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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.

Modification History

      Written by David W. Fanning, 14 June 2010.

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