Geografic-Information-System/lib/vector/vectorascii.html

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A vector map in GRASS native vector format may contain a mix of
<i>primitives</i> including points, lines, boundaries, centroids, areas,
faces, and kernels. The GRASS ASCII vector format may contain also 
a <i>header</i> with various metadata (see example below).

<p>The header is similar as the head file of vector binary format but
contains bounding box also. Key words are:

<div class="code"><pre>
ORGANIZATION
DIGIT DATE
DIGIT NAME
MAP NAME
MAP DATE
MAP SCALE
OTHER INFO
ZONE
WEST EDGE
EAST EDGE
SOUTH EDGE
NORTH EDGE
MAP THRESH
</pre></div>

<p>The body begins with the row:

<div class="code"><pre>
VERTI:
</pre></div>

followed by records of primitives:

<div class="code"><pre>
TYPE NUMBER_OF_COORDINATES [NUMBER_OF_CATEGORIES]
 X Y [Z]
....
 X Y [Z]
[ LAYER CATEGORY]
....
[ LAYER CATEGORY]
</pre></div>

Everything above in <tt>[&nbsp;]</tt> is optional. 

<p>The primitive codes are as follows:
<ul>
  <li>'P': point</li>
  <li>'L': line</li>
  <li>'B': boundary</li>
  <li>'C': centroid</li>
  <li>'F': face (3D boundary)</li>
  <li>'K': kernel (3D centroid)</li>
  <li>'A': area (boundary) - better use 'B'; kept only for backward compatibility</li>
</ul>

The coordinates are listed following the initial line containing the
primitive code, the total number of coordinates in the series, and
(optionally) the number of categories (1 for a single layer, higher
for multiple layers).  Below that 1 or several lines follow to
indicate the layer number and the category number (ID).

<p>The order of coordinates is
<div class="code"><pre>
X Y [Z]
</pre></div>

In pre-GRASS 6 versions of the ASCII format, the order of coordinates
was different:
<div class="code"><pre>
Y X
</pre></div>

<p>Latitude/Longitude data may be given in a number of ways.
Decimal degrees must be positive or negative instead of using a hemisphere
letter. Mixed coordinates must use a hemisphere letter. Whole minutes and
seconds must always contain two digits (example: use <tt>167:03:04.567</tt>;
and not <tt>167:3:4.567</tt>). 
<br><br>
Acceptable formats:<br>
<i>key: D=Degrees; M=Minutes; S=Seconds; h=Hemisphere (N,S,E,W)</i>
<ul>
  <li><tt>(+/-)DDD.DDDDD</tt>
  <li><tt>DDDh</tt>
  <li><tt>DDD:MMh</tt>
  <li><tt>DDD:MM.MMMMMh</tt>
  <li><tt>DDD:MM:SSh</tt>
  <li><tt>DDD:MM:SS.SSSSSh</tt>
</ul>

<h2>EXAMPLES</h2>

<div class="code"><pre>
ORGANIZATION: GRASS Development Team
DIGIT DATE:   1/9/2005
DIGIT NAME:   -
MAP NAME:     test
MAP DATE:     2005
MAP SCALE:    10000
OTHER INFO:   Test polygons
ZONE:  0
MAP THRESH:   0.500000
VERTI:
B  6
 5958812.48844435 3400828.84221011
 5958957.29887089 3400877.11235229
 5959021.65906046 3400930.7458436
 5959048.47580612 3400973.65263665
 5959069.92920264 3401032.64947709
 5958812.48844435 3400828.84221011
C  1 1
 5958952.42189184 3400918.23126419
 1 20
B  4
 5959010.9323622 3401338.36037757
 5959096.7459483 3401370.54047235
 5959091.38259917 3401450.99070932
 5959010.9323622 3401338.36037757
C  1 1
 5959063.08352122 3401386.98533277
 1 21
</pre></div>

In this case the vector map contains 2 boundaries (first boundary with
6 vertices, second with 4 vertices) without category and 2 centroids
with category number 20 and 21 (layer 1).

<h2>SEE ALSO</h2>

<em>
  <a href="v.in.ascii.html">v.in.ascii</a>,
  <a href="v.out.ascii.html">v.out.ascii</a>,
  <a href="v.edit.html">v.edit</a>
</em>