This program creates a PVL template file to be used in
photometry-based applications, such as photomet. Each planet
has different surface and atmospheric properties requiring different
model specifications. It is important to set up the models with unique
parameter values that apply to a specific planetary body. There are
two types of correction models that can be specified in this program:
Photometric - describes the planetary surface of an image
Atmospheric - applies to the atmosphere through which an image was acquired
The normalization models are not specified in this program, but only three
models (albedoatm, shadeatm, and topoatm) apply atmosperheric correction.
Choose an atmospheric model only if one of the three normalization models
listed above will be applied with the photomet program.
This program allows the use of a PVL file that contains preset parameter names for
different photometric and atmospheric models. NOTE: if the user leaves the
ZEROB0STANDARD parameter set to READFROMPVL and does not provide an input PVL
file, then the ZEROB0STANDARD parameter will default to TRUE.
Within the GUI, the user may select a PVL file and then use the drop-down
menu to view the contents of the PVL file or to load the parameter values
from the PVL file into the appropriate parameter names in the GUI. Note:
If more than one model for "PhtName" or "AtmName" are in the PVL file,
then the parameter values for the first model type encountered by the program
will be loaded into the GUI. Review the parameter names and values to make
sure the correct options and values are displayed before executing the program.
Below are examples of parameter settings within a PVL file:
PVL file examples:
Example 1: Example 2:
Object = PhotometricModel Object = PhotometricModel
Group = Algorithm Group = Algorithm
PhtName = Lambert PhtName = Minnaert
EndGroup K = 0.5
EndObject EndGroup
EndObject
Example 3: Example 4:
Object = PhotometricModel Object = PhotometricModel
Group = Algorithm Group = Algorithm
PhtName = Hapkehen PhtName = Lunarlambertmcewen
Wh = 0.52 EndGroup
Hh = 0.0 EndObject
B0 = 0.0
Theta = 30.0
Hg1 = 0.213
Hg2 = 1.0
EndGroup
EndObject
Object = AtmosphericModel
Group = Algorithm
AtmName = Hapkeatm2
Hnorm = 0.003
Tau = 0.28
Tauref = 0.0
Wha = 0.95
Hga = 0.68
EndGroup
EndObject
Example 5:
Object = PhotometricModel
# For Mars red filter images
# The phase angles at which the coefficient values for the Lunar Lambert
# Empirical L and the Minnaert Empirical K approximation are
# calculated, along with the brightness (phase curve) values at those
# points (ALL ON ONE LINE!)
Group = Algorithm
PhtName = LunarLambertEmpirical
PhaseList = "0.,10.,20.,30.,40.,50.,60.,70.,80.,90.,100.,110.,120.,130.,
140.,150.,160.,170.,180."
LList = "0.946,0.748,0.616,0.522,0.435,0.350,0.266,0.187,0.118,0.062,0.018,
-0.012,-0.027,-0.035,-0.036,-0.037,-0.031,-0.012,-0.010"
PhaseCurveList = "0.1578,0.1593,0.1558,0.1484,0.1391,0.1292,0.1194,0.1099,
0.1008,0.09176,0.08242,0.07234,0.06165,0.05106,0.04091,
0.03137,0.02171,0.01038,0."
EndGroup
Group = Algorithm
PhtName = MinnaertEmpirical
# The numbers below are entered on a single line in the text file for each
# parameter name (see $ISISROOT/appdata/templates/photometry/marsred.pvl).
PhaseList = "0.,10.,20.,30.,40.,50.,60.,70.,80.,90.,100.,110.,120.,130.,
140.,150.,160.,170.,180."
KList = "0.518,0.595,0.660,0.709,0.753,0.796,0.837,0.875,0.904,0.922,
0.926,0.935,0.954,0.986,1.019,1.063,1.099,1.095,1.090"
PhaseCurveList = "0.1574,0.1582,0.1546,0.1470,0.1375,0.1273,0.1174,0.1077,
0.09797,0.08750,0.07594,0.06466,0.05471,0.04665,0.03935,
0.03339,0.02642,0.01482,0."
