read_ncfield

'read_ncfield': reads one or two velocity fields and associated parameters from a file . 
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 COMBINE ET REMPLACE read_vel et read_scalar_new
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 OUTPUT:
 nb_coord,nb_dim,
 Civ: =0 or 1, indicates whether the data is civ (A SUPPRIMER ?)
 CivStage: =0, ??? A UTILISER POUR REMPLACER civ
           =1, civ1 has been performed only
           =2, fix1 has been performed
           =3, pacth1 has been performed
           =4, civ2 has been performed 
           =5, fix2 has been performed
           =6, pacth2 has been performed
 time: absolute time
 Field
            .Txt: (char string) error message if any
            .NbDim: number of dimensions (=0 by default)
            .NbCoord: number of vector components
            .CoordType: expresses the type of coordinate ('px' for image, 'sig' for instruments, or 'phys')
            .dt: time interval for the corresponding image pair
            .X, .Y, .Z: set of vector coordinates 
            .U,.V,.W: corresponding set of vector components
            .F: warning flags
            .FF: false flag, =0 for good vectors
            .C: scalar associated with velocity (used for vector colors)
            .CoordType
            .DijU; matrix of spatial derivatives (DijU(1,1,:)=DUDX,
            DijU(1,2,:)=DUDY, Dij(2,1,:)=DVDX, DijU(2,2,:)=DVDY
            .A, .AX, .AY: additional scalar
 dt:time interval of the image pair red from a single file, or vector with