List of changes in isGrafLab (Irregular Surface GRAvity Field LABoratory)
========================================================================
April 2019 (isGrafLab 2.1.2)
Minor updates.
- Fixed an error when running isGrafLab via the batch mode and setting
the variable "Status_bar" to 0 (the computation did not start).
- Added error messages when any of the input files does not exist (GGM file,
DTM file, irregular surface file).
========================================================================
December 2018 (isGrafLab 2.1.1)
Minor updates.
- isGrafLab can now automatically take the maximum degree from the geopotential model and use it
in the synthesis also in the batch mode. This can be achieved by setting the input parameter "nmax"
to the string 'nmaxGGM' (see the description of the input parameters in the source code).
- Fixed an error message that has been introduced in the previous version (typo in the description
of the error; related to the diagonal components of the tensors in LNOF).
- Uploaded new "EGM96.mat" file with the structure that can be read by isGrafLab 2.1.0 and later.
========================================================================
October 2018 (isGrafLab 2.1.0)
Moderate updates focused mostly on improving large-scale computations up to ultra-high
harmonic degrees (well beyond 10800).
- isGrafLab now takes advantage of the equatorial symmetry property of Legendre functions.
This rule provides a mutual relation between Legendre functions for the southern and
the northern hemisphere. It is beneficial in case of large-scale grids that
are symmetric with respect to the equator, necessitating to compute Legendre functions
only for one hemisphere (Legendre functions for the other hemisphere are derived by means
of this rule).
The new version of isGrafLab exploits the symmetry property if *each* of the following
conditions is satisfied:
1) A functional of the geopotential is to be computed (the computation of commission errors
does not exploit the symmetry property).
2) The grid-wise computation mode is selected.
3) The extended-range arithmetic approach is selected to compute Legendre functions
(the whole improvement is tailored to ultra-high harmonic degrees for which the standard
and modified forward column approaches for Legendre functions do not provide accurate results anyway).
4) All positive latitudes have their negative counterpart or vice versa (up to a given threshold to
suppress numerical inaccuracies, currently 100*eps degrees). The zero latitude, i.e., the equator,
may be included in the grid (again, within the 100*eps deg numerical threshold).
If all these conditions are satisfied, the symmetry property is employed *automatically*,
meaning that no additional action from the user is required to enable the more efficient variant.
The gain in the computational speed when synthesising the disturbing potential (setting the maximum order of
the Taylor series to zero) is summarized for a few variants below:
-----------------------------------------------------------------------
Global equiangular | Maximum degree | Improvement of the new
grid (grid size | of the expansion | version in terms of the
as lats x longs) | | computation time
-----------------------------------------------------------------------
30 arcmin (361 x 721) | 360 | 1.3 times faster
5 arcmin (2161 x 4321) | 2160 | 1.5 times faster
1 armin (10801 x 21601) | 10800 | 1.5 times faster
-----------------------------------------------------------------------
Examples of some symmetric grids (shown are only the latitudes):
lat = [-90 -60 -30 0 30 60 90]; %Equator included
lat = [-80 -60 -40 -20 0 20 40 60 80]; %Equator included
lat = [-35 -25 -15 -5 5 15 25 35]; %Equator excluded
lat = [-90 -85 -80 80 85 90];
lat = [-90 -80 -75 -70 -69 -68 -67 -66 -65 65 66 67 68 69 70 75 80 90]; %Varying spacing
Examples of some grids that are not considered as symmetric (shown are only latitudes):
lat = [-90 -60 -30 0 30 60]; %The negative latitude of -90 deg does not have its positive counterpart
lat = [-35 -25 -15 -4.99 5 15 25 35]; %The difference "abs(abs(-4.99)-5)" is larger than the threshold of 100*eps degrees
Note that the four aforementioned conditions imply that the symmetry property can be employed
also when the grid is split into several latitude bands. This is beneficial when the grid is too
large and there is not enough available RAM for isGrafLab (e.g., when isGrafLab is called inside
a parfor loop and the computation is performed on a cluster). The symmetry property can be
exploited even if the latitudes of the individual bands are specified in the following manner: e.g.,
fi = [-90:1:-80 80:1:90];
- isGrafLab is now able to perform the harmonic synthesis even if the minimum degree of the imported
coefficients set is larger than 2. For instance, the input file may contain coefficients only
from the harmonic band 2161,...,10800 or some other.
