spectrum.h

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/*                      S P E C T R U M . H
 * BRL-CAD
 *
 * Copyright (c) 2004-2006 United States Government as represented by
 * the U.S. Army Research Laboratory.
 *
 * This library 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 2.1 of
 * the License, or (at your option) any later version.
 *
 * This library 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
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this file; see the file named COPYING for more
 * information.
 */
/** @addtogroup libmultispectral */
/*@{*/
/** @file spectrum.h
 *
 *  A header file containing data structures to assist with
 *  recording spectral data.
 *  The overall notion is that each spectral sample should be
 *  as compact as possible (typically just an array of power levels),
 *  with all the context stored in one place.
 *
 *  The context is kept in an 'bn_table' structure, and
 *  the data for one particular sample are kept in an 'bn_tabdata'
 *  structure.
 *  tabdata.h provides the data structures,
 *  librt/tabdata.c provides the routines.
 *
 *  The contents of the spectral sample in val[j] are interpreted
 *  in the interval (wavel[j]..wavel[j+1]).
 *  This value could be power, albedo, absorption, refractive index,
 *  or any other wavelength-specific parameter.
 *
 *  For example, if the val[] array contains power values, then
 *  val[j] contains the integral of the power from wavel[j] to wavel[j+1]
 *
 *  As an exmple, assume nwave=2, wavel[0]=500, wavel[1]=600, wavel[2]=700.
 *  Then val[0] would contain data for the 500 to 600nm interval,
 *  and val[1] would contain data for the 600 to 700nm interval.
 *  There would be no storage allocated for val[2] -- don't use it!
 *  There are several interpretations of this:
 *      1)  val[j] stores the total (integral, area) value for the interval, or
 *      2)  val[j] stores the average value across the interval.
 *
 *  The intervals need not be uniformly spaced; it is acceptable to
 *  increase wavelength sampling density around "important" frequencies.
 *  This will undoubtably complicate certain functions.
 *
 *  By convention, wavelength is stored in nanometers as an integer,
 *  and power is stored in Watts.
 *
 *  Wavelength Units -
 *      cm = 10** -2 m  centimeters
 *      mm = 10** -3 m  milimeters
 *      um = 10** -6 m  micrometers, or microns
 *      nm = 10** -9 m  nanometers
 *
 *  The Spectrum in nm -
 *      < 10 nm                 X-Rays
 *      10 to 390               Ultraviolet
 *      390 to 770              Visible
 *      770 to 1500             Near IR
 *      1500 to 6,000           Middle IR       (includes 3-5 um band)
 *      6,000 to 40,000         Far IR          (includes 8-12 um band)
 *      40,000 to 1,000,000     Extreme IR
 *      > 10**6 nm              Microwaves      (300 GHz to 300 MHz)
 *      > 10**9 nm              Radio waves     (300 MHz and down)
 *
 *  It is tempting to store the wavelength in nanometers as an integer,
 *  but that might preclude very narrow-band calculations, such as might
 *  be required to study a single spectral line,
 *  and it might also preclude future extensions to X-rays.
 *  Because there are likely to be very few bn_table structures
 *  in use, the extra storage isn't a likely problem.
 *  The worst effect of this decision will be floating-point grunge
 *  when printing wavelengths, e.g. 650nm might print as 649.99nm.
 *  On the other hand, non-integer values might make it difficult to
 *  determine if two wavelengths from different curves were the "same",
 *  without introducing a wavelength "tolerance" notion.  Ugh.
 *
 *  @author
 *      Michael John Muuss
 *
 *  @par Source
 *      The U. S. Army Research Laboratory
 *      Aberdeen Proving Ground, Maryland  21005-5068  USA
 *  $Header: /cvsroot/brlcad/brlcad/include/spectrum.h,v 14.9 2006/09/18 05:24:07 lbutler Exp $
 */

#include "common.h"

#include "bn.h"
#include "raytrace.h"

/*
 * Routines
 */
RT_EXPORT BU_EXTERN(void                        rt_spect_make_CIE_XYZ,
                    (struct bn_tabdata          **x,
                     struct bn_tabdata          **y,
                     struct bn_tabdata          **z,
                     const struct bn_table      *tabp));

RT_EXPORT BU_EXTERN(void                        rt_spect_black_body,
                    (struct bn_tabdata          *data,
                     double                     temp,
                     unsigned int               n));
RT_EXPORT BU_EXTERN(void                        rt_spect_black_body_fast,
                    (struct bn_tabdata          *data,
                     double                     temp));

RT_EXPORT BU_EXTERN(void                        rt_spect_reflectance_rgb,
                    (struct bn_tabdata          *curve,
                     const float                rgb[3]));

/*@}*/
/*
 * Local Variables:
 * mode: C
 * tab-width: 8
 * c-basic-offset: 4
 * indent-tabs-mode: t
 * End:
 * ex: shiftwidth=4 tabstop=8
 */

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