Ubuntu Manpage: GeoidEval -- look up geoid heights

Provided by: geographiclib-tools_1.21-1ubuntu1_amd64

NAME

       GeoidEval -- look up geoid heights

SYNOPSIS

       GeoidEval [ -n name ] [ -d dir ] [ -l ] [ -a | -c south west north east ] [ -g ] [ -z zone
       ] [ --msltohae ] [ --haetomsl ] [ -v ] [ --comment-delimiter commentdelim ] [ --version |
       -h | --help ] [ --input-file infile | --input-string instring ] [ --line-separator linesep
       ] [ --output-file outfile ]

DESCRIPTION

       GeoidEval reads in positions on standard input and prints out the corresponding geoid
       heights on standard output.  Optionally, it also prints the northerly and easterly
       gradients of the geoid height.

       Positions are given as latitude and longitude, UTM/UPS, or MGRS, in any of the formats
       accepted by GeoConvert(1).  (MGRS coordinates signify the center of the corresponding MGRS
       square.)  If the -z option is specified then the specified zone is prepended to each line
       of input (which must be in UTM/UPS coordinates).  This allows a file with UTM eastings and
       northings in a single zone to be used as standard input.

       More accurate results for the geoid height are provided by Gravity(1).  This utility can
       also compute the direction of gravity accurately.

OPTIONS

-n use geoid name instead of the default "egm96-5". See GEOIDS.

-d read geoid data from dir instead of the default. See GEOIDS.

-l use bilinear interpolation instead of cubic. See INTERPOLATION.

-a cache the entire data set in memory. See CACHE.

-c cache the data bounded by south west north east in memory. See CACHE.

-g print the northerly and easterly gradients after the geoid height (i.e., the rate at
which the geoid height changes per unit distance along the WGS84 ellipsoid in the
specified directions). As a result of the way that the geoid data is stored, the
calculation of gradients can result in large quantization errors. This is
particularly acute at high latitudes and for the easterly gradient.

-z prefix each line of input by zone, e.g., "38N". This should be used when the input
consists of UTM/UPS eastings and northings.

--msltohae
standard input should include a final token on each line which is treated as a height
(in meters) above the geoid and the output echoes the input line with the height
converted to height above ellipsoid (HAE). If -z zone is specified then the third
token is treated as the height; this makes it possible to convert LIDAR data where
each line consists of: easting northing height intensity.

--haetomsl
this is similar to --msltohae except that the height token is treated as a height (in
meters) above the ellipsoid and the output echoes the input line with the height
converted to height above the geoid (MSL).

-v print information about the geoid on standard error before processing the input.

--comment-delimiter
set the comment delimiter to commentdelim (e.g., "#" or "//"). If set, the input
lines will be scanned for this delimiter and, if found, the delimiter and the rest of
the line will be removed prior to processing and subsequently appended to the output
line (separated by a space).

--version
print version and exit.

-h print usage, the default geoid path and name, and exit.

--help
print full documentation and exit.

--input-file
read input from the file infile instead of from standard input; a file name of "-"
stands for standard input.

--input-string
read input from the string instring instead of from standard input. All occurrences
of the line separator character (default is a semicolon) in instring are converted to
newlines before the reading begins.

--line-separator
set the line separator character to linesep. By default this is a semicolon.

--output-file
write output to the file outfile instead of to standard output; a file name of "-"
stands for standard output.

GEOIDS

       GeoidEval computes geoid heights by interpolating on the data in a regularly spaced table
       (see INTERPOLATION).  The following geoid tables are available (however, some may not be
       installed):

                                         bilinear error    cubic error
          name         geoid    grid     max      rms      max      rms
          egm84-30     EGM84    30'      1.546 m  70 mm    0.274 m  14 mm
          egm84-15     EGM84    15'      0.413 m  18 mm    0.021 m  1.2 mm
          egm96-15     EGM96    15'      1.152 m  40 mm    0.169 m  7.0 mm
          egm96-5      EGM96     5'      0.140 m  4.6 mm   .0032 m  0.7 mm
          egm2008-5    EGM2008   5'      0.478 m  12 mm    0.294 m  4.5 mm
          egm2008-2_5  EGM2008   2.5'    0.135 m  3.2 mm   0.031 m  0.8 mm
          egm2008-1    EGM2008   1'      0.025 m  0.8 mm   .0022 m  0.7 mm

       By default, the "egm96-5" geoid is used.  This may changed by setting the environment
       variable "GEOID_NAME" or with the -n option.  The errors listed here are estimates of the
       quantization and interpolation errors in the reported heights compared to the specified
       geoid.

