mapproject              package:mapproj              R Documentation

_A_p_p_l_y _a _M_a_p _P_r_o_j_e_c_t_i_o_n

_D_e_s_c_r_i_p_t_i_o_n:

     Converts latitude and longitude into projected coordinates.

_U_s_a_g_e:

     mapproject(x, y, projection="", parameters=NULL, orientation=NULL)

_A_r_g_u_m_e_n_t_s:

     x,y: two vectors giving longitude and latitude coordinates of
          points on the earth's surface to be projected. A list
          containing components named 'x' and 'y', giving the
          coordinates of the points to be projected may also be given.
          Missing values ('NA's) are allowed. The coordinate system is
          degrees of longitude east of Greenwich (so the USA is bounded
          by negative longitudes) and degrees north of the equator. 

projection: optional character string that names a map projection to
          use. See below for a description of this and the next two
          arguments. 

parameters: optional numeric vector of parameters for use with the
          'projection' argument. This argument is optional only in the
          sense that certain projections do not require additional
          parameters. If a projection does require additional
          parameters, these must be given in the 'parameters' argument. 

orientation: An optional vector 'c(latitude,longitude,rotation)' which
          describes where the "North Pole" should be when computing the
          projection. This is mainly used for specifying the point of
          tangency for a planar projection; you should not use it for
          cylindrical or conic projections. The third value is a
          clockwise rotation (in degrees). 

_D_e_t_a_i_l_s:

     Each standard projection is displayed with the Prime Meridian
     (longitude 0) being a straight vertical line, along which North is
     up. The orientation of nonstandard projections is specified by the
     three 'parameters=c(lat,lon,rot)'. Imagine a transparent gridded
     sphere around the globe. First turn the overlay about the North
     Pole so that the Prime Meridian (longitude 0) of the overlay
     coincides with meridian 'lon' on the globe. Then tilt the North
     Pole of the overlay along its Prime Meridian to latitude 'lat' on
     the globe. Finally again turn the overlay about its "North Pole"
     so that its Prime Meridian coincides with the previous position of
     (the overlay) meridian 'rot'. Project the desired map in the
     standard form appropriate to the overlay, but presenting
     information from the underlying globe.

     In the descriptions that follow (adapted from the McIlroy
     reference), each projection is shown as a function call; if it
     requires parameters, these are shown as arguments to the function.
     The descriptions are grouped into families.

     Equatorial projections centered on the Prime Meridian (longitude
     0). Parallels are straight horizontal lines.

     _m_e_r_c_a_t_o_r() equally spaced straight meridians, conformal, straight
          compass courses

     _s_i_n_u_s_o_i_d_a_l() equally spaced parallels, equal-area, same as
          'bonne(0)'

     _c_y_l_e_q_u_a_l_a_r_e_a(_l_a_t_0) equally spaced straight meridians, equal-area,
          true scale on 'lat0'

     _c_y_l_i_n_d_r_i_c_a_l() central projection on tangent cylinder

     _r_e_c_t_a_n_g_u_l_a_r(_l_a_t_0) equally spaced parallels, equally spaced
          straight meridians, true scale on 'lat0'

     _g_a_l_l(_l_a_t_0) parallels spaced stereographically on prime meridian,
          equally spaced straight meridians, true scale on 'lat0'

     _m_o_l_l_w_e_i_d_e() (homalographic) equal-area, hemisphere is a circle

     _g_i_l_b_e_r_t() sphere conformally mapped on hemisphere and viewed
          orthographically

     Azimuthal projections centered on the North Pole. Parallels are
     concentric circles. Meridians are equally spaced radial lines.

     _a_z_e_q_u_i_d_i_s_t_a_n_t() equally spaced parallels, true distances from pole

     _a_z_e_q_u_a_l_a_r_e_a() equal-area

     _g_n_o_m_o_n_i_c() central projection on tangent plane, straight great
          circles

     _p_e_r_s_p_e_c_t_i_v_e(_d_i_s_t) viewed along earth's axis 'dist' earth radii
          from center of earth

     _o_r_t_h_o_g_r_a_p_h_i_c() viewed from infinity

     _s_t_e_r_e_o_g_r_a_p_h_i_c() conformal, projected from opposite pole

     _l_a_u_e() 'radius = tan(2 * colatitude)' used in xray crystallography

     _f_i_s_h_e_y_e(_n) stereographic seen through medium with refractive index
          'n'

     _n_e_w_y_o_r_k_e_r(_r) 'radius = log(colatitude/r)' map from viewing
          pedestal of radius 'r' degrees

     Polar conic projections symmetric about the Prime Meridian.
     Parallels are segments of concentric circles. Except in the Bonne
     projection, meridians are equally spaced radial lines orthogonal
     to the parallels.

