v.plant(1)	       Grass User's Manual	       v.plant(1)



NNAAMMEE
       vv..ppllaanntt	 -  module to insert intermediate points on GRASS
       vector lines.
       _(_G_R_A_S_S _V_e_c_t_o_r _P_r_o_g_r_a_m_)

SSYYNNOOPPSSIISS
       vv..ppllaanntt
       vv..ppllaanntt hheellpp
       vv..ppllaanntt mmaapp==_n_a_m_e


       v.plant is an interactive program.



DDEESSCCRRIIPPTTIIOONN
       This report describes the use and operation of the program
       _v_._p_l_a_n_t,  used with the GRASS GIS system.  The report con-
       tains (i) a discussion of the problem which motivated  the
       development  of	the  program,  (ii)  a description of the
       method used, (iii) the manual page describing the usage of
       the program,  (iv) a listing of the source-code.

IInnttrroodduuccttiioonn
       _M_a_p _p_r_o_j_e_c_t_i_o_n_s

       Projections  are representations of information defined on
       curved surfaces	(usually  spheroids)  in  two-dimensional
       space.  This allows the description of the location infor-
       mation in cartesian or  other  plane  coordinate  systems.
       Particular projections are defined by precise mathematical
       relations, which allows conversion of  maps  from  between
       projections to be achieved using straightforward mathemat-
       ical operations [1].

       _P_r_o_j_e_c_t_i_n_g _l_i_n_e _s_e_g_m_e_n_t_s

       When  converted	from  one  map	projection  to	 another,
       straight-lines  become curves.  Thus, a line segment which
       can be described by four parameters only (eg  the  coordi-
       nates  of the end points) in one projection becomes an arc
       which needs more parameters in other projections.  In  GIS
       systems	which  describe  arcs  as a sequence of line seg-
       ments, this means that  intermediate  points  between  the
       ends  of the segment are used.  The easiest method of pro-
       jecting a  line	accurately  is	to  include  intermediate
       points  in  the	description  in the source projection, so
       that all these points are included in the target map.

       _C_o_n_t_e_x_t _w_i_t_h_i_n _t_h_e _G_R_A_S_S _G_I_S

       Vector maps (lines and arcs) in the GRASS GIS  are  repre-
       sented  by  a  relatively straightforward format.  This is
       exemplified in the ascii version of vector files, as  pro-
       duced by _v_._o_u_t_._a_s_c_i_i [2] and described in the programmer's
       manual [3].  Individual vector segments are described by a
       sequence  of  coordinate pairs, with the number of coordi-
       nated pairs for the segment recorded in a brief header for
       each  segment.	The  program  _v_._p_r_u_n_e  [4] is provided to
       remove points which are considered redundant through being
       too  close  together  within  a segment.  _v_._p_l_a_n_t has been
       designed as the complement of this, to insert extra points
       at a specified spacing along straight-line segments.

	DDeessiiggnn ooff vv..ppllaanntt

       _v_._p_l_a_n_t	has  been  implemented	as a Bourne shell script.
       The basic procedure is as follows:

       1.  Write out the existing map in the _d_i_g___a_s_c_i_i format;

       2.  Use an included _a_w_k script to process each vector seg-
       ment  in  turn,	moving from point to point along the seg-
       ment.  If a span between two adjacent  points  is  greater
       than  the  specified threshold (in map units) extra points
       are inserted collinearly.

       3.  The modified _d_i_g___a_s_c_i_i file is re-imported,	overwrit-
       ing the original file.

       Because the original _d_i_g file is overwritten, all the sup-
       port files  are	preserved.   Since  the  vector  segments
       remain  in  the same sequence, and all the original points
       remain in the modified map, including  the  end-points  of
       each  segment,  all  topology,  attributes,  etc are main-
       tained.

       The usage is exemplified in the attached manual page.  The
       source  code is also attached, which may be examined for a
       detailed understanding of the method.

TTOODDOO
       A command-line version of _v_._p_l_a_n_t would be  highly  desir-
       able.

SSEEEE AALLSSOO
       _v_._p_r_u_n_e _v_._s_u_p_p_o_r_t

RReeffeerreenncceess
       [1]  Evenden,  G.I.  (1990) Cartographic projection proce-
       dures for the UNIX environment - a  user's  manual.   USGS
       Open-File  Report  90-284 (Also see Interim Report and 2nd
       Interim Report on Release 4, Evenden 1994).

       [2]  Higgins, M. & Westervelt, J.  v.out.ascii -  Converts
       a binary GRASS vector map layer into an ASCII GRASS vector
       map layer.  GRASS 4.1 documentation (main section).

       [3]  Shapiro, M., Westervelt, J, Gerdes, D., Larson, M.	&
       Brownfeld, K.R.	(1993) GRASS 4.1 programmer's manual.  US
       Army Construction Engineering Research Laboratory.

       [4]  Gerdes D.,	v.prune - Prunes points from binary GRASS
       vector  data  files.   GRASS  4.1 documentation (main sec-
       tion).


       Copyright (C)  1997 AGCRC & CSIRO

       CSIRO Exploration & Mining Report 239F, March 1996.

       S.J.D. Cox

       _A_G_C_R_C_, _C_S_I_R_O _E_x_p_l_o_r_a_t_i_o_n _& _M_i_n_i_n_g_, _N_e_d_l_a_n_d_s_, _W_A

       _L_a_s_t _c_h_a_n_g_e_d_: _$_D_a_t_e_: _2_0_0_2_/_0_1_/_2_5 _0_5_:_4_5_:_3_5 _$



GRASS 5.0					       v.plant(1)
