Re: "GEMPAK map files document"

Stonie,

See below.
You should have the $GEMMAPS/programs directory with sources for ssfgsf
and gsfssf if you need additional references.

******************************************************************


                         GEMPAK MAP FILES


GEMPAK map files are stored as direct access, packed binary files in
a GEMPAK Standard Format (GSF).  This form was chosen for compactness
and relatively rapid access.

In addition, a Sequential Standard Format (SSF) is defined for storing
maps as ASCII sequential files.  SSF files are used to create new maps,
edit existing map files and transfer map files between computer
systems.  Since these are ASCII files, they may be created or changed
using a text editor.  The SSF files use the same format as the NCAR
sequential map file.

In both the GSF and SSF formats, latitude and longitude are given in
degrees.  West longitude is negative; all longitudes must be between
-180 and +180 degrees.  No map segment should cross the International
Date Line.

FORMAT OF THE SSF FILE:

An SSF file contains map segments, each of which has a series of
latitude / longitude points to be connected when the map is drawn.
Each segment contains the following information:

        NP2          INTEGER      Number of points (np) * 2
        RMXLT        REAL         Maximum latitude in segment
        RMNLT        REAL         Minimum latitude in segment
        RMXLN        REAL         Maximum longitude in segment
        RMNLN        REAL         Minimum longitude in segment
        PTS (NP2)    REAL         LAT1 LON1 ... LATnp LONnp

These segments are written and read with the FORTRAN format statement:

        FORMAT  ( I4, 14X, 6F9.3, 8X, / ( 8F9.3, 8X ) )

The maximum number of points which may be contained in any segment
is 3000.


FORMAT OF THE GSF FILE:

These files are direct access file with a recordsize of 128 words.
The data is written in blocks of two records or 256 words.  The first
block is the file header, followed by data blocks.  Map segments are
packed into the data blocks; no map segment spans blocks.

The file header has 181 INTEGER*2 words containing:

        NMBLK        INTEGER*2    Total number of blocks
        LATPTR1      INTEGER*2    Latitude pointer for 90 degrees
        LATPTR2      INTEGER*2    Latitude pointer for 89 degrees
          ...
        LATPTR180    INTEGER*2    Latitude pointer for -89 degrees

The GSF files are sorted by maximum latitude.  The LATPTR array
contains the first block to use given the maximum latitude on the
plot.

These INTEGER*2 values may be changed to INTEGER*4 if required.
However, the changes must be made in the programs GSFSSF and SSFGSF
described below, as well as in GDRMAP which is the GEMPLT subroutine
used to draw maps.

The data blocks contain only 4-byte integer or real words.  Each
data block contains:

        NMSEG        INTEGER      Number of segments
        -----        ------       Unused
        NP1          INTEGER      Number of points in segment 1
        RMNLT1       REAL         Minimum latitude
        RMNLN1       REAL         Minimum longitude
        RMXLT1       REAL         Maximum latitude
        RMXLN1       REAL         Maximum longitude
        -----        ------       Unused
        RLAT1 (1)    REAL         Latitude of point 1
        RLON1 (1)    REAL         Longitude of point 1
         ...
        RLAT1 (np1)  REAL         Latitude of point np1
        RLON1 (np1)  REAL         Longitude of point np1
        NP2          INTEGER      Number of points in segment 2
        RMNLT1       REAL         Minimum latitude
         ...


CONVERTING A GSF TO AN SSF FILE:

The program GSFSSF, which is in $GEMMAPS/programs, can be used to
convert any GSF file to an SSF file.  The user is prompted for the
existing GSF file name and a name for the SSF file to be created.


CONVERTING AN SSF FILE TO A GSF FILE:

The program SSFGSF, also in $GEMMAPS/programs, can be used to convert
an SSF file to a GSF file.  The user is prompted for the existing SSF
file name and a name for the GSF file to be created.  The user can also
enter a latitude / longitude window to subset the data.  Any points
outside the window will be eliminated from the output file.  However,
no clipping is done.  The minimum and maximum latitude and longitude
stored with each segment will be recomputed internally, so the
values in the SSF file need not be correct.  The intermediate files,
DAFIL.INT and SEQFIL.INT, are used by the program and may be deleted
after completion.


NAMING CONVENTIONS FOR GEMPAK MAP FILES:

The map files are named by concatenating the resolution, map
boundaries, and area with the three-letter source file type.  For
example, the medium-resolution political world map from Goddard
Space Flight Center is called MEPOWO.GSF.

