Arjen Markus (6 july 2009) NetCDF files are a popular way of distributing scientific data (results of numerical models or satellite data for instance). The library (found at for instance http://www.unidata.ucar.edu/software/netcdf/ ) is easy enough to use and there exist (at least?) two Tcl interfaces to it. Unfortunately, one has not been maintained over the years and the other is part of NAP, a very nice extension, but it means you have to deal with NAP's data model. If you just want to store and retrieve data structured as a block, then the geographical coordinates may be a hindrance.
So, here are the very humble beginnings of an extension that uses Critcl to read and write NetCDF files in a more basic way. I intend to add a higher-level API (and note: it does not yet retrieve the actual data ...)
# bindnetcdf.tcl --
# Humble start of Tcl bindings for NetCDF
#
package require critcl
critcl::config keepsrc 1
critcl::config force 1
#
# NOTE: Windows-specific!
#
critcl::clibraries netcdf.lib
#critcl::config I [pwd]
set env(HOME) .
critcl::ccode {
#include <stdlib.h>
#include "netcdf.h"
}
critcl::cproc nc_create {Tcl_Interp* ip char* fileName} ok {
int ncid;
int retval;
retval = nc_create( fileName, NC_CLOBBER, &ncid );
if ( retval == 0 ) {
Tcl_SetObjResult( ip, Tcl_NewIntObj(ncid) );
return TCL_OK;
} else {
Tcl_SetResult( ip, (char *) nc_strerror(retval), TCL_VOLATILE );
return TCL_ERROR;
}
}
critcl::cproc nc_close {Tcl_Interp* ip int ncid} ok {
int retval;
retval = nc_close( ncid );
if ( retval == 0 ) {
Tcl_SetObjResult( ip, Tcl_NewIntObj(ncid) );
return TCL_OK;
} else {
Tcl_SetResult( ip, (char *) nc_strerror(retval), TCL_VOLATILE );
return TCL_ERROR;
}
}
critcl::cproc nc_enddef {Tcl_Interp* ip int ncid} ok {
int retval;
retval = nc_enddef( ncid );
if ( retval == 0 ) {
return TCL_OK;
} else {
Tcl_SetResult( ip, (char *) nc_strerror(retval), TCL_VOLATILE );
return TCL_ERROR;
}
}
critcl::cproc nc_def_dim {Tcl_Interp* ip int ncid char* dimName int dim} ok {
int retval;
int dimid;
if ( dim <= 0 ) {
dim = NC_UNLIMITED;
}
retval = nc_def_dim( ncid, dimName, dim, &dimid );
if ( retval == 0 ) {
Tcl_SetObjResult( ip, Tcl_NewIntObj(dimid) );
return TCL_OK;
} else {
Tcl_SetResult( ip, (char *) nc_strerror(retval), TCL_VOLATILE );
return TCL_ERROR;
}
}
critcl::cproc nc_def_var {Tcl_Interp* ip int ncid char* varName char* type
Tcl_Obj* dims} ok {
int retval;
int typeCode;
int varid;
int dimid;
int dimids[10];
int ndim;
int i;
Tcl_Obj *elemObj;
/* Extract the IDs of the dimension variables
*/
retval = Tcl_ListObjLength( ip, dims, &ndim );
if ( retval != TCL_OK ) {
return retval;
}
if ( ndim > 10 ) {
Tcl_SetResult( ip, "Too many dimensions specified!", TCL_STATIC );
return TCL_ERROR;
}
for ( i = 0; i < ndim; i ++ ) {
retval = Tcl_ListObjIndex( ip, dims, i, &elemObj );
if ( retval != TCL_OK ) {
return retval;
}
retval = Tcl_GetIntFromObj( ip, elemObj, &dimids[i] );
if ( retval != TCL_OK ) {
return retval;
}
}
typeCode = -1;
if ( strcmp( type, "int" ) == 0 ) typeCode = NC_INT;
if ( strcmp( type, "long" ) == 0 ) typeCode = NC_LONG;
if ( strcmp( type, "float" ) == 0 ) typeCode = NC_FLOAT;
if ( strcmp( type, "double" ) == 0 ) typeCode = NC_DOUBLE;
if ( typeCode == -1 ) {
Tcl_SetResult( ip, "Invalid type specified!", TCL_STATIC );
return TCL_ERROR;
}
retval = nc_def_var( ncid, varName, typeCode, ndim, dimids, &varid );
if ( retval == 0 ) {
Tcl_SetObjResult( ip, Tcl_NewIntObj(varid) );
return TCL_OK;
} else {
Tcl_SetResult( ip, (char *) nc_strerror(retval), TCL_VOLATILE );
return TCL_ERROR;
}
}
critcl::cproc nc_put_att_text {Tcl_Interp* ip int ncid int varid
char* attName char* attValue} ok {
int retval;
retval = nc_put_att_text( ncid, varid, attName, strlen(attValue), attValue);
if ( retval == 0 ) {
return TCL_OK;
} else {
Tcl_SetResult( ip, (char *) nc_strerror(retval), TCL_VOLATILE );
return TCL_ERROR;
}
return TCL_ERROR;
}
critcl::cproc nc_get_var {Tcl_Interp* ip int ncid char* varName} ok {
/* TODO
int retval;
int dimid;
retval = nc_get_dim( ncid, varName, &varid );
if ( retval == 0 ) {
Tcl_SetObjResult( ip, Tcl_NewIntObj(varid) );
return TCL_OK;
} else {
Tcl_SetResult( ip, (char *) nc_strerror(retval), TCL_VOLATILE );
return TCL_ERROR;
}
*/
return TCL_ERROR;
}
critcl::cproc nc_inq_varname {Tcl_Interp* ip int ncid int varid} ok {
int retval;
int dimid;
char varName[NC_MAX_NAME+1];
retval = nc_inq_varname( ncid, varid, &varName );
if ( retval == 0 ) {
Tcl_SetObjResult( ip, Tcl_NewStringObj(varName, -1) );
return TCL_OK;
} else {
Tcl_SetResult( ip, (char *) nc_strerror(retval), TCL_VOLATILE );
return TCL_ERROR;
}
return TCL_ERROR;
}
# main --
# Test the thing
#
set ncid [nc_create "somefile.nc"]
set xdimid [nc_def_dim $ncid "X" 10]
set ydimid [nc_def_dim $ncid "Y" 20]
set xvarid [nc_def_var $ncid "X" float $xdimid]
set yvarid [nc_def_var $ncid "Y" float $ydimid]
set salin [nc_def_var $ncid "Salinity" float [list $xdimid $ydimid]]
puts "$xdimid -- $ydimid"
catch {
nc_put_att_text $ncid $xdimid name "X-coordinate"
} msg
puts "NC: $msg"
set err 0
set i 0
while { $err == 0 } {
set err [catch {
puts [nc_inq_varname $ncid $i]
} msg]
incr i
}
nc_close $ncid