New version of NCAR Graphics available!

From: Mary Haley (haley AT ucar.edu)
Date: Sun Dec 19 2004 - 20:25:14 MST

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    Dear NCAR Graphics users,

    We are very excited to announce the release of NCAR Graphics Version
    4.4.0!

    The most significant new capability in this release is a utility
    called CONPACKT ("CONtouring Package, Triangular"), which is a package
    of routines allowing one to deal with contours on an arbitrary surface
    in 3-space, as approximated by a triangular mesh.

    This version also contains a PDF driver, allowing one to output PDF
    files directly from an NCAR Graphics program (much in the same way
    direct PostScript output from an NCARG program works).

    For a full list of what's new in this version, and to see the latest
    documentation, please go to:

         http://ngwww.ucar.edu/ng/whatsnew.html#WhatsNew4_4_0
         http://ngwww.ucar.edu/ng/documentation.html

    NCAR Graphics V4.4.0 builds on just about any flavor of UNIX,
    including Linux, MacOSX, Solaris, IRIX, AIX, HPUX, OSF1, and Cygwin
    (under Windows).

    To download source code and/or some precompiled binaries, go to:

         http://ngwww.ucar.edu/ng/download.html

    This capability is also available in the NCAR Command Language (NCL),
    which can be downloaded in binary format from:

         http://ngwww.ucar.edu/ncl/download.html

    Since CONPACKT is the most significant new utility to be added in the
    last few years, we have included a detailed description below of its
    capability and usage.

    When the contouring package called CONPACK was written, most of the
    surface data that we saw was representable by a two-dimensional array.
    In the case of data on the surface of the earth, one of the array
    indices was identified with longitude and the other with latitude
    (which resulted in uneven coverage of the earth, with the rectangles
    at the poles turning into long, narrow triangles). For polar
    coordinate data (using "R" and "theta" coordinates), one of the
    indices was identified with "R" and the other with "theta". In some
    cases, a rectangular array could be made to represent an irregular
    shape in the plane by using auxiliary two-dimensional arrays to
    specify the positions of the mesh points there, but this technique was
    severely limited.

    In recent years, we have begun to see more and more examples of grids
    which, for one reason or another, cannot be handled by CONPACK. Some
    of these are still inherently rectangular in nature, but have features
    that cause the CONPACK algorithms to fail (for example, the ORCA grid,
    in which portions of a rectangular array wrapped around the globe are
    discontinuously moved with respect to the rest so as to provide
    higher-resolution coverage of certain areas). Others are not even
    rectangular in nature (like the geodesic grid and a variety of
    triangular meshes meant to represent regions having complex shapes,
    like the Chesapeake Bay). Those who use such grids usually prefer not
    to interpolate to a rectangular grid in order to contour their data
    (even in cases in which such interpolation is possible). So, we began
    looking for ways to draw contours more or less directly from as large
    a variety of different grids as possible. The result is CONPACKT.

    Every type of grid that we have seen so far (including the ones that
    CONPACK could handle) can be reduced to a triangular mesh, so we
    settled on that as the most basic structure to use. The mesh consists
    of: a list of points, defined by X, Y, and Z coordinates in 3-space; a
    list of edges, defined by pairs of points; and a list of triangles,
    defined by triplets of joined edges. The mesh must be simply
    connected: no two edges may intersect except at their end points and
    no edge may be a part of more than two triangles. To enable the
    tracing of contour lines on the mesh, pointers belonging to each edge
    tell one which triangles it is a part of.

    To make the process of constructing a triangular mesh as easy as
    possible, two different routines are provided. Also, a large number
    of examples are available, showing how to deal with various kinds of
    grids:

        - rectangular grids that are transformed to represent the surface
          of the earth, including simple lat/lon grids, Gaussian grids, POP
          grids, and ORCA grids;

        - the ISCCP grid, which is sort of rectangular on a cylindrical
          equidistant projection of the earth, but is not the sort of grid
          that CONPACK could handle;

        - intrinsically non-rectangular grids that represent the entire
          surface of the globe or a portion thereof, including geodesic
          grids and SEAM grids;

        - complicated triangular meshes representing portions of the globe
          having irregular shapes (including one representing Chesapeake
          Bay, another representing ocean areas off the coast of North
          Carolina, and a third representing the part of the Earth's
          surface seen by a satellite during a single orbit);

        - deformed rectangular meshes in a plane (including one
          representing a vertical slice through an ocean basin, deformed to
          follow the terrain of the ocean bottom);

        - triangular meshes representing an arbitrary surface in 3-space
          (like the surface of a lumpy asteroid or an isosurface of a
          magnetic field).

    The structure of CONPACKT and its internal parameters are very much
    like those of the existing package CONPACK, but there are some
    differences, as well:

        - Missing points on a rectangular grid are handled by CONPACK using
          a "special value" to mark areas in which contours are not to be
          drawn. CONPACKT has no such "special value", but it does allow
          one to "block" selected triangles, and, of course, one can just
          omit portions of the triangular mesh where contours are not to be
          drawn.

        - The routine CPCICA, in CONPACK, constructs a cell array in which
          the color of each cell is determined by the value of the contour
          field at the center of the cell; it depends on the ability of the
          mapping routine CPMPXY to do not only forward mappings from a
          position on the rectangular grid to a position on the plotter
          frame, but the inverse; this allows it to determine a color for
          every cell. The analogous routine CTCICA, in CONPACKT, cannot
          depend on the analogous mapping routine CTMXYZ to do inverse
          mappings and therefore works differently. Practically, what this
          means is that, if portions of the triangular mesh are invisible
          under the current mapping (for example, if they're on the "far
          side" of the globe), cells near the visible/invisible boundary
          may default to a background "cannot-determine-a-value" color.

    ----------------------------------------------------------------------

    I will add more precompiled binaries of NCAR Graphics V4.4.0 as
    time permits, so don't despair if you don't see your system
    in the download list yet.

    Cheers,

    --Mary Haley

    -------------------------------------------------
    Mary Haley haley@ucar.edu
    NCAR/SCD/VETS 303-497-1254 (voice)
    1850 Table Mesa Dr 303-497-1804 (fax)
    Boulder, CO 80305
    -------------------------------------------------

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