ZOOM                                                                       ZOOM



     The ZOOM command is summarized as follows:

          ZOOM is a data display command that allows the user to magnify a
          portion of the display window specified by the WINDOW command.  The
          user should display a map on the screen for orientation.  The area
          to be magnified is indicated by pointing to two diagonal corners of
          a rectangle that bound the new area of interest.  Pointing is accom-
          plished with the CRT crosshair cursor.  Effect of ZOOM can be re-
          versed with the RESET command.  If the GEOG option is used, the user
          may type in a geographic coordinate pair and set the display window
          with the coordinate pair as the center.  In addition, if the POINT
          option is used, the user may set the magnification factor and locate
          a point at the center of the area to be enlarged.


     The ZOOM command is specified as follows:
     (* denotes parameters which can only be entered in a prompted mode)

          ZOOM (crosshair input)*

          or,

          ZOOM GEOG (latitude)* (longitude)* (window size)*

          or,

          ZOOM POINT (magnification factor)* (crosshair input)*


     The individual parameters of the ZOOM command are described below:

          (crosshair input) is where the user points with the CRT cursor to
          the opposite diagonal corners of the new viewing rectangle.  This
          parameter is not used if the GEOG option is specified.

          GEOG is an option where the user is prompted to type in a geographic
          coordinate pair which is the center of a viewing window also set by
          the user.  This parameter may only be added in an un-prompted mode.

     The following parameters are prompted for if the GEOG option is specified:

          (latitude) and (longitude) are the coordinates of the a geographic
          pair used as the center of the window. Each will be prompted for
          seperately and should be entered in degrees, minutes and seconds.

          (window size) is the height and width of the window entered in
          seconds of latitude and longitude.

          POINT is an option where the user is prompted for a magnification
          factor and to point to the center of the area to be magnified.  This
          parameter may only be added in an un-prompted mode.

     The following parameter is prompted for if the POINT option is specified:

          (magnification factor) is used to indicate the change in scale. For
          example, if 2 is entered and the map is replotted, the features on the
          resulting map will be shown twice as large.

     The following are examples of use of the ZOOM commands:

         ENTER COMMAND
        ? ZOOM
         POINT TO CORNERS OF NEW DISPLAY WINDOW

       or,

         ENTER COMMAND
        ? ZOOM GEOG
         ENTER LATITUDE TO ZOOM ON
        ? 39 56 8
         ENTER LONGITUDE TO ZOOM ON
         -108 24 43
         ENTER SECONDS OF LONGITUDE AND LATITUDE FOR WINDOW
        ? 180 180

        or,

         ENTER COMMAND
        ? ZOOM POINT
         please enter MAGNIFICATION factor
        ? 2
         please point to ZOOM center



     The limitations of the ZOOM command are as follows:

          -- Cannot zoom to infinity, i.e., a point.

          -- Cannot point outside of the viewing window, i.e., cannot use ZOOM
             to enlarge the viewing window.
