82 lines
4.2 KiB
HTML
82 lines
4.2 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="CONTENT-TYPE" content="text/html; charset=utf-8">
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<title>LimitValues</title>
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<meta name="GENERATOR" content="OpenOffice.org 1.1.3 (Linux)">
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<meta name="CREATED" content="19951121;16410000">
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<meta name="CHANGED" content="20050706;13040400">
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<style>
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<!--
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@page { size: 8.5in 11in; margin-right: 1.25in; margin-top: 1in; margin-bottom: 1in }
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P { margin-bottom: 0.08in; direction: ltr; color: #000000; text-align: left; widows: 0; orphans: 0 }
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P.western { font-family: "Bitstream Vera Serif", "Times New Roman", serif; font-size: 12pt; so-language: en-US }
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P.cjk { font-family: "Bitstream Vera Sans"; font-size: 12pt; so-language: }
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P.ctl { font-family: "Lucidasans"; font-size: 12pt; so-language: }
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-->
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</style>
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</head>
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<body dir="ltr" lang="de-DE" text="#000000">
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<font face="New Century Schoolbook, Times New Roman, serif"><font
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size="5"><b>LimitValues</b></font></font>
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<br>
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<br>
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<font face="New Century Schoolbook, Times New Roman, serif"><font
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size="3"><b>Introduction</b></font></font>
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<br>
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<br>
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<font face="New Century Schoolbook, Times New Roman, serif">Sometimes it is desirable to “clip”
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grid values to particular limits. For example, you might not want temperatures to cross some
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important threshold such as 32 or 100. There are a variety of tools you might use that would
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allow you to raise/lower values over a region such that the values do not cross these thresholds.
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However, depending on the color curve, it may be difficult to see if any pixels reach these
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values, and using other tools might inadvertently change other pixels that you want to remain
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constant.
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<br><br>
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The Limit_Values tool clips grid values at limits that you specify. It is purely an “editing”
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tool, with no meteorological “theory” behind it - it is simply a quick way to accomplish a
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common editing task. It is similar to the “NoHigherThan” and “NoLowerThan” tools by Thomas
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Mazza, but it combines the two tools in one, and when you start the tool, the slider shows
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the current value - which makes modifications easier.</font>
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<br>
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<br>
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<br>
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<big><big><font style="font-weight: bold;"
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face="New Century Schoolbook, Times New Roman, serif">How
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the Procedure Works</font><span style="font-weight: bold;">
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</span></big></big><br>
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<br>
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<font face="New Century Schoolbook, Times New Roman, serif">Lets say we start with a complex temperature pattern like this:<br><br>
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<img alt="LimitValues" src="images/LimitValues.png"></font>
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<br>
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<br>
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<font face="New Century Schoolbook, Times New Roman, serif">Lets say that for some reason, we do
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not believe any of the locations near the center of the screen will be in the 90s. There are
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quite a few non-contiguous pixels above 90, so it will be difficult to remove them without also
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editing other nearby points. For some reason, lets say that we just want to set the temperature
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to 89 in those areas. We could create a complex query of edit areas, areas where temperatures
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are above 89, etc. and then use the Assign_Value tool to assign 89 to those points. That
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approach is complex and takes many steps.
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<br><br>
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With the Limit_Values tool, we simply draw a general edit area that covers the points in
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question:<br>
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<img alt="LimitValues" src="images/LimitValues1.png"></font>
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<br>
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<br>
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<font face="New Century Schoolbook, Times New Roman, serif">Then we call the Limit_Values tool
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and a dialog box comes up with the current max/min values in the current edit area:<br>
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<img alt="LimitValues" src="images/LimitValues2.png"></font>
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<br>
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<br>
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<font face="New Century Schoolbook, Times New Roman, serif">Now we can see that some pixel in
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the edit area was 96 (which is difficult to tell with the color curve we are using)! Now we
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simply set the maximum value to 89:<br>
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<img alt=LimitValues" src="images/LimitValues3.png"><br><br>
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And when we click on OK, all the pixels above 89 in the edit area are set to 89:<br>
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<img alt="LimitValues" src="images/LimitValues4.png"><br><br>
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You can limit the minimum value on the grid in a similar way. You can certainly run the tool
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without defining an edit area, in which case it acts upon the entire grid.
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</font>
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</body>
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</html>
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