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      This object is a wrapper for the CAT_ARROW routine in IDL. It provides a simple
      way to draw arrows or vectors on images which use a MAPCOORD object to set up the map
      projection space. A map coordinate space must be in effect at the time the
      Draw method of this object is used.


      David Fanning, Ph.D.
      1645 Sheely Drive
      Fort Collins, CO 80526 USA
      Phone: 970-221-0438
      E-mail: davidf@dfanning.com
      Coyote's Guide to IDL Programming: http://www.dfanning.com



Calling Sequence

      mapCoord = Obj_New('MapCoord', 111, CENTER_LON=0, CENTER_LAT=90)
      vectorObject = Obj_New('Map_Vector', lon, lat, u, v, mapCoord)
      vectorObject -> Draw
      ObjDestroy, mapCoord, vectorObject


      lon: A vector (or scalar) containing the longitude location of the (x0,y0) end of a vector.
      lat: A vector (or scalar) containing the latitude location of the (x0,y0) end of a vector.
      u: A vector (or scalar) containing the horizontal (X or longitude) component of the vector.
      v: A vector (or scalar) containing the vertical (Y or latitude) component of the vector.
      mapCoordObj: A map coordinate object which can return a map structure for converting coordinates
                      to/from lat/lon coordinates to XY coordinates. Typically, a MAPCOORD object. An
                      alternative way of specifying a map coordinate object is to use the MAP_OBJECT
                      keyword. But don't do both. Note, this object is *not* destroyed when the MAP_VECTOR
                      object is destroyed. You are responsible for destroying the map coordinate object.
                      A map coordinate object is REQUIRED. So, if you don't specify this parameter, use the
                      MAP_OBJECT keyword to pass this object into the program.


  All of the following INIT keywords can be set and obtained using the SETPROPERTY and GETPROPERTY methods.
      CLIP: The coordinates of a rectangle used to clip the graphics output.
                      The rectangle is specified as a vector of the form [X0, Y0, X1, Y1],
                      giving coordinates of the lower left and upper right corners,
                      respectively. The default clipping rectangle is the plot window set
                      up by the MAPCOORD object.
      COLOR: The name of the color to draw the arrow or vector in. Default: "white".
      HSIZE: The value of this keyword sets the length of the arrowhead. See the documenation
                      for the ARROW command for further explanation. Default is -0.35.
      LENGTH: The U and V vectors are mutiplied by LENGTH before they are used
                      to calculate the (x1,y1) endpoint of the vector. By default, the length is set
                      to 1/100th of the XRANGE of the MapCoord object. This means that the maximum
                      length of a vector will be approximately LENGTH * SQRT(2).
      LINESTYLE: Set this keyword to the type of linestyle desired. See Graphics Keywords in
                      the on-line help for additional information. Default is 0, solid line.
      MAP_OBJECT: A MAPCOORD object or equivalent which had the ability to provide a map
                      structure with a GetMapStructure method. Don't use this keyword if you have
                      passed a map coordinate object as a positional parameter.
      NOCLIP: Set this keyword to surpress clipping of the arrow. Set to 0 by default.
      PARENT: An object reference to an object that will be the parent of this object.
      SOLID: Set this keyword to make a solid arrow, using polygon fills.
      THICK: The thickness of the lines. Set to 1.0 by default.
      UVCOORDS: Set this keyword if the LON and LAT arrays are specified in UV coordinates, rather than
                      longitude and latitude coordinates.


      The following programs (at least) are required from the Coyote Library:

Modification History

      Written by David W. Fanning, 14 June 2010.

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