cdm/src/main/java/ucar/unidata/geoloc/LatLonPointImpl.java
static public double lonNormalFrom(double lon, double start) {
    while (lon < start) lon += 360;
    while (lon > start+360) lon -= 360;
    return lon;
  }
static public double lonNormalFrom(double lon, double start) {
    while (lon < start) lon += 360;
    while (lon > start+360) lon -= 360;
    return lon;
  }
put longitude into the range [start, start+360] deg

@param lon    lon to normalize
@param start starting point
@return longitude into the [start, start+360] deg