CONSULTING
; David Fanning, Ph.D.
; 1645 Sheely Drive
; Fort Collins, CO 80526 USA
; Phone: 970-221-0438
; E-mail: david@idlcoyote.com
; Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
;
; CATEGORY:
;
; Utility.
;
; CALLING SEQUENCE:
;
; result = INSIDE(x, y, xpts, ypts)
;
; INPUTS:
;
; x: A scalar or vector of the x coordinates of the 2D point(s) to check.
; y: A scalar or vector of the y coordinates of the 2D point(s) to check.
; xpts: The x coordinates of the 2D polygon.
; ypts: The y coordinates of the 2D polygon.
;
; OUTPUTS:
;
; result: A scalar or vector set to 1 if the point is inside the polygon and to
; 0 if the point is outside the polygon.
;
; KEYWORDS:
;
; INDEX: An output keyword. If set to a named variable, will return the indices
; of the X and Y points that are inside the polygon.
;
; ALGORITHM:
;
; Based on discussions on the IDL newsgroup (comp.lang.idl-pvwave) and
; discussed here:
;
; http://www.idlcoyote.com/tips/point_in_polygon.html
;
; Primarily the work of B�rd Krane and William Connelly.
;
; MODIFICATION HISTORY:
;
; Written by: David W. Fanning, 4 September 2003.
; Vectorized the function in accord with William Connelly's suggestions 24 July 2005. DWF.
;-
;******************************************************************************************;
; Copyright (c) 2008, by Fanning Software Consulting, Inc. ;
; All rights reserved. ;
; ;
; Redistribution and use in source and binary forms, with or without ;
; modification, are permitted provided that the following conditions are met: ;
; ;
; * Redistributions of source code must retain the above copyright ;
; notice, this list of conditions and the following disclaimer. ;
; * Redistributions in binary form must reproduce the above copyright ;
; notice, this list of conditions and the following disclaimer in the ;
; documentation and/or other materials provided with the distribution. ;
; * Neither the name of Fanning Software Consulting, Inc. nor the names of its ;
; contributors may be used to endorse or promote products derived from this ;
; software without specific prior written permission. ;
; ;
; THIS SOFTWARE IS PROVIDED BY FANNING SOFTWARE CONSULTING, INC. ''AS IS'' AND ANY ;
; EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES ;
; OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT ;
; SHALL FANNING SOFTWARE CONSULTING, INC. BE LIABLE FOR ANY DIRECT, INDIRECT, ;
; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED ;
; TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; ;
; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ;
; ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT ;
; (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS ;
; SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. ;
;******************************************************************************************;
FUNCTION Inside, x, y, xpts, ypts, INDEX=index
On_Error, 1
sx = Size(xpts)
sy = Size(ypts)
IF (sx[0] EQ 1) THEN NX=sx[1] ELSE Message, 'X coordinates of polygon not a vector.'
IF (sy[0] EQ 1) THEN NY=sy[1] ELSE Message, 'Y coordinates of polygon not a vector.'
IF (NX EQ NY) THEN N = NX ELSE Message, 'Incompatable vector dimensions.'
; Close the polygon.
tmp_xpts = [xpts, xpts[0]]
tmp_ypts = [ypts, ypts[0]]
; Set up counters.
i = indgen(N)
ip = indgen(N)+1
nn = N_Elements(x)
X1 = tmp_xpts(i) # Replicate(1,nn) - Replicate(1,n) # Reform([x],nn)
Y1 = tmp_ypts(i) # Replicate(1,nn) - Replicate(1,n) # Reform([y],nn)
X2 = tmp_xpts(ip) # Replicate(1,nn) - Replicate(1,n) # Reform([x],nn)
Y2 = tmp_ypts(ip) # Replicate(1,nn) - Replicate(1,n) # Reform([y],nn)
; Calculate the dot and cross products of the point to neighboring points in the polygon.
; Calculate the tangent of the angle between the two nearest adjacent points. If the point
; is outside the polygon, then summing over all possible angles will give a small number,
; in this case less than an arbitrary 0.1.
dp = X1*X2 + Y1*Y2 ; Dot-product
cp = X1*Y2 - Y1*X2 ; Cross-product
theta = Atan(cp,dp)
ret = Replicate(0L, N_Elements(x))
i = Where(Abs(Total(theta,1)) GT 0.01, count)
IF (count GT 0) THEN ret(i)=1
; Make this a scalar value if there is only one value.
IF (N_Elements(ret) EQ 1) THEN ret=ret[0]
; If the index keyword is set, then return indices.
IF (Arg_Present(index)) THEN ret=(Indgen(/Long, N_Elements(x)))(Where(ret eq 1))
RETURN, ret
END
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