       The geoid data will be loaded from a directory specified at compile time.  This may
       changed by setting the environment variables "GEOID_PATH" or "GEOGRAPHICLIB_DATA", or with
       the -d option.  The -h option prints the default geoid path and name.  Use the -v option
       to ascertain the full path name of the data file.

       Instructions for downloading and installing geoid data are available at
       <http://geographiclib.sf.net/html/geoid.html#geoidinst>.

       NOTE: all the geoids above apply to the WGS84 ellipsoid (a = 6378137 m, f =
       1/298.257223563) only.

INTERPOLATION

       Cubic interpolation is used to compute the geoid height unless -l is specified in which
       case bilinear interpolation is used.  The cubic interpolation is based on a least-squares
       fit of a cubic polynomial to a 12-point stencil

          . 1 1 .
          1 2 2 1
          1 2 2 1
          . 1 1 .

       The cubic is constrained to be independent of longitude when evaluating the height at one
       of the poles.  Cubic interpolation is considerably more accurate than bilinear; however it
       results in small discontinuities in the returned height on cell boundaries.  The gradients
       are computed by differentiating the interpolated results.

CACHE

       By default, the data file is randomly read to compute the geoid heights at the input
       positions.  Usually this is sufficient for interactive use.  If many heights are to be
       computed, use -c south west north east to notify GeoidEval to read a rectangle of data
       into memory; heights within the this rectangle can then be computed without any disk
       access.  If -a is specified all the geoid data is read; in the case of "egm2008-1", this
       requires about 0.5 GB of RAM.  The evaluation of heights outside the cached area causes
       the necessary data to be read from disk.  Use the -v option to verify the size of the
       cache.

       Regardless of whether any cache is requested (with the -a or -c options), the data for the
       last grid cell in cached.  This allows the geoid height along a continuous path to be
       returned with little disk overhead.

ENVIRONMENT

       GEOID_NAME
           Override the compile-time default geoid name of "egm96-5".  The -h option reports the
           value of GEOID_NAME, if defined, otherwise it reports the compile-time value.  If the
           -n name option is used, then name takes precedence.

       GEOID_PATH
           Override the compile-time default geoid path.  This is typically
           "/usr/local/share/GeographicLib/geoids" on Unix-like systems and "C:/Documents and
           Settings/All Users/Application Data/GeographicLib/geoids" on Windows systems.  The -h
           option reports the value of GEOID_PATH, if defined, otherwise it reports the compile-
           time value.  If the -d dir option is used, then dir takes precedence.

       GEOGRAPHICLIB_DATA
           Another way of overriding the compile-time default magnetic path.  If it is set (and
           if MAGNETIC_PATH is not set), then $GEOGRAPHICLIB_DATA/magnetic is used.

ERRORS

       An illegal line of input will print an error message to standard output beginning with
       "ERROR:" and causes GeoidEval to return an exit code of 1.  However, an error does not
       cause GeoidEval to terminate; following lines will be converted.

ABBREVIATIONS

       The geoid is usually approximated by an "earth gravity model". The models published by the
       NGA are:

       EGM84
           An earth gravity model published by the NGA in 1984,
           http://earth-info.nga.mil/GandG/wgs84/gravitymod/wgs84_180/wgs84_180.html
           <http://earth-info.nga.mil/GandG/wgs84/gravitymod/wgs84_180/wgs84_180.html>.

       EGM96
           An earth gravity model published by the NGA in 1996,
           http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm96/egm96.html <http://earth-
           info.nga.mil/GandG/wgs84/gravitymod/egm96/egm96.html>.

       EGM2008
           An earth gravity model published by the NGA in 2008,
           http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm2008 <http://earth-
           info.nga.mil/GandG/wgs84/gravitymod/egm2008>.

       WGS84
           World Geodetic System 1984, <http://en.wikipedia.org/wiki/WGS84>.

       HAE Height above the WGS84 ellipsoid.

       MSL Mean sea level, used as a convenient short hand for the geoid.  (However, typically,
           the geoid differs by a few meters from mean sea level.)

EXAMPLES

       The height of the EGM96 geoid at Timbuktu

           echo 16:46:33N 3:00:34W | GeoidEval
           => 28.7068 -0.02e-6 -1.73e-6

       The first number returned is the height of the geoid and the 2nd and 3rd are its slopes in
       the northerly and easterly directions.

       Convert a point in UTM zone 18N from MSL to HAE

          echo 531595 4468135 23 | GeoidEval --msltohae -z 18N
          => 531595 4468135 -10.842

AUTHOR

       GeoidEval was written by Charles Karney.

HISTORY

       GeoidEval was added to GeographicLib, <http://geographiclib.sf.net>, in 2009-09.