  RESOLUTION         FEATURES             AREA           SOURCE

    ToP         POlitical             WOrld             GSFc
    HIgh        COastline             NW quadrant       NWS
    MEdium      REgional              NE quadrant       CIA
    LOw         CouNty                SE quadrant       USGeol survey
    MiXed       CountrY               SW quadrant       NCeP
                RiVers                North Hemisphere  RFC
                InterState highways   South Hemisphere  CPC
                U.s. Highways         US
                State Highways        Us Oceans
                RoaDs                 North America
                River Forecast Cntrs  Atlantic North
                County Watch Areas    Atlantic1
                ZoNes                 Atlantic2
                High Seas             Atlantic3
                OffShore              Pacific North
                Forecast Bounds       Pacific East
                AViation              Pacific Surface
                Flight Info region    Pacific1
                Convective Sigmet Reg Pacific2
                Tpc High seas         Pacific3
                Tpc Sigmets           MarylanD
                Tpc surface Bounds    Basic Weather
                Tpc surface Analysis  Medium Range
                Tpc aViation bounds   Qpf Verification
                Continental Divide    Western Region
                Mar pred ctr Offshore Arkansas-Red Basin
                River fcst ctr Basins Lower Mississippi
                Climate Zones         Middle Atlantic
                Palmer climate Zones  Missouri Basin
                STates                North Central
                LaKes                 NorthEast
                                      OHio
                                      SouthEast
                                      West Gulf
                                      AlasKa

The maps from GSFC were obtained for GEMPAK Version 1.0.  The history
of these maps is unknown.  The CIA map files were created from a
subset of the CIA map database.  The United States Geological Survey
maps were converted from the USGS databases.  The NWS maps were
obtained from the NWS/Modernization Systems Implementation Group.  The
NCEP map files were developed at the NWS/National Centers for
Environmental Prediction.  The RFC map files were provided by the
Arkansas-Red Basin River Forecast Center.

There are 5 maps designed to be used for the seamless surface analysis
which shows the area of responsibility for the Tropical Prediction
Center, Marine Prediction Center and the Hydrometeorological Prediction
Center. Also, these maps have the numbers 050 and 215 in their names
which refer to the amount of time after the analysis time; 50 minutes
past and 2 hours and 15 minutes past the analysis time.


CIA MAP FILE WITH NAMES:

A subset of the CIA map database which has a geographical name attached
to each record is included in the complement of GEMPAK maps.  The names
in this file were originally added by Joseph Fulson-Woytek at Goddard
Space Flight Center.  The map file name is:  cia.nam.

The program NAMSSF is included to convert a subset of this database
into a sequential format file (SSF).  The program will prompt for the
following inputs:

     AREA:     This may be any geographic name or a range of
               records specified by the start and stop records separated
               with a "-".

     REGION:   A character string listing the regions to be used (a
               blank defaults to all) where the valid regions are:

                   C  -  Continental borders
                   I  -  Islands
                   L  -  Lakes
                   S  -  State borders
                   N  -  National borders
                   R  -  Rivers
                   T  -  Tectonic plates
                   M  -  Miscellaneous

Example:  Create a map containing only Mexico borders

          AREA:    mexico
          REGION:  cn

          Note that adding S will include "New Mexico" and I will
          include "Gulf of Mexico Islands".

The program NAMPLT will plot individual records listing the record
and waiting for a <CR> after each record.  This can be used for
debugging the map file.  GPMAP must be run first to select the
graphics area and device.

The files doc.nam and rec.nam include the detailed documentation
and a list of records for the map elements, respectively.  If changes
are made to the data base, they should be returned to the GEMPAK
developers in order to be included in the original dataset from which
the map file was created.

*******************************************************



Steve Chiswell



On Thu, 21 Aug 2003, Stonie R. Cooper wrote:

> Clint,
>
> How are things going for you?  I hope well . . .
>
> I did a search on the web for a mysterious "GEMPAK map files document" so I
> could create some custom maps for GEMPAK . . . and came across a reference
> that you had looked for . . . and found . . . the same thing I'm looking for.
>
> Would you mind sharing where you found it?  I don't have any ascii map files
> in my distro of GEMPAK (5.6.j), so they must have removed them to save space
> . . . but now, no doc that I can find.
>
> Thanks in advance for any pointers.
> --
> Stonie R. Cooper
> Planetary Data, Incorporated
> (402) 782-6611
>