EndGroup
EndObject
Below are equations for some of the photometric model functions,
where phase is the phase angle, and u0 and u are the cosines of the
incidence angle and emission angle, respectively:
SURFACE PHOTOMETRIC FUNCTION
Available photometric models and equations
Photometric Model Name
Function Equation
Lambert
u0
LommelSeeliger
u0/(u0+u)
Minnaert
u0**K * u**(K-1)
LunarLambert ("lunar" part is Lommel-Seeliger)
(1-L)*u0 + 2*L*u0/(u0+u)
MinnaertEmpirical
B(phase) * u0**K(phase) * u**(K(phase)-1)
LunarLambertEmpirical
B(phase) * ((1-L)*u0 + 2*L*u0/(u0+u))
Hapkehen (Hapke-Henyey-Greenstein)
No equation available
Hapkeleg (Hapke-Legendre)
No equation available
LunarLambertMcEwen
No equation available
References:
Chandrasekhar, S., 1960. Radiative Transfer. Dover, 393 pp.
Hapke, B. W., 1981. Bidirectional reflectance spectroscopy 1: Theory. J.
Geophys. Res., pp. 86,3039-3054.
Hapke, B., 1984. Bidirectional reflectance spectroscopy3: Corrections for
macroscopic roughness. Icarus, 59, pp. 41-59.
Hapke, B., 1986. Bidirectional reflectance spectroscopy 4: The extinction
coefficient and the opposition effect. Icarus, 67, pp. 264-280.
Kirk, R. L., Thompson, K. T., Becker, T. L., and Lee, E. M., 2000.
Photometric modelling for planetary cartography. Lunar Planet. Sci., XXXI,
Abstract #2025, Lunar and Planetary Institute, Houston (CD-ROM).
See photomet documetation for additional information.
Use this parameter to select an existing PVL filename that contains a
description of the photometric properties of a planetary body. The
information in this file will be merged with the information that is
input through the user interface or command line to create the output
PVL file.
Type
filename
File Mode
input
Default Path
$ISISROOT/appdata/templates/photometry
Internal Default
None Specified
Filter
*.pvl
Files:
TOPVL
Description
Use this parameter to select or enter the output filename. If the
file already exists it will be overwritten. The ".pvl" extension is
automatically appended to the filename if no extension is entered.
Type
filename
File Mode
output
Filter
*.pvl
Photometric Parameters:
PHTNAME
Description
This is the name of the surface photometric function model to use
to apply the photometric correction. Both the abbreviated names
and the full model names are valid entries.
Type
combo
Default
FROMPVL
Internal Default
FROMPVL
Option List:
Option
Brief
Description
FROMPVL
Get photometric model from PVL file
Get the photometric model from the PVL file. Add any missing
parameters to the PVL file, or enter the values on the command
line or use the GUI to enter the values.
Exclusions
THETA
WH
HG1
HG2
HH
B0
BH
CH
L
K
PHASELIST
KLIST
LLIST
PHASECURVELIST
ZEROB0STANDARD
HAPKEHEN
Hapke-Henyey-Greenstein photometric model
Derive model albedo using complete Hapke model with Henyey-Greenstein
single-particle phase function whose coefficients are hg1 and hg2,
plus single scattering albedo wh, opposition surge parameters hh
and b0, and macroscopic roughness theta. For a smooth model with opposition
effect use theta=0.
Exclusions
BH
CH
L
K
PHASELIST
KLIST
LLIST
PHASECURVELIST
Inclusions
THETA
WH
HG1
HG2
HH
B0
HAPKELEG
Hapke-Legendre photometric model
Derive model albedo using complete Hapke model with Henyey Legendre
two-term Legendre polynomial phase function whose coefficients are bh
and ch, plus single scattering albedo wh, opposition surge parameters
hh and b0, and macroscopic roughness theta.
Exclusions
HG1
HG2
L
K
PHASELIST
KLIST
LLIST
PHASECURVELIST
Inclusions
THETA
WH
BH
CH
HH
B0
LAMBERT
Lambert photometric model
Simple photometric model which predicts that light incident on
a surface is scattered uniformly in all directions; the total
amount of reflected light depends on the incidence angle
of the illumination. This function does not depend upon the
outgoing light direction.
Exclusions
THETA
WH
HG1
HG2
HH
B0
BH
CH
L
K
PHASELIST
KLIST
LLIST
PHASECURVELIST
LOMMELSEELIGER
Lommel-Seeliger photometric model
This model takes into account the radiance that results from
single scattering (scattering of collimated incident light) and
does not take into account the radiance that results from multiple
scattering (scattering of diffuse light which has made its way
indirectly to the same position by being scattered one or more
times). This model depends on the incidence and emission angles.
