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<h2>NAME</h2>
<em><b>v.lrs.create</b></em> - Create Linear Reference System
<h2>KEYWORDS</h2>
vector, LRS, networking
<h2>SYNOPSIS</h2>
<b>v.lrs.create</b><br>
<b>v.lrs.create help</b><br>
<b>v.lrs.create</b> <b>in_lines</b>=<em>name</em> <b>out_lines</b>=<em>name</em> [<b>err</b>=<em>name</em>] <b>points</b>=<em>name</em> [<b>llayer</b>=<em>integer</em>] [<b>player</b>=<em>integer</em>] <b>lidcol</b>=<em>string</em> <b>pidcol</b>=<em>string</em> [<b>start_mp</b>=<em>string</em>] [<b>start_off</b>=<em>string</em>] [<b>end_mp</b>=<em>string</em>] [<b>end_off</b>=<em>string</em>] <b>rstable</b>=<em>string</em> [<b>thresh</b>=<em>float</em>] [--<b>overwrite</b>] [--<b>verbose</b>] [--<b>quiet</b>]
<h3>Flags:</h3>
<DL>
<DT><b>--overwrite</b></DT>
<DD>Allow output files to overwrite existing files</DD>
<DT><b>--verbose</b></DT>
<DD>Verbose module output</DD>
<DT><b>--quiet</b></DT>
<DD>Quiet module output</DD>
</DL>
<h3>Parameters:</h3>
<DL>
<DT><b>in_lines</b>=<em>name</em></DT>
<DD>Input vector map containing lines</DD>
<DT><b>out_lines</b>=<em>name</em></DT>
<DD>Output vector map where oriented lines are written</DD>
<DT><b>err</b>=<em>name</em></DT>
<DD>Output vector map of errors</DD>
<DT><b>points</b>=<em>name</em></DT>
<DD>Input vector map containing reference points</DD>
<DT><b>llayer</b>=<em>integer</em></DT>
<DD>Layer number</DD>
<DD>Line layer</DD>
<DD>Default: <em>1</em></DD>
<DT><b>player</b>=<em>integer</em></DT>
<DD>Layer number</DD>
<DD>Point layer</DD>
<DD>Default: <em>1</em></DD>
<DT><b>lidcol</b>=<em>string</em></DT>
<DD>Column containing line identifiers for lines</DD>
<DT><b>pidcol</b>=<em>string</em></DT>
<DD>Column containing line identifiers for points</DD>
<DT><b>start_mp</b>=<em>string</em></DT>
<DD>Column containing milepost position for the beginning of next segment</DD>
<DD>Default: <em>start_mp</em></DD>
<DT><b>start_off</b>=<em>string</em></DT>
<DD>Column containing offset from milepost for the beginning of next segment</DD>
<DD>Default: <em>start_off</em></DD>
<DT><b>end_mp</b>=<em>string</em></DT>
<DD>Column containing milepost position for the end of previous segment</DD>
<DD>Default: <em>end_mp</em></DD>
<DT><b>end_off</b>=<em>string</em></DT>
<DD>Column containing offset from milepost for the end of previous segment</DD>
<DD>Default: <em>end_off</em></DD>
<DT><b>rstable</b>=<em>string</em></DT>
<DD>Name of table where the reference system will be written</DD>
<DD>New table is created by this module</DD>
<DT><b>thresh</b>=<em>float</em></DT>
<DD>Maximum distance of point to line allowed</DD>
<DD>Default: <em>1</em></DD>
</DL>
<h2>DESCRIPTION</h2>
<em>v.lrs.create</em> generates a LRS (Linear Reference System) from
vector line and point data.
<p>
It is highly recommended to work with polylines instead of segmented vector
lines. The command <em>v.build.polylines</em> creates this map structure.
<h2>NOTES</h2>
The mileposts (point) vector map columns <em>start_mp</em>, <em>start_off</em>,
<em>end_mp</em>, <em>end_off</em> must be of 'double precision' type. For
milepost ordering, it is sufficient to enter increasing numbers into the
<em>start_mp</em> column indicating the order along the vector line.
<p>
The <em>lidcol</em> and <em>pidcol</em> columns contain the line IDs which
relate mileposts and vector line(s) to each other.
<p>
When creating a LRS with this module, any existing <em>rstable</em> will be
replaced.
<h2>EXAMPLE</h2>
This example is written for the Spearfish dataset.
<p>
As first step, bus route data are prepared.
