Grid export format (.gxf).  A description of GXF format follows.
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Projection:  Lambert Conformal Conic
Datum: NAD-27-USA
Ellipsoid: Clarke 1866
Base Latitude: 0
Central Meridian: -100
Standard Parallels: 33 N. and 45 N.
Major Axis: 6378206.4
Eccentricity: 0.08227185422
Prime Meridian: 0
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texas_mag file:

No. of Columns:  1364                                                                       
No. of Rows:   1268                                         
Origin of all grids: -658000 meters East 315800 meters North
Grid Interval:  1000 meters
Location of the grid value within the cell: lower left corner
Rotation:  None
Dummy value:  -9999.000


texas_cbggrav and texas_isograv files:

No. of Columns:  658                                                                       
No. of Rows:   602                                         
Origin of all grids: -666000 meters East 316800 meters North
Grid Interval:  2000 meters
Location of the grid value within the cell: lower left corner
Rotation:  None
Dummy value:  -9999.000

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Grid eXchange Format (.gxf files) 
 
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. 
 
Grid Description:
 
A grid is a rectangular array of points at which single data values
define a two dimensional function. Grid point locations are related 
to a Grid Coordinate System (GCS), which is a right-handed Cartesian 
system with X and Y axis defined by the bottom and left sides of a grid 
array.  The grid point at the bottom, left corner of the array is the 
origin of the GCS.  All distances are in meters. 
 
GCS coordinates are related to a Base Coordinate System (BCS) through 
a plane translation and rotation.  The origin of the GCS is located at 
point (X0,Y0) in the BCS, and the X and Y grid indices are related to 
BCS units through the separation between points in the GCS X and Y 
directions. 
 
Labeled Data Objects and Comments: 
 
A GXF file is an ASCII file made up of a number of labeled data objects
and comments.  Each labeled data object has a label line followed by one 
or more data lines.  A label line is identified by a '#' character in 
the first column followed immediately by an upper-case label.  The data 
associated with that label are found on one or more lines that follow 
the label. 
 
Lines:
 
All lines in a GXF file must be less than or equal to 80 characters in 
length. Any lines that are not part of a labeled data object are ignored 
and can be used to place comments within a GXF file.  Programs that read 
GXF files will skip such comment lines while they search for the next 
GXF data object.
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GXF Object Definitions:
 
#TITLE 
A one line descriptive title of the grid.  Some grid formats include 
textual descriptions of the grid, and this information can be placed 
in a #TITLE object. 
Default:	blank title 
 
#POINTS 
The number of points in each grid row (horizontal or vertical as 
defined by the #SENSE object). 
Default:	no default - this object is required. 
 
#ROWS 
The number of rows in the grid.  A grid row (or vector) is a collection
of consecutive grid points that represent the grid values along a 
horizontal or vertical line in the grid.  The complete grid is then 
defined by a consecutive sequence of grid rows. 
Default:	no default - this object is required. 
 
#PTSEPARATION 
The separation between points in the grid.  This should be in Base 
Coordinate System units (ground units for geographically based grids). 
Default:	1.0 
 
#RWSEPARATION 
The separation between rows in the grid.  These should be in Base 
Coordinate System units (ground units for geographically based grids). 
Default:	1.0 
 
#XORIGIN 
The X location of the bottom left corner of the grid in the Base 
Coordinate System. 
Default:	0.0 
 
#YORIGIN 
The Y location of the bottom left corner of the grid in the Base 
Coordinate System. 
Default:	0.0 
 
#ROTATION 
The rotation angle of the grid.  This is the counter-clockwise angle of
the bottom edge of the grid with respect to the Base Coordinate System 
X axis. Rotation only has meaning for Base Coordinate Systems that use 
the same units on the X and Y axis. 
Default:	0.0 
 
#SENSE 
The first point of the first row of the stored grid can be at any corner 
of the grid rectangle, and the grid rows can be run vertically or 
horizontally. The SENSE object defines this storage sense as follows: 
	 1	first point at bottom left of grid 
	 2	first point at upper left of grid 
	 3	first point at upper right of grid 
	 4	first point at bottom right of grid 
A positive SENSE stores rows in a right-handed sense; a negative SENSE 
stores rows in a left-handed sense.  This means that if you were at the 
first grid point and looking into the grid, the first grid row would 
extend to your right for a right-handed grid (positive sense), or to 
your left for a left-handed grid (negative sense).  (All grids in this 
report have SENSE=+1.) 
Default:	1 (first point at bottom left, rows left to right) 
 
#TRANSFORM 
This keyword is followed by two numbers on the same line:  SCALE and 
OFFSET, which are used to transform the grid data to desired units: 
Z = G * SCALE + OFFSET 
where 
	Z	grid value in the desired unit 
	G	grid values as specified in the #GRID object 
Default:	SCALE = 1.0,  OFFSET = 0.0 
 
#DUMMY 
The grid must be rectangular (every row must have the same number of 
points). The dummy value defined by this object is used to define blank 
areas of the grid.  Any grids that include blank areas must define a 
dummy value. 
Default:	no dummy value. 

#GRID 
The grid data is listed point by point and row by row.  The #GRID object 
and data is always the last object in a GXF file. 
The first data point is at the location indicated by #SENSE, and is 
followed by successive points in that row of points (either horizontal 
or vertical), then the points in the next row, and so on.  The points 
in a row can follow on to the next data line, although each new row must 
start on a new data line.  A GXF reading program can expect #ROWS of 
#POINTS for a total of #ROWS times #POINTS data values. 
Default:	none, must be included as the last object in a GXF file. 
 
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