ACCURACY OF MAPS GENERATED BY NU2MGA30.BAS        22 NOV 96

NU2MGA30.BAS and NU2MGB30.BAS are upgraded revised versions of NU_2MEG. The 
new version implements a more accurate algorithm for converting the grid 
coordinates in the NEW format 1:2,000,000 Scale USGS DLG CDrom. These are 
'chained' BASIC programs. The user enters "qbasic/run numga30" at the DOS 
prompt and responds to a number of questions, following which first NU2MGA30
runs (creating files containing LAT/LON) positional data and then NU2MGB30 
is automatically loaded and run producing the desired .MAP and .DAT files.

NU2MGA30.BAS no longer uses the algorithms of CONV100C.BAS to convert the 
positional information in the USGS DLG files. 

NU2MGA30.BAS now uses a look-up table with linear interpolation to convert 
the coordinate information given in the USGS DLG points into Latitude values. 
This technique and table of values was developed from "Elements of 
Cartography - Third Edition - Arthur H. Robinson. Coordinate information is 
converted to Latitude values using a formula from "Map Projections - 
A Working Manual - USGS Professional Paper 1395, John P. Snyder".

Small residual errors may remain due to the linear approximation and rounding
errors. If this error is significant (to the users of the maps you will be 
producing), you can apply a correction to further reduce the error. Using 
MAPFIX, locate a map feature (road, intersection, lake, QTH, etc.) that you 
know the correct LAT/LON of, under the crosshair, and read its indicated 
LAT/LON. Determine the difference between the indicated and actual LATITUDE. 
Using a text editor, read the origin LATITUDE of your map (first line in the 
.DAT or .MAP file) add the difference (using decimal degrees, not 
degrees/minutes) and change the value in the file. You should use either a 
feature near the center of your map for this or alternatively near the region 
of your map you are most interested in using.


Ted Antanaitis WA7ZZB
email: tedant@pipeline.com
