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Save this file as a .csv file. Then open this .csv file in a text editor. It should look like this:
5
-123.3, 45.0, -72
-123.4, 45.1, -72
-123.5, 45.2, -72
-123.6, 45.3, -72
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Remove any extra commas. Rename the file from yourfilename.csv to yourfilename.dat.
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