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@@ -8,10 +8,10 @@ ground and the sun rays. It can be obtained with <em>r.sun</em>
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(parameter incidout), and then calculating its cosine with float precision.
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<p>
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-Using flag -i and given an elevation map as basemap (metric),
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-<em>i.topo.corr</em> permits to obtain a simple illumination model from the formula:
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+Using the <b>-i</b> flag and given an elevation basemap (metric),
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+<em>i.topo.corr</em> creates a simple illumination model using the formula:
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<ul>
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- <li> cos_i = cos(s) * cos(z) + sin(s) * sin(z) * cos(a - o) </li>
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+ <li> cos_i = cos(s) * cos(z) + sin(s) * sin(z) * cos(a - o) </li>
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</ul>
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where,
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<em>s</em> is the terrain slope angle, <em>z</em> is the solar zenith angle,
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@@ -26,13 +26,13 @@ the original reflectance (ref_o) using one of the four offered methods
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<h3>Method: cosine</h3>
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<ul>
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-<li> ref_c = ref_o * cos_z / cos_i </li>
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+ <li> ref_c = ref_o * cos_z / cos_i </li>
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</ul>
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<h3>Method: minnaert</h3>
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<ul>
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-<li>ref_c = ref_o * (cos_z / cos_i) ^k</li>
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+ <li>ref_c = ref_o * (cos_z / cos_i) ^k</li>
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</ul>
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where,
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<em>k</em> is obtained by linear regression of<br>
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@@ -41,7 +41,7 @@ ln(ref_o) = ln(ref_c) - k ln(cos_i/cos_z)
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<h3>Method: c-factor</h3>
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<ul>
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-<li>ref_c = ref_o * (cos_z + c)/ (cos_i + c)</li>
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+ <li>ref_c = ref_o * (cos_z + c)/ (cos_i + c)</li>
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</ul>
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where,
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<em>c</em> is a/m from ref_o = a + m * cos_i
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@@ -54,9 +54,10 @@ then the transformation (cos_i + 1)/2 varied from 0
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(direct exhibition to the sun: no correction) and the corrected reflectance can
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be calculated as
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<ul>
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-<li>ref_c = ref_o * 2 / (cos_i + 1)</li>
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+ <li>ref_c = ref_o * 2 / (cos_i + 1)</li>
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</ul>
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+
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<h2>NOTES</h2>
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<ol>
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@@ -67,6 +68,7 @@ be calculated as
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<li>The elevation map to calculate the illumination model should be metric.</li>
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</ol>
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+
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<h2>EXAMPLES</h2>
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First, make a illumination model from the elevation map (here, SRTM). Then
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@@ -81,6 +83,7 @@ i.topo.corr base=SRTM.illumination input=toar.5,toar.4,toar.3 out=tcor \
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zenith=33.3631 method=c-factor
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</pre></div>
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+
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<h2>REFERENCES</h2>
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<ul>
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@@ -109,6 +112,7 @@ i.topo.corr base=SRTM.illumination input=toar.5,toar.4,toar.3 out=tcor \
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<a href="r.sun.html">r.sun</a>
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</em>
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+
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<h2>AUTHOR</h2>
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E. Jorge Tizado (ej.tizado unileon es)<br>
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