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You can do this with a couple of different interfaces, including a text file, which might work better in your case. The syntax is the same, however. It involves giving a cut point for the raster values and a color at that cut point. GRASS then will shade between
the cut points. For example:
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<div>0 red</div>
<div>10 blue</div>
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<div>…will make a 0 value red (255:0:0 in RGB), a value of 10 blue (0:0:255 in RGB) and grade from red to blue for all intermediate values.</div>
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<div>You can express the same thing with RGB values (note the colons separating the color values)</div>
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<div>0 255:0:0</div>
<div>10 0:0:255 </div>
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<div>If you're values vary but you always want them to scale between red and blue, you can also express this as</div>
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<div>0% red</div>
<div>100% blue</div>
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<div>You can mix and match raw values and percents, named colors and RGB values.</div>
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<div>In your particular case, you could do…</div>
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<div>0 yellow</div>
<div>1 yellow</div>
<div>7 purple</div>
<div>100% purple</div>
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<div>This makes 0-1 yellow, 7 purple, and everything above 7 purple. The other values will always grade between yellow and purple. If you want to put in some other cut points to make sure that particular values have particular colors, you can do so.</div>
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<div>0 yellow</div>
<div>1 yellow</div>
<div>3 green</div>
<div>5 red</div>
<div>7 purple</div>
<div>100% purple</div>
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<div>The result is…</div>
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<div>0-1 is yellow</div>
<div>1-3 grades between yellow and green</div>
<div>3 is green</div>
<div>3-5 grades between green and red</div>
<div>5 is red</div>
<div>5-7 grades between red and purple</div>
<div>7 on up is purple</div>
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<div>Hope this makes the r.colors less mysterious.</div>
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<div>Cheers</div>
<div>Michael</div>
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<div><font class="Apple-style-span" face="Helvetica" size="3"><span class="Apple-style-span" style="font-size: 12px; ">______________________________</span></font></div>
<div><font class="Apple-style-span" face="Helvetica" size="3"><span class="Apple-style-span" style="font-size: 12px; ">C. Michael Barton </span></font></div>
<div><font class="Apple-style-span" face="Helvetica" size="3"><span class="Apple-style-span" style="font-size: 12px; ">Director, Center for Social Dynamics & Complexity</span></font></div>
<div><font class="Apple-style-span" face="Helvetica" size="3"><span class="Apple-style-span" style="font-size: 12px; ">Professor of Anthropology, School of Human Evolution & Social Change</span></font></div>
<div><span class="Apple-style-span" style="font-size: 12px; font-family: Helvetica; ">Arizona State University</span></div>
<div><font class="Apple-style-span" face="Helvetica" size="3"><span class="Apple-style-span" style="font-size: 12px; ">Tempe, AZ 85287-2402</span></font></div>
<div><font class="Apple-style-span" face="Helvetica" size="3"><span class="Apple-style-span" style="font-size: 12px; ">USA</span></font></div>
<div><font class="Apple-style-span" face="Helvetica" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br>
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<div><font class="Apple-style-span" face="Helvetica" size="3"><span class="Apple-style-span" style="font-size: 12px; ">voice:<span class="Apple-converted-space"> </span><span class="Apple-tab-span" style="white-space: pre; ">
</span>480-965-6262 (SHESC), 480-727-9746 (CSDC)</span></font></div>
<div><font class="Apple-style-span" face="Helvetica" size="3"><span class="Apple-style-span" style="font-size: 12px; ">fax: 480-965-7671(SHESC), 480-727-0709 (CSDC)</span></font></div>
<div><font class="Apple-style-span" face="Helvetica" size="3"><span class="Apple-style-span" style="font-size: 12px; ">www: <span class="Apple-tab-span" style="white-space: pre; ">
</span><a href="http://csdc.asu.edu">http://csdc.asu.edu</a>, <a href="http://shesc.asu.edu">
http://shesc.asu.edu</a></span></font></div>
<div><font class="Apple-style-span" face="Helvetica" size="3"><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-tab-span" style="white-space: pre; "></span><a href="http://www.public.asu.edu/~cmbarton">http://www.public.asu.edu/~cmbarton</a></span></font></div>
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<div>On Mar 28, 2013, at 5:54 AM, Nathan Barber - NOAA Federal <<a href="mailto:nathan.barber@noaa.gov">nathan.barber@noaa.gov</a>> wrote:</div>
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We generate a precipitation graphic that is based on the mean of an ensemble of models. Because it goes out 16 days, we can have a wide variety of amounts...sometimes it can be as little as 2 inches other times it can be as great as 6 or 7. This variability
can cause some issues with users when our color scale always changes relative to the amounts. For example Day 1, 1 inch is yellow and 3 inches is purple....Day 2, 2 inches is yellow and 6 inches is purple.
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Is there a way to categorize amounts, say 0-1, 1-2, 2-3, 4-5, 5-6, 7+ so that purple will always represent 7+ and yellow will always be 0-1, etc...I've looked at the r.colors wiki page but I can't seem to get the rules to work correctly. I need a consistent
color scheme for the graphic that communicates the level of concern properly to the user.
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Any examples would be greatly appreciated...Thanks.<br clear="all">
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-- <br>
<div style="text-align:left">Nathan Barber<br>
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<div style="text-align:left">Hydrologist<br>
<div>NOAA National Weather Service<br>
<a href="http://www.erh.noaa.gov/ohrfc/" target="_blank">Ohio River Forecast Center</a><br>
1901 S State Rt 134<br>
Wilmington, OH 45177<br>
(937) 383-0528<br>
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