This is beneficial when the set of spherical harmonic coefficients is too large to fit into
RAM. For instance, coefficients of a degree-43200 expansion require ~30 GB RAM to store them
(the file has 4 columns: degree, order, Cnm, Snm). In such cases, it can be useful
to split the coefficients set into several smaller subsets, such that each subset can be stored
in RAM. For instance, a single coefficients set of a degree-43,200 expansion can be split
into the following harmonic bands: 0,...,2160; 2161,...,4320;...; 38881,...43200. Then, the
computation is performed for each harmonic band separately and the results are summed (if this is permissible
for the particular functional). Note that such computation involves many redundant evaluations of
Legendre functions. Therefore, it is not optimized efficiently, but at least it can be performed.
Example: A file with an incomplete set of spherical harmonic coefficients can be obtained from the
enclosed gravity field model EGM96 (the "EGM96.mat" file) using the following commands:
load('EGM96.mat'); %Loads EGM96, a gravity model up to degree 360
EGM96(EGM96(:,1)<100,:)=[]; %Deletes coefficients below degree 100
save EGM96_nmin100_nmax360.mat -mat -v7.3 EGM96 %Saves the harmonic band 100,...360 of the EGM96 model
The file "EGM96_nmin100_nmax360.mat" can subsequently be imported into isGrafLab.
- The new version of isGrafLab does not require to specify degrees and orders of spherical harmonic
coefficients if sorted as in Table 1 (see below).
Table 1: Structure of the input GGM file - spherical harmonic
coefficients sorted primarily according to degrees.
----------------------------------------
n m Cnm Snm
----------------------------------------
2 0 -0.48417E-03 0.00000E+00
2 1 -0.20662E-09 0.13844E-08
2 2 0.24394E-05 -0.14003E-05
3 0 0.95716E-06 0.00000E+00
----------------------------------------
To employ this functionality, the input file must be in the binary "*.mat" format and must contain
three variables:
1) a matrix of an arbitrary name (following the Matlab's rules) with two columns ([Cnm Snm], cf.
the third and fourth column in Table 1),
2) an integer named as "nmin" specifying the minimum degree of the coefficients to be imported,
3) an integer names as "nmax" specifying the maximum degree of the coefficients to be imported.
Again, this improvement is aimed for a more comfortable handling of ultra-high-degree expansions, for which
the size of the input files containing spherical harmonic coefficients may easily reach a few tens of GB on the disk.
Omitting the first two columns from Table 1 reduces the size of the input file by about one half.
Importantly, the first two columns from Table 1 may be omitted only if the coefficients are sorted
as shown in Table 1. Other orderings of the coefficients, such as the one in Table 2 or others, are
not supported in this case.
Table 2: Structure of the input GGM file - spherical harmonic
coefficients sorted primarily according to orders.
----------------------------------------
n m Cnm Snm
----------------------------------------
2 0 -0.48417E-03 0.00000E+00
3 0 0.95712E-06 0.00000E+00
4 0 0.53998E-06 0.00000E+00
5 0 0.68658E-07 0.00000E+00
----------------------------------------
Note that if the degrees and orders are omitted in the file, isGrafLab does not perform checks of the structure
of the file.
Example: A file with an incomplete set of spherical harmonic coefficients excluding information on degrees and
orders can be obtained from the enclosed gravity field model EGM96 (the "EGM96.mat" file) using
the following commands:
load('EGM96.mat'); %Loads EGM96, a gravity model up to degree 360
%Importantly, the coefficients in this file are stored in agreement with Table 1.
%No reordering of the coefficients is therefore necessary.
EGM96(EGM96(:,1)<100,:)=[]; %Deletes coefficients below degree 100
EGM96(:,1:2)=[]; %Deletes information on degrees and orders
nmin=100; %Specifies the minimum degree of the coefficients
nmax=360; %Specifies the maximum degree of the coefficients
save EGM96_NoDegreesOrders_nmin100_nmax360.mat -mat -v7.3 EGM96 nmin nmax %Saves the harmonic band 100,...360 of the EGM96 model and variables nmin and nmax
The file "EGM96_NoDegreesOrders_nmin100_nmax360.mat" can subsequently be imported into isGrafLab.
- Data computed via the grid-wise mode can now be displayed even without the Mapping Toolbox. This
is possible only when working without the GUI and the variable "Display_data" is set to 2 (cf. the
description of the input variables to the "isGrafLab" function).
