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.