<div class="code"><pre>
# break into segments for correct route selection
v.clean roads_net out=busroute_tmp tool=break
# make polyline for easier line selection by coordinate pairs
v.build.polylines busroute_tmp out=busroute_tmp2
# reverse delete: reduce route map to bus route (enter in one line)
v.edit -r busroute_tmp2 tool=delete coords=590273,4927304,\
590346,4927246,590414,4927210,590438,4927096,590468,4926966,\
590491,4926848,590566,4926798,590637,4926753,590701,4926698,\
590830,4926726,590935,4926751,590993,4926830,590972,4926949,\
590948,4927066,590922,4927182,590957,4927251 thresh=5
# vector line needs to be polyline
v.build.polylines busroute_tmp2 out=busroute_tmp3
v.category busroute_tmp3 out=busroute op=add
g.remove vect=busroute_tmp,busroute_tmp2,busroute_tmp3
</pre></div>
The result can be visualized:
<div class="code"><pre>
g.region vect=busroute n=n+100 s=s-100 w=w-100 e=e+100
d.mon x0
d.vect roads_net
d.vect busroute col=red width=2
</pre></div>
The vector map 'busroute' needs have an attribute table which contain an integer column
<em>lidcol</em> with value be '22' for this example (bus route):
<div class="code"><pre>
v.db.addtable busroute col="lid integer"
v.db.update busroute col=lid value=22
v.db.select busroute
cat|lid
1|22
</pre></div>
A new point map 'busstops' shall contain mileposts (bus stops) along
this line (use <em>thresh</em> to define maximal accepted deviation from this line):
<div class="code"><pre>
# generate points map
echo "590263|4927361
590432|4927120
590505|4926776
590660|4926687
590905|4926742
590972|4926949
591019|4927263" | v.in.ascii out=busstops
d.vect busstops icon=basic/triangle col=blue
d.vect busstops disp=cat lcol=blue
</pre></div>
The milepost attributes table needs to be created with specific columns:
<div class="code"><pre>
v.db.addtable busstops col="lid integer, start_mp double precision, \
start_off double precision, end_mp double precision, \
end_off double precision"
v.db.update busstops col=lid value=22
</pre></div>
Since the digitizing order of v.in.ascii above reflects the bus stop
order along the route, we can simply copy the category number as milepost
order number in column <em>start_mp</em>:
<div class="code"><pre>
v.db.update busstops col=start_mp qcol=cat
# verify table
v.db.select busstops
cat|lid|start_mp|start_off|end_mp|end_off
1|22|1|||
2|22|2|||
3|22|3|||
4|22|4|||
5|22|5|||
6|22|6|||
7|22|7|||
# visualize with start_mp to check order
d.erase
d.vect roads_net
d.vect busroute col=red width=2
d.vect busstops icon=basic/triangle col=blue
d.vect busstops disp=attr attrcol=start_mp lcol=blue
</pre></div>
Offsets (<em>start_off</em>, <em>end_off</em>) can be later used in case the route or
mileposts get modified.
<p>
As second step, the linear reference network is created:
<div class="code"><pre>
v.lrs.create busroute points=busstops out=route_lrs err=lrs_error \
lidcol=lid pidcol=lid rstable=route_lrs thresh=50
</pre></div>
This creates the maps 'route_lrs' containing the LRS and 'lrs_error'
containing the errors if any. The resulting LRS table and map can
be shown:
<div class="code"><pre>
# show LRS table
db.select route_lrs
d.vect route_lrs col=blue width=2
</pre></div>
<h2>SEE ALSO</h2>
<em><a HREF="lrs.html">LRS tutorial</a></em>,<br>
<em><a HREF="http://gisws.media.osaka-cu.ac.jp/grass04/viewpaper.php?id=50">Introducing the Linear Reference System in GRASS</a></em>,
<p>
<em><a HREF="v.build.polylines.html">v.build.polylines</a></em>,
<em><a HREF="v.lrs.segment.html">v.lrs.segment</a></em>,
<em><a HREF="v.lrs.where.html">v.lrs.where</a></em>,
<em><a HREF="v.lrs.label.html">v.lrs.label</a></em>
<h2>AUTHOR</h2>
Radim Blazek, ITC-irst/MPA Solutions<br>
Documentation update (based on above journal article and available fragments): Markus Neteler
<p><i>Last changed: $Date: 2007-06-28 17:28:50 +0200 (Thu, 28 Jun 2007) $</i>
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