The data are plotted simply as a matrix using the "imagesc" function. On the one hand, the plots are not as
pretty as in the case of the Mapping Toolbox, but, on the other hand, the processing time is reduced substantially.
This improvement is therefore suitable for plotting large grids, say, with millions of points.
Example: Using the enclosed EGM96 gravity model, the plots with and without the Mapping Toolbox can be obtained
using the following commands (compute the disturbing potential):
H=zeros(361,721)+3000;
save DEM.mat -mat -v7.3 H
tic
isGrafLab('OK',3986004.415E+8,6378136.3,0,360,1,'EGM96.mat',0,3,-90,0.5,90,0,0.5,360,0,'DEM.mat',0,'Mapping_Toolbox',5,1,[],1,1,0,1,6,1,50,300,1)
toc
tic
isGrafLab('OK',3986004.415E+8,6378136.3,0,360,1,'EGM96.mat',0,3,-90,0.5,90,0,0.5,360,0,'DEM.mat',0,'No_Mapping_Toolbox',5,1,[],1,1,0,2,6,1,50,300,1)
toc
Here, the case when Mapping Toolbox is not used is 13 times faster (the time that is needed for the synthesis is negligible here).
Even more impressive improvement is obtained when the grid is larger and/or a functional that strongly varies is to be displayed. For instance, the "imagesc"
function (that is, not using Mapping Toolbox) is 450 times faster when the gravity disturbances are computed using the previous example:
H=zeros(361,721)+3000;
save DEM.mat -mat -v7.3 H
tic
isGrafLab('OK',3986004.415E+8,6378136.3,0,360,1,'EGM96.mat',0,3,-90,0.5,90,0,0.5,360,0,'DEM.mat',0,'Mapping_Toolbox',21,1,[],1,1,0,1,6,1,50,300,1)
toc
tic
isGrafLab('OK',3986004.415E+8,6378136.3,0,360,1,'EGM96.mat',0,3,-90,0.5,90,0,0.5,360,0,'DEM.mat',0,'No_Mapping_Toolbox',21,1,[],1,1,0,2,6,1,50,300,1)
toc
- The numerical outputs from isGrafLab can now be taken directly as the output from the function "isGrafLab".
The structure of the output variable is the same as in case of the output files.
Example: A test computation (look for the text "TEST RUN" in the source code of isGrafLab) can be run as follows (generates
the data "txt" file, report file and returns the computed data in the Matlab environment through the variable "output"):
output=isGrafLab('OK',3986004.415E+8,6378136.3,0,360,1,'EGM96.mat',0,1,[],[],[],[],[],[],[],'input.txt',[],[],[],'my_output',0,5,1,[],1,1,0,[],[],[],[],[],1);
- Improved reading of the "gfc" files header.
========================================================================
June 2018 (isGrafLab 2.0.2)
Minor update.
- Fixed bug when loading an irregular surface file that is i) in the binary
"mat" format, and ii) stored in a different directory than the source code
"isGrafLab.m". The older version thrown error and did not start the computation.
========================================================================
September 2017 (isGrafLab 2.0.1)
Minor updates.
- Improved reading of the "gfc" files header.
The earlier versions of isGrafLab were not able to read "gfc" format for some models,
such as GECO, that contain in the header of the files physical units after the values of
"earth_gravity_constant" and "radius".
isGrafLab now also checks the normalization of the spherical harmonic coefficients (only
the "fully_normalized" option is supported).
- If the irregular surface file is given in the MAT format, isGrafLab now checks
dimensions of the grid prior to the computation.
- An additional error check added when computing "Geoid_undulation" or "Height_anomaly".
isGrafLab now verifies whether the maximum degree of the DTM is sufficiently large compared
with the maximum degree used to compute the two functionals from a geopotential model.
- Minor improvements in displaying the status bar when working without the GUI.
=======================================================================
January 2017 (isGrafLab 2.0)
This is a major update of isGrafLab.
- isGrafLab can now be fully controlled without the GUI.
The test computation (see the file "user_manual_isGrafLab.txt", section "Test
computation") can be run using the following command:
isGrafLab('OK',3986004.415E+8,6378136.3,0,360,1,'EGM96.mat',0,3,48,1,49,20,1,22,0,'input.txt',0,'my_output',5,1,[],1,1,0,[],[],[],[],[],1)
The description of the input variables can be found in the source code (look for the text:
"function isGrafLab")
- The functional "Gravity" has been replaced by a new one, which is named "Gravity_vector_gX_gY_gZ".
