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*=======================================================================
*
* PGSBOX 7.4 - draw curvilinear coordinate axes for PGPLOT.
* Copyright (C) 1997-2021, Mark Calabretta
*
* This file is part of PGSBOX.
*
* PGSBOX is free software: you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published
* by the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* PGSBOX is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with PGSBOX. If not, see http://www.gnu.org/licenses.
*
* Author: Mark Calabretta, Australia Telescope National Facility, CSIRO.
* http://www.atnf.csiro.au/people/Mark.Calabretta
* $Id: fscan.f,v 7.4 2021/01/31 02:24:52 mcalabre Exp $
*=======================================================================
*
* FSCAN defines an azimuth/frequency coordinate system for PGSBOX.
*
* Given:
* OPCODE I Transformation code:
* +2: Compute a set of pixel coordinates that
* describe a path between this and the
* previous pair of world coordinates
* remembered from the last call with
* OPCODE = +1 or +2.
* +1: Compute pixel coordinates from world
* coordinates.
* 0: Initialize.
* -1: Compute world coordinates from pixel
* coordinates.
*
* NLC I Number of elements in NLCPRM (=1).
*
* NLI I Number of elements in NLIPRM (=1).
*
* NLD I Number of elements in NLDPRM (=7).
*
* NLCPRM C(NLC)*1 Character array (ignored).
*
* NLIPRM I(NLI) Integer array (ignored).
*
* Given and/or returned:
* NLDPRM D(NLD) Double precision coefficients (see below).
*
* WORLD D(2) World coordinates. WORLD(1) and WORLD(2)
* are the longitude in degrees, and
* log10(frequency/1Hz).
* Given if OPCODE > 0, returned if OPCODE < 0.
*
* PIXEL D(2) Pixel coordinates.
* Given if OPCODE < 0, returned if OPCODE > 0.
*
* CONTRL I Control flag for OPCODE = +2 (ignored, always
* set to 0 on return).
*
* CONTXT D(20) Context elements (ignored).
*
* Returned:
* IERR I Status return value:
* 0: Success.
* 1: Invalid coordinate transformation
* parameters.
*
* Notes:
* The NLDPRM array is constructed as follows:
* - (1) Axis 1 reference pixel coordinate
* - (2) Axis 2 reference pixel coordinate
* - (3) Axis 1 reference pixel value (degree)
* - (4) Axis 2 reference pixel value
* - (5) Axis 1 coordinate increment (degree/pixel)
* - (6) Axis 2 coordinate increment
* - (7) Rate of change of NLDPRM(4) with x-pixel
*
*=======================================================================
SUBROUTINE FSCAN (OPCODE, NLC, NLI, NLD, NLCPRM, NLIPRM, NLDPRM,
: WORLD, PIXEL, CONTRL, CONTXT, IERR)
*-----------------------------------------------------------------------
INTEGER CONTRL, IERR, NLC, NLD, NLI, NLIPRM(NLI), OPCODE
DOUBLE PRECISION CONTXT(20), NLDPRM(NLD), PIXEL(2), S, WORLD(2)
CHARACTER NLCPRM(NLC)*1
*-----------------------------------------------------------------------
IERR = 0
IF (OPCODE.GT.0) THEN
* Compute pixel coordinates from world coordinates.
PIXEL(1) = NLDPRM(1) + (WORLD(1) - NLDPRM(3))/NLDPRM(5)
S = NLDPRM(4) + PIXEL(1)*NLDPRM(7)
PIXEL(2) = NLDPRM(2) + (WORLD(2) - S)/NLDPRM(6)
CONTRL = 0
ELSE IF (OPCODE.EQ.0) THEN
* Initialize.
IF (NLC.LT.1 .OR. NLI.LT.1 .OR. NLD.LT.7) IERR = 1
IF (NLDPRM(5).EQ.0D0) IERR = 1
IF (NLDPRM(6).EQ.0D0) IERR = 1
IF (NLDPRM(7).EQ.0D0) IERR = 1
CONTRL = 0
ELSE IF (OPCODE.EQ.-1) THEN
* Compute world coordinates from pixel coordinates.
WORLD(1) = NLDPRM(3) + NLDPRM(5)*(PIXEL(1) - NLDPRM(1))
WORLD(2) = NLDPRM(4) + NLDPRM(6)*(PIXEL(2) - NLDPRM(2)) +
: PIXEL(1)*NLDPRM(7)
ELSE
IERR = 1
END IF
RETURN
END
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