Exclusions
THETA
WH
HG1
HG2
BH
CH
HH
B0
L
K
PHASELIST
KLIST
LLIST
PHASECURVELIST
LUNARLAMBERT
Lunar Lambert photometric model
This model combines a weighted sum of the LommelSeeliger and
Lambert models. Given a suitable value for the LunarLambert
function weight, L, this model fits the true reflectance behavior
of many planetary surfaces equally well as the Hapke model. This
model also depends on the incidence and emission angles.
Exclusions
THETA
WH
HG1
HG2
BH
CH
HH
B0
K
PHASELIST
KLIST
LLIST
PHASECURVELIST
Inclusions
L
LUNARLAMBERTEMPIRICAL
Lunar Lambert Empirical photometric model
This model combines a weighted sum of the LommelSeeliger and
Lambert models. Given a suitable value for the LunarLambert
function weight, L, this model fits the true reflectance behavior
of many planetary surfaces equally well as the Hapke model.
This model also depends on the incidence and emission angles.
Exclusions
THETA
WH
HG1
HG2
BH
CH
HH
B0
K
L
KLIST
Inclusions
PHASELIST
LLIST
PHASECURVELIST
LUNARLAMBERTMCEWEN
Lunar Lambert-McEwen photometric model
This model was developed specifically for use with the Moon to be
used in conjunction with the MoonAlbedo normalization model.
Exclusions
THETA
WH
HG1
HG2
BH
CH
HH
B0
L
K
PHASELIST
KLIST
LLIST
PHASECURVELIST
MINNAERT
Minnaert photometric model
This model combines a weighted sum of the LommelSeeliger and
Lambert models. Given a suitable value for the LunarLambert
function weight, L, this model fits the true reflectance behavior
of many planetary surfaces equally well as the Hapke model. This
model also depends on the incidence and emission angles.
Exclusions
THETA
WH
HG1
HG2
BH
CH
HH
B0
L
PHASELIST
KLIST
LLIST
PHASECURVELIST
Inclusions
K
MINNAERTEMPIRICAL
Minnaert Empirical photometric model
This model combines a weighted sum of the LommelSeeliger and
Lambert models. Given a suitable value for the LunarLambert
function weight, L, this model fits the true reflectance behavior
of many planetary surfaces equally well as the Hapke model. This
model also depends on the incidence and emission angles.
Exclusions
THETA
WH
HG1
HG2
BH
CH
HH
B0
K
L
LLIST
Inclusions
PHASELIST
KLIST
PHASECURVELIST
Photometric Parameters:
THETA
Description
The "macroscopic roughness" of the surface as it affects
the photometric behavior, used for Hapkehen or Hapkeleg.
This is the RMS slope at scales larger than
the distance photons penetrate the surface but smaller than a pixel.
The roughness correction, which will be evaluated if theta is given
any value other than 0.0, but is extremely slow. See Hapke (1986).
Type
string
Default
None Specified
Internal Default
None Specified
Minimum
0.0
(inclusive)
Maximum
90.0
(inclusive)
Photometric Parameters:
WH
Description
The Hapke single scattering albedo of surface particles,
see Hapke (1981).
Type
string
Default
None Specified
Internal Default
None Specified
Minimum
0.0
(exclusive)
Maximum
1.0
(inclusive)
Photometric Parameters:
HG1
Description
Asymmetry parameter used in Hapke Henyey Greenstein model
for the scattering phase function of single particles in the
surface. See Hapke (1981). The two-parameter Henyey Greenstein
function is:
The Hapke Henyey Greenstein coefficient for single particle phase
function. Second parameter of the two-parameter Henyey-Greenstein
model for the scattering phase function of single particles in the
surface. This parameter controls the proportions in a linear
mixture of ordinary Heneyey Greenstein phase functions with asymmetry
parameters equal to +hg1 and -hg1. See HG1 for the full formula.
Type
string
Default
None Specified
Internal Default
None Specified
Minimum
0.0
(inclusive)
Maximum
1.0
(inclusive)
Photometric Parameters:
BH
Description
The Hapke Legendre coefficient for single particle phase
function. A two-term Legendre polynomial is used for the scattering
phase function of single particles in the surface:
Bh is not to be confused with the legendre coefficient bha
of the phase function for atmospheric particles, used when
atmname=anisotropic1 or anisotropic2.
