http://dbbd.sg/wiki/index.php?action=history&feed=atom&title=ViewshedViewshed - Revision history2026-07-30T17:16:40ZRevision history for this page on the wikiMediaWiki 1.27.4http://dbbd.sg/wiki/index.php?title=Viewshed&diff=4661&oldid=prevWikiSysop at 06:05, 10 September 20092009-09-10T06:05:20Z<p></p>
<table class="diff diff-contentalign-left" data-mw="interface">
<col class='diff-marker' />
<col class='diff-content' />
<col class='diff-marker' />
<col class='diff-content' />
<tr style='vertical-align: top;' lang='en'>
<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 06:05, 10 September 2009</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l9" >Line 9:</td>
<td colspan="2" class="diff-lineno">Line 9:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The simplest viewshed calculations suppose that light moves in straight lines in a Euclidean space (the earth is not curved and no refraction occurs).  This is a good approximation for distances of several kilometers or miles.  Corrections for the earth's curvature and for optical refraction in the earth's atmosphere are needed for accurate results over longer distances.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The simplest viewshed calculations suppose that light moves in straight lines in a Euclidean space (the earth is not curved and no refraction occurs).  This is a good approximation for distances of several kilometers or miles.  Corrections for the earth's curvature and for optical refraction in the earth's atmosphere are needed for accurate results over longer distances.</div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">== See Also ==</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">http://www.landtrustgis.org/images/Deciding%20to%20Use%20GIS/Advanced/Advanced%20GIS%20software/2esrispatial_analyst_firevie.jpg/pop</ins></div></td></tr>
</table>WikiSysophttp://dbbd.sg/wiki/index.php?title=Viewshed&diff=4659&oldid=prevWikiSysop at 06:02, 10 September 20092009-09-10T06:02:29Z<p></p>
<p><b>New page</b></p><div>== Viewshed Calculations ==<br />
<br />
A "viewshed" is a region visible to an observer. "Visibility" refers to line of sight, but the same concept and calculations apply to transmission of signals in other media: radio and microwave frequency waves, sonar, and radar.<br />
<br />
Viewsheds can help answer many different kinds of questions:<br />
*How to situate infrastructure, such as pipelines and highways, in out-of-the way places that do not destroy the quality of natural scenery<br />
*Where to site transmission towers to avoid spatial gaps in reception<br />
*How to characterize regions under surveillance (or not under surveillance)<br />
<br />
The simplest viewshed calculations suppose that light moves in straight lines in a Euclidean space (the earth is not curved and no refraction occurs). This is a good approximation for distances of several kilometers or miles. Corrections for the earth's curvature and for optical refraction in the earth's atmosphere are needed for accurate results over longer distances.</div>WikiSysop