INFORMATION FILE FOR GRIDDED DATA TRANSFER DIRECTORY

This directory contains subdirectories for ascii and binary gridded
files of the Texas merged aeromagnetic and gravity data.  Each data 
grid is available in 4 different data formats:

1. GXF  - GeoSoft GXF format (an ascii grid exchange format)
2. ERM  - ER Mapper grid format (a two-file transfer format)
3. ARC  - ArcInfo e00 binary grid export format
4. ODDF - USGS ODDF (version 1.6.1) grid format (a binary format)

Each of these formats is discussed briefly below. If none of these 
formats is directly readable by software on your system, then the 
GXF format is most easily modified by inputting and translation.  
Extensive description of this format is given below.

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Projection:  Lambert Conformal Conic
Datum: NAD-27-USA
Ellipsoid: Clarke 1866
Parameters:
1st standard parallel:  33° N. 
2nd standard parallel:  45° N.
Central meridian:     -100° W. longitude
Latitude of projection's origin:   0° N. latitude
False easting (meters)     0.00000
False northing (meters)    0.00000
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1. Grid eXchange Format (GXF)

GXF (Grid eXchange File) is a standard ASCII file format for
exchanging gridded data among different software systems. 
Software that supports the GXF standard will be able to import
properly formatted GXF files and export grids in GXF format.

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2. ER Mapper grid format (ers)

The ER Mapper grid format consists of two files: a binary data
file  (no file suffix) and an ascii header file (*_ers).  These
files can be read directly by the ER Mapper software or by other
packages such as ERDAS IMAGINE.  Note that the header files refer
to the projection as "RAW", indicating that the projection 
information and format must be defined by the user. 

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3.  ArcInfo grid export format (e00)

This format is readable by ArcInfo, ERDAS Imagine, and other
packages.  When imported into ArcInfo, this file will unpack
into a directory containing all the components of the registered
grid coverage.

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4. USGS ODDF binary grid format (grd)

This is a binary format with an included ascii header.  This
format is used by the USGS Geophysics Group within the Minerals
Program of the Geologic Division.   The ascii header gives all
information necessary to convert this file to another format.

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