r.in.lidar: update man page

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@61918 15284696-431f-4ddb-bdfa-cd5b030d7da7

raster/r.in.lidar/r.in.lidar.html

@@ -89,9 +89,14 @@ A LiDAR pulse can have multiple returns. The first return values can be
 used to obtain a digital surface model (DSM) where e.g. canopy cover is 
 represented. The last return values can be used to obtain a digital 
 terrain model (DTM) where e.g. the forest floor instead of canopy 
-cover is represented. The <b>filter</b> option allows to select one of 
+cover is represented. The <b>return_filter</b> option allows to select one of 
 first, mid, or last returns.
 <p>
+LiDAR points can be already classified into standardized classes. For example,
+class number 2 represents ground (for other classes see LAS format specification
+in references). The <b>class_filter</b> option allows to select one or more 
+classes, as numbers (integers) separated by comma.
+<p>
 The default map <b>type</b>=<tt>FCELL</tt> is intended as compromise between
 preserving data precision and limiting system resource consumption.
 
@@ -280,6 +285,13 @@ Development Team.
 <a href="v.surf.bspline.html">v.surf.bspline</a>
 </em>
 
+<h2>REFERENCES</h2>
+
+<a href="http://www.asprs.org/Committee-General/LASer-LAS-File-Format-Exchange-Activities.html">
+ASPRS LAS format</a><br>
+<a href="http://www.liblas.org/">LAS library</a> <br>
+<a href="http://test.liblas.org/doxygen/liblas_8h.htm">LAS library C API</a> documentation
+
 <h2>AUTHORS</h2>
 
 Markus Metz<br>