shape - GrADS Extensions for Shapefile support

NAME

shape - GrADS Extensions for Shapefile support

SYNOPSIS

shp_polyf SHAPEFILE [OBJECT]

shp_lines SHAPEFILE [OBJECT]

shp_print SHAPEFILE

DESCRIPTION

This library of GrADS extensions provides commands for the display and output of shapefiles. Quoting from the Shapefile C Library documentation by Frank Warmerdam:

The Shapefile format is a new working and interchange format promulagated by ESRI (http://www.esri.com/) for simple vector data with attributes. It is apparently the only file format that can be edited in ARCView 2/3, and can also be exported and imported in Arc/Info. An excellent white paper on the shapefile format is available from ESRI:

        http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf

The file format actually consists of three files.

 XXX.shp - holds the actual vertices.
 XXX.shx - hold index data pointing to the structures in XXX.shp
 XXX.dbf - holds the attributes in xBase (dBase) format.

COMMANDS PROVIDED

shp_polyf SHAPEFILE [OBJECT]

For each polygon object defined in SHAPEFILE, a filled polygon is plotted as overlay on GrADS plots using the current line attributes. Optionally, one can specify a particular OBJECT to plot.

shp_lines SHAPEFILE [OBJECT]

Each object contained in SHAPEFILE is plotted as a continous line joining vertexes as overlay on GrADS plots using the current line attributes. Optionally, one can specify a particular OBJECT to plot.

shp_print SHAPEFILE

This function has NOT been implemented yet.

OBTAINING SHAPEFILES

Here is a very partial list of free (as in beer) shapefiles, as well for a DVD that you can buy. We do not support or endorse these products, we list them here for reference only.

Suggested Installation Procedure

We recommend that you install each triplet (XXX.shp,XXX.shx,XXX.dbf) of files in your GrADS data directory (GADDIR), along with the other font and map databases. This way you will be able to refer to them without entering the full pathname.

ESRI First Level World Administrative Boundaries 1998

This shapefile contains the political boundaries for each country, and states/provinces within each country as of 1998. The data is freely available from:

 http://geodata.grid.unep.ch/download/admin98_li_shp.zip

GSHHS - A Global Self-consistent, Hierarchical, High-resolution Shoreline Database

GSHHS contain contains shapefiles of varying complexity:

gshhs_land

contains the basic coastline shapefile

gshhs_lake

contains the shapefile of lakes within land

gshhs_isl

contains the shapefile of islands within lakes

gshhs_pond

contains the shapefile of ponds within islands within lakes

The data is freely available from NOAA:

   http://www.ngdc.noaa.gov/mgg/shorelines/data/gshhs/version1.5/shapefiles/

FAO GeoNetwork

The GeoNetwork opensource allows to easily share geographically referenced thematic information between different FAO Units, other UN Agencies, NGO's and other institutions. You can find more information here:

   http://www.fao.org/geonetwork/srv/en/main.home

For example, if you search for Administrative Boundaries shapefile in this site you get a list of administrative boundaries for many countries.

American Geological Institute Global GIS DVD

This DVD is a product of an agreement between the U.S. Geological Survey (USGS) and The American Geological Institute (AGI) for making the USGS Global Geographic Information System (GIS) database readily available to educators and the general public in the form of a DVD based world atlas. Quoting from the AGI website:

   The USGS Global GIS database contains a wealth of USGS and other
   public domain data, including global coverages of elevation,
   landcover, seismicity, and resources of minerals and energy at a
   nominal scale of 1:1 million

Unfortunately, this DVD is not free and carries a restrictive license. You can obtain additional information here:

   http://www.agiweb.org/pubs/globalgis/index.html

If you know of another good source of shapefiles...

Please drop us a note.

EXAMPLES

For trying these examples you will need to download the freely available ESRI First Level World Administrative Boundaries 1998 (see OBTAINING SHAPEFILES above). Place the files

   admin98.dbf
   admin98.shp
   admin98.shx

either in your local directory or in your GrADS data directory GADDIR (recommended.)

Display Administrative Boundaries

Start by disabling the map drawing by GrADS

   ga-> set mpdraw off

Then display something and add a new map:

   ga-> d ts
   ga-> shp_lines admin98

Display a Solid Basemap

Similarly,

   ga-> d ts
   ga-> shp_polyf admin98

Changing the color of the map

You can use the set line command of GrADS to change the color, thickness and line style of the shapefile being drawn:

   ga-> set line 9
   ga-> shp_lines admin98

will plot the map in magenta. See the GrADS documentation for more information.

BUGS

Only shapefiles having longitude/latitude coordinates are supported. Shapefiles in UTM coordinates cannot yet be read by this extension. The work around is to convert your shapefile to lat/lon using an utility such as ogr2ogr that comes with GDAL:

    http://www.gdal.org/

CREDITS

Graziano Giuliani wrote the first version of shp_polyf() as a bult-in patch for GrADS v1.b4. Arlindo da Silva converted it to a GrADS extension and introduced shp_print() based on his gxyat utility; as of this writing shp_print() is just a stub.

The Shapefile C Library by Frank Warmerdam is extensively used for the manipulation of shapefiles.

COPYRIGHT

Copyright (c) 2007 Graziano Giuliani

Copyright (c) 2007 Arlindo da Silva

This is free software released under the GNU General Public License; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

 shape - GrADS Extensions for Shapefile support