Type
string
Default
None Specified
Internal Default
None Specified
Minimum
-1.0
(exclusive)
Maximum
1.0
(exclusive)
Photometric Parameters:
CH
Description
The Hapke Legendre coefficient for single particle phase
function. A two-term Legendre polynomial is used for the scattering
phase function of single particles in the surface:
The Hapke opposition surge component. The width parameter for the
opposition effect for the surface if Hapkehen or Hapkeleg is used.
See Hapke (1984).
Type
string
Default
None Specified
Internal Default
None Specified
Minimum
0.0
(inclusive)
Photometric Parameters:
B0
Description
The Hapke opposition surge component. The magnitude of the opposition
effect for the surface if Hapkehen or Hapkeleg is used. See Hapke (1984).
Type
string
Default
None Specified
Internal Default
None Specified
Minimum
0.0
(inclusive)
Photometric Parameters:
ZEROB0STANDARD
Description
This specifies if the opposition surge component B0 is set to zero
during the standard conditions phase. NOTE: The program will automatically
default to "TRUE" if "ZEROBSTANDARD" is not defined by the user.
Type
string
Default
TRUE
Option List:
Option
Brief
Description
READFROMPVL
Get ZEROB0STANDARD value from the FROMPVL file
Retrieve and set the ZEROB0STANDARD parameter from the FROMPVL file. If
a FROMPVL file is not provided, then an error will occur. NOTE: If the
user does not define a value for ZEROB0STANDARD in the input PVL file,
then the ZEROB0STANDARD value will default to TRUE.
FALSE
B0 will not be set to zero for standard conditions phase
This option specifies that the opposition surge B0 will not be set to zero
during the standard conditions phase.
TRUE
B0 will be set to zero for standard conditions phase
This option specifies that the opposition surge B0 will be set to zero
during the standard conditions phase.
Photometric Parameters:
L
Description
The Lunar Lambert function weight that governs limb-darkening
in the lunar lambert photometric function:
Func=(1-L)*u0 + 2*L*u0/(u0+u)
The values generally fall in the range from 0 (Lambert function) to 1
(Lommel-Seeliger or "lunar" function).
Type
string
Default
None Specified
Internal Default
None Specified
Photometric Parameters:
K
Description
The Minnaert function exponent that governs limb-darkening in the
Minnaert photometric function:
Func = u0**K * u**(K-1)
The values generally fall in the range from 0.5 ("lunar-like",
almost no limb darkening) to 1.0 (Lambert function).
Type
string
Default
None Specified
Internal Default
None Specified
Minimum
0.0
(inclusive)
Photometric Parameters:
PHASELIST
Description
The Minnaert Empirical and Lunar Lambert Empirical function phase
angle list entered as a comma delimited string describing how the
parameters of the empirical function vary with phase angle.
See "$ISISROOT/appdata/templates/photometry/marsred.pvl" for an example.
Type
string
Default
No List
Internal Default
No List
Photometric Parameters:
KLIST
Description
The Minnaert Empirical function exponent list of limb darkening values
entered as a comma delimited string that describes how the parameters
of the empirical function vary with phase angle.
See "$ISISROOT/appdata/templates/photometry/marsred.pvl" for an example.
Type
string
Default
No List
Internal Default
No List
Photometric Parameters:
LLIST
Description
The Lunar Lambert Empirical function parameter list of limb darkening
values entered as a comma delimited string that describes how the
parameters of the empirical function vary with phase angle. See
"$ISISROOT/appdata/templates/photometry/marsred.pvl" for an example.
Type
string
Default
No List
Internal Default
No List
Photometric Parameters:
PHASECURVELIST
Description
The Minnaert Empirical or Lunar Lambert Empirical function phase curve
list of brightness values corresponding to a set of phase angles
defined in the PHASELIST parameter. See
"$ISISROOT/appdata/templates/photometry/marsred.pvl" for an example.
Type
string
Default
No List
Internal Default
No List
Atmospheric Parameters:
ATMNAME
Description
This is the name of the atmospheric photometric function model to be
applied. The models ending with "1" use a first order scattering
approximation. Those ending with "2" use a second order scattering
approximation, and are slower but more accurate than the first order
scattering approximation. The atmospheric correction can be used with
only three atmospheric normalization models: albedoatm, shadeatm,
and topoatm. See Kirk et al. (2001).
