Old File Formats

Old CPT file formats can be read by CPT10. Their structure is simpler than the new formats, and so some users may prefer to continue to use the old format.

Gridded data files must be structured such that columns represent longitudes, and rows represent latitudes. The date, the latitudes and the longitudes must also be provided. The first row of data must indicate the date of the first record in the format dd mmm yyyy, followed by the longitudes. The second record must contain the latitude followed by the data. Latitudes must be represented as between 90 and -90, with negative values indicating latitudes in the southern hemisphere. It is more slightly efficient to order the latitudes from north to south, but the reverse ordering can be used. Longitudes must be represented as values between -180 and +360, with negative values indicating longitudes in the western hemisphere, and the longitudes must be ordered from west to east. Hence, a portion of a 2.5 degree gridded input file should look something like the following:

01 Aug 1968       0.000000         2.50000         5.00000         7.50000
   88.7500         2854.78         2855.14         2855.50         2855.85
   86.2500         2854.08         2855.04         2855.96         2856.86
   83.7500         2856.63         2858.27         2859.79         2861.19

Station data files must be structured such that each column represents a different station, and each row represents the observed values for a given year. However, the first three rows must include the station name or label (maximum of 16 characters with no space in the middle of a name of label), latitude and longitude, respectively, of each station, and must be preceded by the keywords "Station" (or "Stn"), "Latitude" (or "Lat"), and "Longitude" (or "Long" or "Lon"). The keywords are not case-sensitive, and so can be in upper, or lower, or mixed case. The first column of the data file must represent the year, listed consecutively beneath the keywords. (For applications in which the data do not represent years it would normally be appropriate to set this column to the record number.) Hence, a valid station input file should look something like the following:

STN   STN_A STN_B STN_C STN_D STN_E STN_F
LAT    10.0  12.2  11.5   8.2   9.4  10.9
LONG   -1.0  12.3 -10.2   9.1  -5.3   8.4
1965   0.44  0.09  0.29  0.03  0.06  0.43
1966   0.18  0.34  0.81  1.96  1.09  0.51
1967   1.57  1.00  1.07  1.19  1.61  1.13
1968   0.77  0.99  0.35  0.76  0.52  0.29

Unreferenced data files are similar to the station data files, but do not have the first second and third rows, and use the "Name" keyword (again not case-sensitive) instead of the "Station" keyword. ("Year" and "Years" are acceptable alternative keywords.) Thus, unreferenced data files should be structured such that each column represents a different series, and each row represents the observed values for a given year. The first row of the file should indicate the name of each series (maximum of 16 characters with no space in the middle of a name of label). The first column of the data file must represent the year, listed consecutively beneath the "Name" keyword. (For applications in which the data do not represent years it would normally be appropriate to set this column to the record number.) Hence, a valid unreferenced input file should look something like the following:

NAME      A     B     C     D     E     F
1965   0.44  0.09  0.29  0.03  0.06  0.43
1966   0.18  0.34  0.81  1.96  1.09  0.51
1967   1.57  1.00  1.07  1.19  1.61  1.13
1968   0.77  0.99  0.35  0.76  0.52  0.29

Since version 6 of CPT it is no longer permissible for the grid points, stations or series to run over to the following line.