r.fusion: lowres-highres image fusion (OSGeo#997)

* r.fusion: lowres-highres image fusion Co-authored-by: Anna Petrasova <kratochanna@gmail.com> --------- Co-authored-by: Anna Petrasova <kratochanna@gmail.com>
rohannallamadge · Jan 9, 2024 · e978f60 · e978f60
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diff --git a/src/raster/r.fusion/Makefile b/src/raster/r.fusion/Makefile
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+MODULE_TOPDIR = ../..
+
+PGM = r.fusion
+
+include $(MODULE_TOPDIR)/include/Make/Script.make
+
+default: script
diff --git a/src/raster/r.fusion/r.fusion.html b/src/raster/r.fusion/r.fusion.html
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+<h2>DESCRIPTION</h2>
+
+<em>r.fusion</em> enhances the resolution of a raster map by using spatial 
+detail of a high-resolution map. The actual values in the resultant output map 
+correspond to the input map while the spatial detail corresponds to the 
+high-resolution map. The effect is similar to pan-sharpening, but the method 
+can be applied more generally, not only to imagery but also to climatological 
+data such as temperature or precipitation.
+
+<h2>NOTES</h2>
+
+Two different methods are available with the <b>method</b> option: 
+<em>difference</em> and <em>proportion</em>.
+
+<p>
+The <em>difference</em> method uses the formula
+<p>
+A - B + B = A
+<p>
+more specifically
+<p>
+highres(A<sub>lowres</sub> - B<sub>lowres</sub>) + B<sub>highres</sub> = A<sub>highres</sub>
+<p>
+where <em>highres()</em> is a function to interpolate the differences. Here, 
+<em>r.resamp.filter</em> is used for interpolation.
+
+<p>
+The <em>proportion</em> method is suitable for e.g. precipitation where zero 
+precipition must stay zero precipition, and uses the formula
+<p>
+A / B * B = A
+<p>
+more specifically
+<p>
+highres(A<sub>lowres</sub> / B<sub>lowres</sub>) * B<sub>highres</sub> = A<sub>highres</sub>
+<p>
+
+Again, <em>highres()</em> is a function to interpolate the proportions, and 
+<em>r.resamp.filter</em> is used for interpolation. For the <em>proportion</em> 
+method, all values in the high-resolution B map must be &gt; 0.
+
+
+<h2>SEE ALSO</h2>
+
+<em>
+<a href="https://grass.osgeo.org/grass-stable/manuals/r.resamp.filter.html">r.resamp.filter</a>
+</em>
+
+
+<h2>AUTHOR</h2>
+
+Markus Metz, mundialis