Type
combo
Default
NONE
Internal Default
NONE
Option List:
Option
Brief
Description
NONE
No atmospheric model
No atmospheric correction will be applied.
Exclusions
HNORM
BHA
TAU
TAUREF
WHA
HGA
NULNEG
ANISOTROPIC1
Anisotropic 1 atmospheric model
Uses Chandrasekhar's solution for anisotropic scattering described
by a one term Legendre polynomial. This model uses first order
scattering approximation.
Exclusions
HGA
Inclusions
HNORM
BHA
TAU
TAUREF
WHA
ANISOTROPIC2
Anisotropic 2 atmospheric model
Uses Chandrasekhar's solution for anisotropic scattering described
by a one term Legendre polynomial. This model uses second order
scattering approximation. It is slower but more accurate than
Anisotropic1.
Exclusions
HGA
Inclusions
HNORM
BHA
TAU
TAUREF
WHA
HAPKEATM1
Hapke 1 atmospheric model
Provides an approximation for strongly anisotropic scattering that
is similar to Hapke's model for a planetary surface. The
Chandrasekhar solution for isotropic scattering is used for the
multiple scattering terms, and a correction is made to the singly
scattered light for anisotropic particle phase function. A one-term
Henyey Greenstein function is used. This model uses a first
order scattering approximation.
Exclusions
BHA
Inclusions
HNORM
HGA
TAU
TAUREF
WHA
HAPKEATM2
Hapke 2 atmospheric model
Provides an approximation for strongly anisotropic scattering that
is similar to Hapke's model for a planetary surface. The
Chandrasekhar solution for isotropic scattering is used for the
multiple scattering terms, and a correction is made to the singly
scattered light for anisotropic particle phase function. A
one-term Henyey Greenstein function is used. This model uses a
second order scattering approximation. It is slower but more
accurate than HAPKEATM1.
Exclusions
BHA
Inclusions
HNORM
HGA
TAU
TAUREF
WHA
ISOTROPIC1
Isotropic 1 atmospheric model
Uses Chandrasekhar's solution for isotropic scattering. This
model uses first order scattering approximation.
Exclusions
HGA
BHA
Inclusions
HNORM
TAU
TAUREF
WHA
ISOTROPIC2
Isotropic 2 atmospheric model
Uses Chandrasekhar's solution for isotropic scattering. This model
uses second order scattering approximation. It is slower but more
accurate than Isotropic1.
Exclusions
HGA
BHA
Inclusions
HNORM
TAU
TAUREF
WHA
Atmospheric Parameters:
NULNEG
Description
This specifies if negative values after removal of atmospheric
effects will be set to NULL. Negative values are only generated
in modes that include atmospheric correction and occur when the
optical depth "tau" is overestimated, so that the atmospheric
radiance subtracted from the image is brighter than the
darkest observed pixels. In this case "tau" should be decreased
until no negative values are present in the output file.
Type
string
Default
READFROMPVL
Option List:
Option
Brief
Description
READFROMPVL
Get NULNEG value from the FROMPVL file
Retrieve and set the NULNEG parameter from the FROMPVL file.
An error is reported if a PVL file is not provided.
NO
Do not set negative values to NULL
This option specifies not to set negative values to NULL after
the removal of atmospheric effects.
YES
Negative values will be set to NULL
This option specifies to set negative values to
NULL after the removal of atmospheric effects.
Atmospheric Parameters:
TAU
Description
The normal optical depth of the atmosphere.
Type
string
Default
None Specified
Internal Default
None Specified
Minimum
0.0
(inclusive)
Atmospheric Parameters:
TAUREF
Description
The reference value of tau to which the image will be normalized. This
would normally be 0.0 unless one is interested in simulating a hazy
atmosphere scene.
Type
string
Default
None Specified
Internal Default
None Specified
Minimum
0.0
(inclusive)
Atmospheric Parameters:
HGA
Description
The coefficient of single particle Henyey Greenstein phase
function. Henyey-Greenestein asymmetry parameter for atmospheric
particle phase function, used in hapkeatm1 and hapkeatm2 atmospheric models.
