imageryintro.html: add section about semantic labels (#2091)

* imageryintro.html: add section about semantic labels
* mention signature files
* imageryintro.html: semantic labels figure added. Source: https://trac.osgeo.org/grass/wiki/Grass8/NewFeatures80 --> https://trac.osgeo.org/grass/attachment/wiki/Grass8/NewFeatures80/band_references_scheme.png
* lib/imagery/Makefile: install PNG file(s)

Co-authored-by: Veronica Andreo <veroandreo@gmail.com>
Co-authored-by: Maris Nartiss <maris.gis@gmail.com>

imagery/imageryintro.html

@@ -86,6 +86,30 @@ an appropriate raster format (e.g. tiff, jpeg, png, pbm) and then use
 reference points the scanned map can be rectified to obtain geocoded
 data.
 
+<h3>Semantic label information</h3>
+
+Semantic labels are a description which can be stored as metadata.
+To print available semantic labels relevant for multispectral satellite
+data, use <a href="i.band.library.html">i.band.library</a>.
+<a href="r.semantic.label.html">r.semantic.label</a> allows assigning of
+these satellite imagery band references as defined in
+<a href="i.band.library.html">i.band.library</a>. Semantic labels are
+also used in signature files of imagery classification tools. Therefore, 
+signature files of one imagery or raster group can be used to classify
+a different group with identical semantic labels.
+
+<div align="center" style="margin: 10px">
+<img src="band_references_scheme.png" width=600 height=435 border=0><br>
+<i>
+    New enhanced classification workflow involving semantic labels.
+</i>
+</div>
+
+With <a href="r.support.html">r.support</a> any sort of semantic label
+the user wishes may be added (i.e., not only those registered in 
+<em>i.band.library</em>). Semantic labels are supported also by the
+<a href="temporalintro.html">temporal</a> GRASS modules.
+
 <h3>Image processing operations</h3>
 
 GRASS raster/imagery map processing is always performed in the current

lib/imagery/Makefile

@@ -7,9 +7,13 @@ EXTRA_CFLAGS = $(VECT_CFLAGS)
 
 include $(MODULE_TOPDIR)/include/Make/Lib.make
 include $(MODULE_TOPDIR)/include/Make/Doxygen.make
+include $(MODULE_TOPDIR)/include/Make/Grass.make
 
+# images
+IMGSRC := $(wildcard *.png) $(wildcard *.jpg) $(wildcard *.gif)
+IMGDST := $(patsubst %,$(HTMLDIR)/%,$(IMGSRC))
 
-default: lib
+default: $(IMGDST) lib
 
 #doxygen:
 DOXNAME=imagery