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API Discussions: |
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================ |
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As discussed in our group meeting of 2003-12-17 (AJA, CNH, JMC, AM, |
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PH, EH3), the NetCDF interface should resemble the following FORTRAN |
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subroutines: |
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|
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1) "stubs" of the form: MNC_WV_[G|L]2D_R[S|L] () |
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2) MNC_INIT_VGRID('V_GRID_TYPE', nx, ny, nz, zc, zg) |
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3) MNC_INIT_HGRID('H_GRID_TYPE', nx, ny, xc, yc, xg, yg) |
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4) MNC_INIT_VAR('file', 'Vname', 'Vunits', 'H_GTYPE', 'V_GTYPE', PREC, FillVal) |
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5) MNC_WRITE_VAR('file', 'Vname', var, bi, bj, myThid) |
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This is a reasonable start but its inflexible since it isn't easily |
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generalized to grids with dimensions other than [2,3,4] or grids with |
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non-horizontal orientations (eg. vertical slices). |
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Generalizing what we would like to write as "variables defined on 1-D |
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to n-D grids", one can imagine a small number of objects containing |
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all the relevant information: |
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a dimension: [ name, size, units ] |
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a grid: [ name, 1+ dim-ref ] |
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a variable: [ name, units, *1* grid-ref, data ] |
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an attribute: [ name, units, data ] |
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a NetCDF file: [ name, 0+ attr, 0+ grid-ref, 0+ var-ref ] |
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which can then be manipulated (created, associated, destroyed, etc.) |
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using a simple interface such as: |
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MNC_INIT( myThid ) |
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MNC_FILE_CREATE( fname, myThid ) |
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MNC_FILE_OPEN( fname, itype, myThid ) |
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MNC_FILE_ADD_ATTR_STR( fname, atname, sval, myThid ) |
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MNC_FILE_ADD_ATTR_DBL( fname, atname, len, dval, myThid ) |
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MNC_FILE_ADD_ATTR_REAL(fname, atname, len, rval, myThid ) |
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MNC_FILE_ADD_ATTR_INT( fname, atname, len, ival, myThid ) |
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MNC_FILE_ADD_ATTR_ANY( fname, atname, atype, cs,len,dv,rv,iv, myThid ) |
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... |
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MNC_FILE_READ_HEADER( fname, myThid ) |
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MNC_DIM_INIT( fname, dname, dlen, myThid ) |
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MNC_GRID_INIT( fname, gname, ndim, dnames, myThid ) |
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MNC_VAR_INIT_DBL( fname, gname, vname, units, myThid ) |
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MNC_VAR_INIT_REAL( fname, gname, vname, units, myThid ) |
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MNC_VAR_INIT_INT( fname, gname, vname, units, myThid ) |
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MNC_VAR_INIT_ANY( fname, gname, vname, units, type, myThid ) |
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MNC_VAR_ADD_ATTR_STR( fname, vname, atname, sval, myThid ) |
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MNC_VAR_ADD_ATTR_DBL( fname, vname, atname, nv, dval, myThid ) |
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MNC_VAR_ADD_ATTR_REAL( fname, vname, atname, nv, rval, myThid ) |
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MNC_VAR_ADD_ATTR_INT( fname, vname, atname, nv, ival, myThid ) |
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MNC_VAR_ADD_ATTR_ANY( fname, vname, atname, atype, cs,len,dv,rv,iv, myThid ) |
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MNC_VAR_WRITE_DBL( fname, vname, var, myThid ) |
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MNC_VAR_WRITE_REAL( fname, vname, var, myThid ) |
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MNC_VAR_WRITE_INT( fname, vname, var, myThid ) |
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MNC_VAR_WRITE_ANY( fname, vname, vtype, dv, rv, iv, myThid ) |
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... |
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MNC_VAR_READ( fname, vname, var, myThid ) |
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MNC_FILE_SYNC( fname, myThid ) |
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MNC_FILE_CLOSE( fname, myThid ) |
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Heres a further "convenience wrapper" written on top of the above UI: |
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MNC_CW_INIT( Gtype, Htype, Hsub, Vtype, Ttype, wHalo, myThid ) |
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with pre-defined - xy - - n |
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combinations: U x c t y |
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'Cen_xy_c_t_Hn' V y i |
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'U_xy_i_t_Hn', Cen |
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'Cor_x_-_-_Hy' Cor |
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MNC_CW_WRITE( myIter, filebn,bi,bj, Gtype, RX, vname, var, myThid ) |
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MNC_CW_READ( myIter, filebn,bi,bj, Gtype, RX, vname, var, myThid ) |
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MNC_CW_RX_W_YY( fbname,bi,bj, vtype, indu, var, myThid ) |
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MNC_CW_RX_R_YY( fbname,bi,bj, vtype, indu, var, myThid ) |
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MNC_COMP_VTYPE_VAR( ind_vt, ind_fv_ids, ires, myThid ) |
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To-Do: |
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====== |
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1) NAMING -- We should (as much as possible) try to name variables so |
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that they are in agreement with the CF naming conventions. |
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2) UNITS -- as with the names we need to follow conventions |
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3) AM described her "diags" (or "myDiags" or "mDiags") interface |
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which should use MNC for output. The data storage idea is similar |
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to the MNC tables-of-indicies approach but also includes one huge |
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double-precision "accumulator" to hold all the temporary values |
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(eg. partial sums for averages, current max/mins): |
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vname ( ni ) |
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vlen ( ni ) |
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vind ( ni ) ------+ |
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| |
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vij_diag ( i, j, [...] ) w/ lat/lon indicies |
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vgl_diag ( [...] ) wo/ lat/lon indicies (global) |
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4) CNH pointed out that grid interpolation needs to be handled |
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"on-the-fly" since pre-processing would result in overly large |
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input files. We need an interpolation API... |
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5) From the group meeting on 2004/01/21, we need to define |
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"sub-grids" corresponding to: |
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var_name HGRID VGRID TIME |
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=========================================== |
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u U_xy r_c t |
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eta T_xy - t |
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rac T_xy - - |
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And write a convenience wrapper so that users can write variables |
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using just two function calls. JMC and I worked out the |
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following: |
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