note added for band7 and band7 naming (#73)

imagery/i.vi/i.vi.html

@@ -353,10 +353,12 @@ <h3>Calculation of GEMI</h3>
 
 <h3>Calculation of GVI</h3>
 
-The calculation of GVI from the reflectance values is done as follows:
+The calculation of GVI (Green Vegetation Index - Tasseled Cap) from the
+reflectance values is done as follows:
 
 <div class="code"><pre>
 g.region raster=band.3 -p
+# assuming Landsat-7
 i.vi blue=band.1 green=band.2 red=band.3 nir=band.4 band5=band.5 band7=band.7 viname=gvi output=gvi
 r.univar -e gvi
 </pre></div>

imagery/i.vi/main.c

@@ -161,6 +161,7 @@ int main(int argc, char *argv[])
     opt.blue->description = _("Range: [0.0;1.0]");
     opt.blue->guisection = _("Optional inputs");
 
+    /* TODO: the naming is suboptimal as specific to Landsat-7 */
     opt.chan5 = G_define_standard_option(G_OPT_R_INPUT);
     opt.chan5->key = "band5";
     opt.chan5->required = NO;
@@ -169,6 +170,7 @@ int main(int argc, char *argv[])
     opt.chan5->description = _("Range: [0.0;1.0]");
     opt.chan5->guisection = _("Optional inputs");
 
+    /* TODO: the naming is suboptimal as specific to Landsat-7 */
     opt.chan7 = G_define_standard_option(G_OPT_R_INPUT);
     opt.chan7->key = "band7";
     opt.chan7->required = NO;