commit 718193214d261fa686c6c39fac5049df1759ae72
parent 14f76f7e274d6364db4fb5daeb5c72ff36522f35
Author: Vincent Forest <vincent.forest@meso-star.com>
Date: Thu, 4 Jun 2020 15:23:05 +0200
Update the man page with the new spectral integration
Diffstat:
2 files changed, 91 insertions(+), 41 deletions(-)
diff --git a/doc/htrdr-image.5.txt b/doc/htrdr-image.5.txt
@@ -30,25 +30,33 @@ thus ignored as well as empty lines. The first valid line stores 2 unsigned
integers that represent the image definition, i.e. the number of pixels per
line and per column. Then each line stores 8 pixel components.
-If the image is a regular rendering in the visible part of the spectrum, the
-pixel components are actually 4 pairs of floating points data representing the
-pixel color encoded in the CIE 1931 XYZ color space and the per radiative path
-computation time. The first, second and third pair encode the estimated
-integrated radiance in W.sr^-1.m^-2 of the X, Y and Z pixel components,
-respectively. The first value of each pair is the expected value of the
-estimated radiance while the second one is its associated standard deviation.
-The fourth pair saves the estimate in microseconds of the per radiative path
-computation time and its standard error.
-
-If the image is an infrared rendering, the first and second pixel components
-store the expected value and the standard error, respectively, of the
-estimated brightness temperature in Kelvin. The third and fourth component
-save the expected value and standard deviation of the pixel radiance in
-W.sr^-1.m^-2.nm^-1. The fifth and sixth pixel components are unused. Finally
-the last 2 pixel components save, as for a regular rendering, the estimate in
+If the image is a regular rendering in the visible part of the spectrum
+(*-s* _cie_xyz_ option in *htrdr*(1)), the pixel components are actually 4
+pairs of floating points data representing the pixel color encoded in the CIE
+1931 XYZ color space and the per radiative path computation time. The first,
+second and third pairs encode the estimated integrated radiance in W/sr/m^2 of
+the X, Y and Z pixel components, respectively. The first value of each pair is
+the expected value of the estimated radiance while the second one is its
+associated standard deviation. The fourth pair saves the estimate in
microseconds of the per radiative path computation time and its standard
error.
+If the image is an infrared rendering (*-s* *lw*=_wlen-min_,_wlen_max_ option
+in *htrdr(1)), the first and second pixel components store the expected value
+and the standard error, respectively, of the estimated brightness temperature
+in Kelvin. The third and fourth components save the expected value and standard
+deviation of the pixel radiance that is either an integrated radiance in
+W/sr/m^2 or a spectral radiance in W/sr/m^2/nm whether this radiance is
+computed for a spectral range or for one wavelength. The fifth and sixth pixel
+components are unused. Finally the last 2 pixel components save, as for a
+regular rendering, the estimate in microseconds of the per radiative path
+computation time and its standard error.
+
+If it was generating from a shortwave rendering (*-s*
+*sw*=_wlen-min_,wlen-max_ option in *htrdr*(1)) the image is formatted as in
+longwave rendering mode exepted that the first and second pixel components are
+unused since no brightness temperature was evaluated in shortwave.
+
Pixels are sorted line by line, with the origin defined at the top left corner
of the image. With an image definition of N by M pixels, with N the number of
pixels per line and M the overall number of lines in the image, the first N
diff --git a/doc/htrdr.1.txt.in b/doc/htrdr.1.txt.in
@@ -30,7 +30,13 @@ SYNOPSIS
DESCRIPTION
-----------
*htrdr* is an image renderer of scenes composed of an atmospheric gas mixture,
-clouds, and a ground. Images can be rendered in the visible or the infrared
+clouds, and a ground. It evaluates the intensity incoming on each pixel of the
+sensor array. The underlying algorithm is based on a Monte-Carlo method: it
+consists in simulating a given number of optical paths originating from the
+camera, directed into the atmosphere, taking into account light absorption and
+scattering phenomena.
+
+Images can be rendered in the visible or the infrared
part of the spectrum. It uses spectral data that should be provided for the
pressure and temperature atmospheric vertical profile [1] (*-a* _atmosphere_),
the liquid water content in suspension within the clouds stored in a *htcp*(5)
@@ -44,27 +50,28 @@ whose materials are listed in the *htrdr-material*(5) file provided through the
*-M* option. Both, the clouds and the ground, can be infinitely repeated along
the X and Y axis by setting the *-r* and the *-R* options, respectively.
-*htrdr* evaluates the intensity incoming on each pixel of the sensor array. The
-underlying algorithm is based on a Monte-Carlo method: it consists in
-simulating a given number of optical paths originating from the camera,
-directed into the atmosphere, taking into account light absorption and
-scattering phenomena. When rendering in the visible part of the spectrum, the
-computation is performed over the visible part of the spectrum in [380, 780]
+Spectral dimension can be integrated in many ways (*-s* option). By default,
+the computation is performed for the visible part of the spectrum in [380, 780]
nanometers, for the three components of the CIE 1931 XYZ colorimetric space
that are subsequently recombined in order to obtain the final color for each
pixel, and finally the whole image of the scene as seen from the set
-observation position. In longwave, the rendering is performed for the range
-of wavelengths defined by the *-l* option. The estimated radiance per pixel is
-then converted to its brightness temperature and both are saved in the output
-image.
