NAME

       MAPIT - Draws lines on a map.

SYNOPSIS

       CALL MAPIT (RLAT,RLON,IFST)

C-BINDING SYNOPSIS

       #include <ncarg/ncargC.h>

       void c_mapit (float rlat, float rlon, int ifst)

DESCRIPTION

       RLAT and RLON
                   (input  expressions, of type REAL) specify the latitude and longitude of a point to which the
                   "pen" is to be moved. Both are given  in  degrees.  RLAT  must  be  between  -90.  and  +90.,
                   inclusive; RLON must be between -540. and +540., inclusive.

       IFST        (an  input expression, of type INTEGER) is 0 to do a "pen-up" move, 1 to do a "pen-down" move
                   only if the distance from the last point to the new point is greater than 'MV' plotter units,
                   and 2 or greater to do a "pen-down" move regardless of the distance from the  last  point  to
                   the new one.

C-BINDING DESCRIPTION

       The C-binding argument descriptions are the same as the FORTRAN argument descriptions.

USAGE

       MAPIT  is used to draw lines on the map; it is called by EZMAP itself and, if desired, by the user. MAPIT
       attempts to omit nonvisible portions of lines and to handle "crossover," a jump from one end of  the  map
       to  the  other  caused  by  the  projection  of  the  globe  onto  a flat surface. Crossover can occur on
       cylindrical and conical projections; MAPIT handles it gracefully on the former and not  so  well  on  the
       latter.

       To  draw the projection of a line defined by a series of lat/lon coordinates, start by calling MAPIT with
       the coordinates of the first point and with IFST = 0.  Then, call MAPIT repeatedly with  the  coordinates
       of  the  next point along the line and with IFST = 1 or 2.  (IFST = 2 is normally used only for the final
       point, to ensure closure with a line drawn by another series of calls.)  Finally, if the next thing  your
       program does is stop, call FRAME, or change attributes like color or line width, you should call MAPIQ to
       flush MAPIT's buffers.

       The  EZMAP  parameter  'DL'  determines whether MAPIT draws solid lines or dotted lines. Dotted lines are
       drawn using calls to POINTS. Solid lines are drawn using calls to DASHD, FRSTD, and VECTD. The parameters
       'DD' and 'MV' also affect MAPIT's behavior. See the descriptions of these parameters in the  ezmap_params
       man page.

       Keep in mind the following:

       •   The  projection of the line segment joining two points on the globe is considered to be the straight-
           line segment joining the projections of the points; no attempt is made to project it as if it were  a
           portion of a great circle.

       •   If both endpoints of a line segment are visible, the segment is considered to be entirely visible.

       •   If both endpoints are invisible, the segment is considered to be entirely invisible.

       •   If  one endpoint is visible and the other is not, a new point is interpolated at the boundary between
           the visible and invisible portions.  Only visible portions of the line are drawn.

       Because of these considerations, points defining a line should not be too far apart on the globe.

       There are two types of boundaries between visible and invisible regions:

       •   The limb is a boundary between a projectable region  and  an  unprojectable  one.  The  limb  may  be
           circular,  elliptical,  or  some other shape, depending on the projection being used. For example, an
           orthographic projection has as its limb a circle, centered at (0,0), with a radius of 1.

       •   The perimeter is a rectangular or elliptical boundary defined by  EZMAP  parameters  set  by  you  to
           specify the region you wish to view.

EXAMPLES

       Use the ncargex command to see the following relevant examples: cmpgci, cmptra, mpexfi.

ACCESS

       To  use  MAPIT  or c_mapit, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in
       that order.

SEE ALSO

       Online: ezmap, ezmap_params, mapaci, mapbla, mapblm, mapdrw,  mapeod,  mapfst,  mapgci,  mapgrd,  mapgrm,
       mapgtc,  mapgti,  mapgtl,  mapgtr, mapint, mapiq, mapiqa, mapiqd, mapiqm, mapita, mapitd, mapitm, maplbl,
       maplmb, maplot, mappos, maproj, maprs, maprst, mapsav, mapset, mapstc, mapsti,  mapstl,  mapstr,  maptra,
       maptri,  maptrn,  mapusr, mapvec, mpchln, mpfnme, mpgetc, mpgeti, mpgetl, mpgetr, mpglty, mpiaty, mpifnb,
       mpilnb, mpiola, mpiosa, mpipai, mpipan, mpipar, mpisci, mplnam, mplndm, mplndr, mplnri,  mpname,  mprset,
       mpsetc, mpseti, mpsetl, mpsetr, supmap, supcon, ncarg_cbind

       Hardcopy: NCAR Graphics Contouring and Mapping Tutorial

COPYRIGHT

       Copyright (C) 1987-2009
       University Corporation for Atmospheric Research
       The use of this Software is governed by a License Agreement.

UNIX                                               March 1993                                      MAPIT(3NCARG)