I have a netCDF file that contains climate data in a Gaussian grid. The longitudes are given from 0 to 360. I need to convert this to -180 to 180.

Is this the correct formula -

If longitude is greater than 180 subtract 360

I am looking to do this in Fortran.

2 Answers 2


Here is an example for fortran:

Variables in explanation:

long1 is the longitude varying from -180 to 180 or 180W-180E
long3 is the longitude variable from 0 to 360 (all positive)

To convert longitude from (0-360) to (-180 to 180)

 Matlab and fortran long1=mod((long3+180),360)-180

 Matlab long1=rem((long3+180),360)-180

 Fortran long1=modulo((long3+180),360)-180

To convert longitude from (-180 to 180) to (0-360)

 Matlab lon3=mod(lon1,360)

 Fortran lon3=modulo(lon1,360)

The “mod” function is Fortran is equivalent to “rem” function in Matlab.

The “modulo” function in Fortran is equivalent to “mod” function in Matlab.



If you know for certain that your input longitudes range between 0 and 360, then yes: just subtract 360 from values that are greater than (or equal to) 180.

If there is any possibility of "crazy" values (less than -180 or greater than 540) you might consider using the IEEE_REM function:

fixed_longitude = IEEE_REM(longitude, 360.0)

This will gracefully handle any longitude value with no other logic required.

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