-
-In *htrdr* the spatial unit 1.0 corresponds to one meter, the estimated
-radiance is given in W.sr^-1.m^-2 and the temperatures are expressed in Kelvin.
-The results are written to the output file if the *-o* option is defined and
-the standard output otherwise. The output image is a list of raw ASCII data
-formatted with respect to the *htrdr-image*(5) file format. Since *htrdr*
-relies on the Monte-Carlo method, each estimation is given with its numerical
-accuracy.
+observation position. The two other ways consist in explicitly defining the
+longwave or shortwave spectral range to handle and continuously sampling a
+wavelength in this range according to the Planck function for a reference
+temperature. Actually longwave and shortwave are keywords that mean that the
+source of radiation is whether external or internal to the medium,
+respectively. In shortwave, only the pixel radiance is evaluated and stored in
+the output image. In longwave this estimated radiance is then converted to its
+brightness temperature and both are saved in the image.
+
+In *htrdr* the spatial unit 1.0 corresponds to one meter and the temperatures
+are expressed in Kelvin. The estimated radiances are given in W/sr/m^2 excepted
+for monochromatic computations where the computed spectral radiance is defined
+in W/sr/m^2/nm. The results are written to the output file if the *-o* option
+is defined and the standard output otherwise. The output image is a list of raw
+ASCII data formatted with respect to the *htrdr-image*(5) file format. Since
+*htrdr* relies on the Monte-Carlo method, each estimation is given with its
+numerical accuracy.
During the simulation, *htrdr* dynamically loads/unloads cloud properties to
handle clouds whose data that do not feat in main memory. *htrdr* also supports
@@ -146,10 +153,6 @@ OPTIONS
brightness temperature for the submitted range of wavelengths. By default,
*spp* is set to @HTRDR_ARGS_DEFAULT_IMG_SPP@.
-*-l* __wlen-min__,__wlen-max__::
- Switch in infrared rendering for the longwave interval in [__wlen-min__,
- __wlen-max__] nanometers.
-
*-R*::
Infinitely repeat the _ground_ along the X and Y axis.
@@ -180,6 +183,44 @@ OPTIONS
File where *htrdr* writes its _output_ data. If not defined, write results to
standard output.
+*-s* <__spectral-parameter__:...>::
+ define the type and the range of the spectral integration. Available spectral
+ parameters are:
+
+ **cie_xyz**;;
+ the radiance is computed for the visible part of the spectrum in [380, 780]
+ nanometers with respect to the XYZ CIE 1931 tristimulus values. This is the
+ default comportment of *htrdr*.
+
+ **lw**=**_wlen-min_*,*_wlen-max_*;;
+ perform the spectral sampling continuously in the [_wlen-min_, _wlen-max_]
+ wavelength range (wavelength must be provided in nanometers) according to
+ the Planck function for a reference temperature. If _wlen-min_ and
+ _wlen-max_ are equals the computation is monochromatic. *lw* means for
+ longwave but is here a code word that really means "computation of radiance
+ using the internal source of radiation": in other words, radiation is
+ emitted by the medium and its boundaries. Because the application is mainly
+ for the terrestrial atmosphere, internal radiation is emitted in the
+ thermal longwave part of the electromagnetic spectrum. Therefore the
+ default value of the reference temperature used in the spectral sampling is
+ fixed at 290 K.
+
+ **sw**=**_wlen-min;;
+ perform the spectral sampling continuously in the [_wlen-min_, _wlen-max_]
+ wavelength range (wavelength must be provided in nanometers) according to
+ the Planck function for a reference temperature. If _wlen-min_ and
+ _wlen-max_ are equals the computation is monochromatic. In the present
+ case, *sw* means that the source of radiation is external to the medium:
+ because the application is for the terrestrial atmosphere, the value of the
+ reference temperature is by default fixed at 5778 K, i.e. the blackbody
+ temperature of the Sun.
+
+ **Tref**=**_temperature_**;;
+ reference temperature of the Planck function used to continuously sample the
+ longwave/shortwave spectral range. In longwave, it is set to 290 K by
+ default while in shortwave its default value is the blackbody temperature
+ of the sun (i.e. 5778 K).
+
*-T* _threshold_::
Optical thickness used as threshold criteria to partition the properties of
the clouds. By default its value is @HTRDR_ARGS_DEFAULT_OPTICAL_THICKNESS_THRESHOLD@.
@@ -237,13 +278,14 @@ PPM image [4]:
$ htpp -o image.ppm output
Render the previous scene in infrared for the wavelengths in [9200, 10000]
-nanometers:
+nanometers with a reference temperature of 300 Kelvin:
- $ htrdr -l 9200,10000 -a gas.txt -m Mie.nc -g mountains.obj -R \
+ $ htrdr -a gas.txt -m Mie.nc -g mountains.obj -R \
-M materials.mtl \
-c clouds.htcp \
-C pos=0,0,400:tgt=0,1,0:up=0,0,1 \
-i def=800x600:spp=64 \
+ -s lw=9200,1000:Tref=300
-f -o output
Move the sun by setting its azimuthal and elevation angles to *120* and *40*
