<div>It's to help me double check my interpretation of a large dataset.</div><div><br></div>I have a collection of millions of traffic tickets. Each ticket has route name, milepost, and lat/long. I want to see how well the tickets of a particular route/milepost are to each other.<div>
<br></div><div>E.g., all tickets written for US 71, milepost 204--if they have a very large dispersion, then either I have an error in my analysis or the data is not good.<br><div><br></div><div><div>Aren<br><br><div class="gmail_quote">
On Sat, May 28, 2011 at 2:32 AM, Ben Madin <span dir="ltr"><<a href="mailto:lists@remoteinformation.com.au">lists@remoteinformation.com.au</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div style="word-wrap:break-word">I'm not quite clear to me what you are trying to demonstrate - do you want to know the density of the points... relative to their total size (area / number?), or relative to some defined area?<div>
<br></div><div>cheers</div><div><br></div><div>Ben</div><div><br></div><div><br><div><div><div></div><div class="h5"><div>On 28/05/2011, at 6:19 AM, Aren Cambre wrote:</div><br></div></div><blockquote type="cite"><div><div>
</div><div class="h5">Did anyone have thoughts on this? :-)<div><br></div><div>Aren<br><br><div class="gmail_quote">On Wed, May 4, 2011 at 2:12 PM, Aren Cambre <span dir="ltr"><<a href="mailto:aren@arencambre.com" target="_blank">aren@arencambre.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">The more I think about it, is this a job for R? I know I need to start using R at some point, just haven't begun yet.<div>
<br></div><div><font color="#888888">Aren</font><div><div></div><div><br><br><div class="gmail_quote">On Wed, May 4, 2011 at 1:42 PM, Aren Cambre <span dir="ltr"><<a href="mailto:aren@arencambre.com" target="_blank">aren@arencambre.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Suppose you have a geometry type with a multipoint. How would you calculate the variance of the points in that multipoint?<div>
<br></div><div>I looked through the PostGIS 1.5 function reference and am not coming up with any easy way.</div>
<div><br></div><div>A hard way seems to be using st_centroid(multipoint) to find the multipoint's center. From there, I can calculate the distance of each point from its center, and use that towards calculating the variance (each distance is squared, all squared distances are added together, then divide by number of points).</div>
<div><br></div><div>I guess my ultimate need is to measure relative dispersion of multipoints. The multipoints that have the most dispersion are suspect, but I need a way of identifying which ones are like this.</div><div>
<br></div><font color="#888888"><div>Aren</div>
</font></blockquote></div><br></div></div></div>
</blockquote></div><br></div></div></div><div class="im">
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