[SEDONA-368] Add RS_SummaryStats #978
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| private static double getStddev(double[] pixels, double mean) { | ||
| double stddev = 0; | ||
| for(double pixel: pixels){ | ||
| stddev += Math.pow(pixel - mean, 2); | ||
| } | ||
| return Math.sqrt(stddev/(pixels.length - 1)); | ||
| } |
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Do we need to exclude pixels with nodata value when computing std-dev?
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I think so as nodata is not always 0, it can be -9999. Refer: https://desktop.arcgis.com/en/arcmap/latest/manage-data/raster-and-images/nodata-in-raster-datasets.htm#:~:text=NoData%20is%20stored%20as%20a,common%20value%20for%20storing%20NoData.
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We should include/exclude no data values in std based on the flag.
| } | ||
| } | ||
| } | ||
| mean = sum / count; |
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We need to be aware of the cases when all pixels in the band are nodata value. PostGIS returns all statistics except count as NULL. I think both NULL and NaN are sane choices.
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Okay, will add a check before the compute code and return NULL.
| for (double pixel: pixels) { | ||
| sum += pixel; | ||
| if (pixel < min) { | ||
| min = pixel; |
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both of these for loops can be merged
| private static double getStddev(double[] pixels, double mean) { | ||
| double stddev = 0; | ||
| for(double pixel: pixels){ | ||
| stddev += Math.pow(pixel - mean, 2); | ||
| } | ||
| return Math.sqrt(stddev/(pixels.length - 1)); | ||
| } |
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We should include/exclude no data values in std based on the flag.
| for(double pixel: pixels){ | ||
| stddev += Math.pow(pixel - mean, 2); | ||
| } | ||
| return Math.sqrt(stddev/(pixels.length - 1)); |
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standard deviation for a sample requires dividing by (n - 1). Since we're not sampling yet and are considering all pixels, we should be dividing by n.
| @@ -74,6 +74,116 @@ public void testBandNoDataValueIllegalBand() throws FactoryException, IOExceptio | |||
| assertEquals("Provided band index 2 is not present in the raster", exception.getMessage()); | |||
| } | |||
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| @Test | |||
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For the tests, since we're dealing with means and std which are small, can we see if delta of 1e-6 is sufficient instead of 0.1d?
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[SEDONA-XXX] my subject.What changes were proposed in this PR?
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