The functional "Gravity_vector_gX_gY_gZ" yields three elements of the gravity vector in the LNOF,
while the original functional "Gravity" was defined as the magnitude of the gravity vector.
"Gravity" can easily be computed from "Gravity_vector_gX_gY_gZ" via sqrt(gX^2+gY^2+gZ^2).
For the definition of this functional, see
"Definition_of_functionals_of_the_geopotential_used_in_GrafLab_software.pdf".
- When working without the GUI, a custom reference ellipsoid can now be defined by 5 parameters:
geocentric gravitational constant, semimajor axis, the first numerical eccentricity,
the 4*pi fully normalized spherical harmonic coefficient C20 and the angular velocity.
This option is not available via the GUI.
- Computations can now be performed on user-specified grids defined by vectors
of latitudes and longitudes. Within each of the two vectors, varying spacing is supported.
- Functions to transform ellipsoidal/spherical coordinates into cartesian ones and vice versa
have been replaced by own functions in order to remove the dependency of the computation part
of the code on the Mapping Toolbox. To display data on a map, Mapping Toolbox is still required.
The new functions can be found at the end of the source code.
Original function <--> New function
geodetic2ecef <--> ell2cart
ecef2geodetic <--> cart2ell
sph2cart <--> sph2cart (the same name, but the new function is used)
cart2sph <--> cart2sph (the same name, but the new function is used)
The input and output parameters of the matching functions remain the same.
- The version 7.3 of the Matlab's binary file format is now used by default to save the computed
data into a MAT-file. This version allows to save data greater than 2 GB on 64-bit systems.
- Minor modifications of the report file.
- Some error checks are added or slightly modified.
Some useful tips and tricks:
- Example No. 1:
To compute gravitational vector in the LNOF (i.e. the gravity vector without the centrifugal part),
choose the functional "Gravity_vector_gX_gY_gZ" and use a custom reference ellipsoid with the angular
velocity being equal to zero:
isGrafLab('OK',3986004.415E+8,6378136.3,0,360,[3986005*10^8 6378137 sqrt(0.006694380022903416) -108263*10^-8/sqrt(5) 0],'EGM96.mat',0,3,48,1,49,20,1,22,0,'input.txt',0,'Example_1',16,1,[],1,1,0,[],[],[],[],[],1)
Here, the GRS80 reference ellipsoid is used (look for "%GRS80" in the source code to obtain
the 5 defining parameters) with the angular velocity set to zero. Note that even though the functional
"Gravity_vector_gX_gY_gZ" is independent of the reference ellipsoid and of its normal gravity field, it
has to be defined for two reasons: 1) in all computations, isGrafLab takes the value of the angular velocity
from the defining parameters of the reference ellipsoid, since global gravity field models usually do not
specify this parameter; 2) isGrafLab needs the values of the semimajor axis and of the first numerical
eccentricity if the input coordinates are ellipsoidal (which is the case of the aforementioned example).
The ellipsoidal coordinates have to be to transformed into spherical ones, which are then used to perform
spherical harmonic synthesis; hence the values of the semimajor axis and of the first numerical eccentricity
are required for the transformation step. In the case of computational points defined by spherical coordinates,
all 5 defining parameters can be set to zero, as they are not used in the computation.
Note, however, that in the report file, the name of the functional "Gravity_vector_gX_gY_gZ" will appear,
not "Gravitational_vector_gX_gY_gZ".
- Example No. 2:
If you wish to compute some functional that originally employs the normal gravity field of a reference ellipsoid
(e.g. the gravity disturbance in spherical approximation -- "Gravity_disturbance_sa"), but without the normal
gravity field, set the parameters GM, C20 and omega to zero:
isGrafLab('OK',3986004.415E+8,6378136.3,0,360,[0 6378137 sqrt(0.006694380022903416) 0 0],'EGM96.mat',0,3,48,1,49,20,1,22,0,'input.txt',0,'Example_2',21,1,[],1,1,0,[],[],[],[],[],1)
In this case, we obtained the negative first-order radial derivative of the gravitational potential. Again,
the values of the semimajor axis and of the first eccentricity of the reference ellipsoid are required, as
the computation points are defined by ellipsoidal coordinates and have to be transformed into spherical ones.