Not to be confused with corresponding parameter hg1 for the
surface particles.
Type
string
Default
None Specified
Internal Default
None Specified
Minimum
-1.0
(exclusive)
Maximum
1.0
(exclusive)
Atmospheric Parameters:
WHA
Description
The single scattering albedo of atmospheric particles.
Type
string
Default
None Specified
Internal Default
None Specified
Minimum
0.0
(exclusive)
Maximum
1.0
(inclusive)
Atmospheric Parameters:
BHA
Description
The coefficient of the single particle Legendre phase function.
Coefficient of P1 (cosine) term of atmospheric particle phase
function, used in anisotropic1 and anisotropic2 atmospheric models.
Not to be confused with corresponding coefficient bh for the
surface particles.
Type
string
Default
None Specified
Internal Default
None Specified
Minimum
-1.0
(inclusive)
Maximum
1.0
(inclusive)
Atmospheric Parameters:
HNORM
Description
The atmospheric shell thickness normalized to the planet
radius, used to modify angles to get more accurate path lengths
near the terminator (Ratio of scale height to the planetary
radius). The hnorm parameter is defined as "0.003" for Mars,
which is the only planet for which the atmospheric modes are
currently used.
Type
string
Default
None Specified
Internal Default
None Specified
Minimum
0.0
(inclusive)
Examples
Example 1
Create a PVL file of photometric parameters
Description
This example shows the GUI and the parameter name settings. The helper option
is used to load the preset parameter values if an existing PVL file is used,
and then the required parameter names without any values are manually added.
Command Line
photemplate
Run photemplate to generate a PVL file with the parameter values for the
selected photometric models.
GUI Screenshot
photemplate GUI
photemplate GUI
Screenshot of GUI version of the application. The parameter values
have been loaded and edited for the output PVL file.
The output PVL file will contain the photometric parameters to be applied
to the input cube. Load the PVL file parameters using the photemplate GUI
and manually enter required parameter names without any values assigned.
History
Noah Hilt
2008-11-18
Original version.
Janet Barrett
2011-09-23
1) The entire user interface has been redesigned. The previous version of this
program made use of radio button lists to allow the user to choose a photometric
model or an atmospheric model. In order to make the program more compact, the
radio button lists were replaced with drop down menus. When an option is chosen
from the drop down menu, the parameters that apply to that option are made visible.
Parameters that don't apply to that option remain hidden. This helps to make the
interface look less cluttered than it did when every parameter and every option
were visible all the time.
2) The "NORMALIZATION" option is no longer available in this program. This program's
main use is to create files with preset photometric and atmospheric values for use
with various planets. The normalization models are not specific to individual
planets like the atmospheric and photometric models are. The normalization mode
is only used in the photomet program, so this information now needs to be
provided through photomet.
3) The PVL parameter was replaced with the TOPVL parameter. The PHOTOMETRIC
parameter was replaced with PHTNAME. The ATMOSPHERIC parameter was replaced with
ATMNAME.
4) The BHAREF, HGAREF, and WHAREF parameters were removed because they have
become obsolete.
5) The Hapke Legendre (HAPKELEG), empirical Minnaert (MINNAERTEMPIRICAL), and
empirical Lunar Lambert (LUNARLAMBERTEMPIRICAL) photometric functions have
been added.
6) Documentation describing the parameters is still central to the photomet
program. The documentation will be moved into this program in the next ISIS
release.
7) Helper buttons were added to the FROMPVL to allow you to View a PVL or to Load
a PVL. PLEASE NOTE: When loading a Minnaert Empirical or Lunar Lambert Empirical
model from a PVL, only the first value will be loaded into the GUI. This is
a known problem and will be fixed in the next patch or release to ISIS.
8) ***NOTE*** The Minnaert Empirical and Lunar Lambert Empirical models do not
load properly from a PVL file when using the Load Pvl helper button. This is
a known problem and will be fixed in the next patch or release of ISIS.
Sharmila Prasad
2011-10-27
Added API's to display and output PVL information, specifically for arrays and
alphabetically organized the Photometric Model names.
Ella Mae Lee
2012-11-16
Improved the documentation, fixes #452.
Lynn Weller
2013-02-25
Removed links to applications imbedded in text and replaced with
italicized application name. Added application links to the
"Related Objects and Documents" section of the documentation.
Fixes mantis ticket #1525.