[GRASSweb-list]markus: web/grass51/tutorial vectoroverlay.html,NONE,1.1 index.html,1.18,1.19

grass at intevation.de grass at intevation.de
Thu Aug 14 11:25:07 EDT 2003

Author: markus

Update of /grassrepository/web/grass51/tutorial
In directory doto:/tmp/cvs-serv28017

Modified Files:
Added Files:
Log Message:
vector overlay/clipping examples added

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   <title>GRASS 5.1: Vector overlay/clipping tutorial</title>

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GRASS 5.1: Vector overlay/clipping tutorial
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<a name="toc"></a>
<a href="index.html">Tutorial HOME</a> |
<a href="index.html#toc">Table of contents</a>

GRASS 5.1 is currently under development. It is neither complete (it still
contains only a few modules) nor it is intended for productional usage. 
Development releases are provided for people who want to help test, debug,
and improve GRASS 5.1. Knowing this, please read on.</i><br>
These examples described here may work or not. You are kindly invited to
send us further examples and/or code bugfixes/enhancements.</i>

<p><table width="100%" cellpadding="3" border="0">
<tr><td align="left" bgcolor="#B0F0B0"><font color="#00000"><big><b>
<a name="overlay"></a>
Some vector overlay/clipping examples
<DIV ALIGN=right><a href="#toc">[UP]</a></DIV>

To illustrate the GRASS vector overlay/clipping capabilities, we use data from VMAP 0, in particular the political
boundaries of Germany. The data set was extracted, reprojected to LatLong/WGS84 and converted to SHAPE 
with 'ogr2ogr'.
In a LatLong GRASS location we can do:
Import of this SHAPE file:
<div class="code"><pre>
v.in.ogr polbnda_germany.shp out=polbnda_germany
d.vect polbnda_germany

<a href=images/germany_latlong_with_polygon.png><DEFANGED_IMG src=images/germany_latlong_with_polygon_small.jpg alt="GRASS vector overlay/clipping example"></a>

Digitizing a triangle:
<div class="code"><pre>
v.digit -n clipmap
d.erase ; d.vect polbnda_germany col=blue
d.vect clipmap col=green

Vector union (AND):
<div class="code"><pre>
v.overlay ainput=polbnda_germany binput=clipmap output=clipmap_union operator=and -t
d.erase ; d.vect clipmap_union

<a href=images/clipmap_union.png><DEFANGED_IMG src=images/clipmap_union_small.jpg alt="GRASS vector overlay/clipping example"></a>

Vector intersection (OR):
<div class="code"><pre>
v.overlay ainput=polbnda_germany binput=clipmap output=clipmap_intersection operator=or -t
d.erase ; d.vect clipmap_intersection

<a href=images/clipmap_intersection.png><DEFANGED_IMG src=images/clipmap_intersection_small.jpg alt="GRASS vector overlay/clipping example"></a>

Vector cut out: features from polbnda_germany NOT in clipmap (NOT):
<div class="code"><pre>
v.overlay ainput=polbnda_germany binput=clipmap output=clipmap_not operator=not -t
d.erase ; d.vect clipmap_not

<a href=images/clipmap_not.png><DEFANGED_IMG src=images/clipmap_not_small.jpg alt="GRASS vector overlay/clipping example"></a>

Vector features from either polbnda_germany or clipmap but not those from
polbnda_germany overlayed by clipmap (XOR)
<div class="code"><pre>
v.overlay ainput=polbnda_germany binput=clipmap output=clipmap_xor operator=xor -t
d.erase ; d.vect clipmap_xor

<a href=images/clipmap_xor.png><DEFANGED_IMG src=images/clipmap_xor_small.jpg alt="GRASS vector overlay/clipping example"></a>

Further <a href=links.html>Links</a> (related software, SQL reference etc).

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<DIV ALIGN=right>&copy; 2003 Markus Neteler<br>
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<i>Last change:
$Date: 2003/08/14 15:25:05 $


Index: index.html
RCS file: /grassrepository/web/grass51/tutorial/index.html,v
retrieving revision 1.18
retrieving revision 1.19
diff -u -d -r1.18 -r1.19
--- index.html	13 Aug 2003 16:06:09 -0000	1.18
+++ index.html	14 Aug 2003 15:25:05 -0000	1.19
@@ -105,6 +105,8 @@
   <li><a href="network.html#vnetsteiner">v.net.steiner: optimized connection of nodes on a given vector network</a>
   <li><a href="network.html#vnetsalesman">v.net.salesman</a>
+ <li><a href="vectoroverlay.html">Vector overlay/clipping examples</a>
 <li><a href="troubleshooting.html">Troubleshooting</a>

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