Note that in the report file, the name of the functional "Gravity_disturbance_sa" will appear.
- Example No. 3:
isGrafLab now allows to perform a fast spherical harmonic synthesis on grids defined by varying spacing in the latitudinal
and/or the longitudinal directions.
This option can be used, e.g., to perform synthesis on a grid defined in ellipsoidal coordinates, but with equal spacing of the
latitudes in terms of spherical coordinates. Suppose that we wish to compute some functional on a grid at irregular surface
with equal spacing in spherical latitude (i.e., the spacing in terms of ellipsoidal latitudes varies). The grid, at the surface
from which the functional is continued, is defined by the spherical latitudes "phi_sph=48:1:49", the longitudes "lambda=20:1:22" and
the height of the grid above the reference ellipsoid "h=0". The spherical latitudes "phi_sph" can be transformed into ellipsoidal
ones "phi_ell", and these ellipsoidal latitudes (with varying spacing) can now be used as the input ellipsoidal coordinates.
Example commands:
phi_sph=[48:1:49]'; %Vector of spherical latitudes
lambda=[20:1:22]'; %Vector of longitudes
eEl=sqrt(0.006694380022903416); %The first eccentricity of GRS80
phi_ell=atan(tan(phi_sph*pi/180)./sqrt(1-eEl^2))*180/pi; %Transformation of spherical latitudes into ellipsoidal latitudes (this formula holds only for points lying on the reference ellipsoid)
isGrafLab('OK',3986004.415E+8,6378136.3,0,360,1,'EGM96.mat',0,3,phi_ell,'empty','empty',lambda,'empty','empty',0,'input.txt',0,'Example_3',5,1,[],1,1,0,[],[],[],[],[],1)
These commands compute the disturbing potential from EGM96 up to degree and order 360. The grid, from which the functional is
continued, is equiangular in spherical coordinates (the step in the both the latitudinal and the longitudinal direction is 1°),
but is non-equiangular in terms of ellipsoidal latitudes, as the spacing in ellipsoidal latitudes varies.
========================================================================
April 2016 (isGrafLab 1.1.2)
- Minor modifications to ensure compatibility with the latest releases of
Matlab.
========================================================================
August 2015 (isGrafLab 1.1.1)
- Accelerated routine to compute the fully normalized associated Legendre functions
via the extended-range arithmetic approach on 64-bit Matlab. For example,
for "nmax=2190" and 1801 latitudes, the new routine is approximately two times
faster then the previous one. The routine for 32-bit Matlab remains the same.
========================================================================
April 2014 (isGrafLab 1.1)
- The earlier version of isGrafLab automatically assumed that the spherical
harmonic coefficients of the degrees 0 and 1 are set as follows: C00=1, C10=0,
C11=0 and S11=0. There is no such a restriction in the new version 1.1.
This means that, for example, spherical harmonic coefficients of the
potential of topographic masses can now be imported and used with nmin = 0
(instead of nmin = 2 as in the previous versions of isGrafLab). In general,
in the case of the potential of topographic masses, these coefficietns have
different values from the ones stated above.
Thereby, the following functionals must be computed with nmin = 0: "Geoid
undulation", "Height anomaly", "Gravity disturbance", and the non-diagonal
elements of the disturbing and the gravitational tensor in the LNOF. The rest
of the functionals can be computed with a value of nmin in the interval
0 <= nmin <= nmax. For a detailed overview, please, see Table 3 in the source
code "isGrafLab.m".
If the input GGM file does not specify any of these coefficients, isGrafLab will
automatically use the aforementioned values.
- isGrafLab 1.1 computes the zonal spherical harmonic coefficients of the reference
ellipsoid up to degree n = 20 (in the previous version this value was set to
n = 10 which is sufficient in the vast majority of practical applications).
The differences compared to n = 10 are of very small orders of magnitude,
although might be noticeable in the results provided by isGrafLab. For example,
the differences in terms of the disturbing potential are approximately of the
order of 10^-8 m^2*s^-2 or so.
=======================================================================
May 2014 (isGrafLab 1.00, a modified version of GrafLab 1.1.2)
- Published in Computers & Geosciences 66 (2014), pp. 219-227,
doi: 10.1016/j.cageo.2014.02.005.