     _c_o_n_i_c(_l_a_t_0) central projection on cone tangent at 'lat0'

     _s_i_m_p_l_e_c_o_n_i_c(_l_a_t_0,_l_a_t_1) equally spaced parallels, true scale on
          'lat0' and 'lat1'

     _l_a_m_b_e_r_t(_l_a_t_0,_l_a_t_1) conformal, true scale on 'lat0' and 'lat1'

     _a_l_b_e_r_s(_l_a_t_0,_l_a_t_1) equal-area, true scale on 'lat0' and 'lat1'

     _b_o_n_n_e(_l_a_t_0) equally spaced parallels, equal-area, parallel 'lat0'
          developed from tangent cone

     Projections with bilateral symmetry about the Prime Meridian and
     the equator. 

     _p_o_l_y_c_o_n_i_c() parallels developed from tangent cones, equally spaced
          along Prime Meridian

     _a_i_t_o_f_f() equal-area projection of globe onto 2-to-1 ellipse, based
          on 'azequalarea'

     _l_a_g_r_a_n_g_e() conformal, maps whole sphere into a circle

     _b_i_c_e_n_t_r_i_c(_l_o_n_0) points plotted at true azimuth from two centers on
          the equator at longitudes '+lon0' and '-lon0', great circles
          are  straight lines (a stretched gnomonic projection)

     _e_l_l_i_p_t_i_c(_l_o_n_0) points are     plotted at true distance from two
          centers on the equator at longitudes '+lon0' and '-lon0'

     _g_l_o_b_u_l_a_r() hemisphere is circle, circular arc meridians equally
          spaced on equator, circular arc parallels equally spaced on
          0- and 90-degree meridians

     _v_a_n_d_e_r_g_r_i_n_t_e_n() sphere is circle, meridians as       in
          'globular', circular arc parallels resemble 'mercator'

     _e_i_s_e_n_l_o_h_r() conformal with no singularities, shaped like polyconic

     Doubly periodic conformal projections.

     _g_u_y_o_u W and E hemispheres are square

     _s_q_u_a_r_e world is square with Poles at diagonally opposite corners

     _t_e_t_r_a map on tetrahedron with edge tangent to Prime Meridian at S
          Pole, unfolded into equilateral triangle

     _h_e_x world is hexagon centered on N Pole, N and S hemispheres are
          equilateral triangles

     Miscellaneous projections.

     _h_a_r_r_i_s_o_n(_d_i_s_t,_a_n_g_l_e) oblique    perspective from above the North
          Pole, 'dist' earth radii from center of earth, looking along
          the Date Line 'angle' degrees off vertical

     _t_r_a_p_e_z_o_i_d_a_l(_l_a_t_0,_l_a_t_1) equally spaced parallels, straight
          meridians equally spaced along parallels, true scale at
          'lat0' and 'lat1' on Prime Meridian

     _l_u_n_e(_l_a_t,_a_n_g_l_e) conformal, polar cap above latitude 'lat' maps to
          convex lune with given 'angle' at 90E and 90W

     Retroazimuthal projections. At every point the angle between
     vertical and a straight line to "Mecca", latitude 'lat0' on the
     prime meridian,   is the true bearing of Mecca. 

     _m_e_c_c_a(_l_a_t_0) equally spaced vertical meridians

     _h_o_m_i_n_g(_l_a_t_0) distances to Mecca are true

     Maps based on the spheroid. Of geodetic quality, these projections
     do not make sense for tilted orientations. 

     _s_p__m_e_r_c_a_t_o_r() Mercator on the spheroid.

     _s_p__a_l_b_e_r_s(_l_a_t_0,_l_a_t_1) Albers on the spheroid.

_V_a_l_u_e:

     list with components named 'x' and 'y', containing the projected
     coordinates. 'NA's project to 'NA's. Points deemed unprojectable
     (such as north of 80 degrees latitude in the Mercator projection)
     are returned as 'NA'. Because of the ambiguity of the first two
     arguments, the other arguments must be given by name.

     Each time 'mapproject' is called, it leaves on frame 0 the dataset
     '.Last.projection', which is a list with components 'projection',
     'parameters', and 'orientation' giving the arguments from the call
     to 'mapproject' or as constructed (for 'orientation'). Subsequent
     calls to 'mapproject' will get missing information from
     '.Last.projection'. Since 'map' uses 'mapproject' to do its
     projections, calls to 'mapproject' after a call to 'map' need not
     supply any arguments other than the data.

_R_e_f_e_r_e_n_c_e_s:

     Richard A. Becker, and Allan R. Wilks, "Maps in S", _AT&T Bell
     Laboratories Statistics Research Report, 1991._ <URL:
     http://www.research.att.com/areas/stat/doc/93.2.ps>

     M. D. McIlroy, documentation for from _Tenth Edition UNIX Manual,
     Volume 1,_ Saunders College Publishing, 1990.

     M. D. McIlroy,  Source code for maps and map projections. <URL:
     http://www.cs.dartmouth.edu/~doug/source.html>

_E_x_a_m_p_l_e_s:

     library(maps)
     # Bonne equal-area projection with state abbreviations
     map("state",proj='bonne', param=45)
     data(state)
     text(mapproject(state.center), state.abb)

     map("state",proj="albers",par=c(30,40))
     map("state",par=c(20,50)) # another Albers projection

     map("world",proj="gnomonic",orient=c(0,-100,0)) # example of orient
     # see map.grid for more examples

