<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">I would not use gdal for this particular task. I presume you have the band data in a 2D numpy array. Then I’d get the 80th percentile for example with np.percentile() and use a boolean expression to generate a mask for the array (droneraster > perc80value ).<div class=""><br class=""></div><div class="">Chris<div class=""><div class=""><br class=""><div class="">
<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Consolas; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; border-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-stroke-width: 0px;"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; border-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-stroke-width: 0px;"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; border-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-stroke-width: 0px;"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; border-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-stroke-width: 0px;"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><span class="Apple-style-span" style="font-family: monospace;">-- </span></div><div class=""><span class="Apple-style-span" style="font-family: monospace;">Christine (Chris) Waigl - <a href="mailto:cwaigl@alaska.edu" class="">cwaigl@alaska.edu</a> - +1-907-474-5483 - Skype: cwaigl_work</span></div><div class=""><span class="Apple-style-span" style="font-family: monospace;">Geophysical Institute, </span><span class="Apple-style-span" style="font-family: monospace;">UAF, </span><span class="Apple-style-span" style="font-family: monospace;">903 Koyukuk Drive, </span><span class="Apple-style-span" style="font-family: monospace;">Fairbanks, AK 99775-7320, USA</span></div><div class=""><br class=""></div></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"><br class="Apple-interchange-newline">
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<br class=""><div><blockquote type="cite" class=""><div class="">On Aug 3, 2017, at 5:43 AM, Paul Meems <<a href="mailto:bontepaarden@gmail.com" class="">bontepaarden@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">I have a drone raster file which I want to use for some calculation.<div class="">Before the calculation, I need to loose some extreme values.</div><div class="">I want to do something like a percentile calculation where you get all values, order them and loose the top 10%.</div><div class="">For this, I need to get all values first which can be slow when using a large file.</div><div class=""><br class=""></div><div class="">I looked at the statistics (band.GetStatistics) but that doesn't work well.</div><div class="">I thought I could use 2 times the standard deviation added to the mean to get roughly 97%.</div><div class="">But with these statistics:</div><div class=""><div class=""><font face="monospace, monospace" class=""> STATISTICS_MAXIMUM=33.186080932617</font></div><div class=""><font face="monospace, monospace" class=""> STATISTICS_MEAN=24.840205979603</font></div><div class=""><font face="monospace, monospace" class=""> STATISTICS_MINIMUM=1.5951598882675</font></div><div class=""><font face="monospace, monospace" class=""> STATISTICS_STDDEV=4.7285348016053</font></div><div class="">Mean + 2*std is larger than the max.</div><div class=""><br class=""></div><div class="">So I moved to the histogram. It is also very fast, but I'm not sure how to use it.</div><div class="">I have this:</div><div class=""><div class=""><font face="monospace, monospace" class=""> 256 buckets from 1.53322 to 33.248:</font></div><div class=""><font face="monospace, monospace" class=""> 410 77 66 66 65 58 56 45 42 87 57 72 61 65 68 70 73 82 93 ...</font></div></div><div class=""><div class="gmail_signature"><div dir="ltr" class=""><div dir="ltr" class=""><div dir="ltr" class=""><div dir="ltr" class="">Does this mean, bucket 1 = 410 that I have 410 pixels of value 1.53322 and the second bucket means I have 77 pixels between 1.53322 and 1.657? 1.657 = 1.53322 + ((33.248 - 1.53322)/256)</div><div dir="ltr" class=""><br class=""></div><div dir="ltr" class="">Is this a good approach? Or can/should I use a different one.</div><div dir="ltr" class=""><br class=""></div><div dir="ltr" class="">Thanks,<br class="">
<br class="">Paul<br class="">
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