Timeline for Resampling gives higher MEAN when using zonal statistics
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| Dec 7, 2015 at 12:00 | answer | added | Cicatrixx | timeline score: 1 | |
| Dec 1, 2015 at 14:56 | comment | added | whuber | Involving projections is complicating the issue, because now we have to wonder about the interactions among the reprojection (which inherently resamples), the resampling, how areas are computed, and exactly how you are carrying out all these operations. It would be a good idea to isolate the problem by sticking to one coordinate system and studying how just the resampling affects the results. | |
| Dec 1, 2015 at 9:48 | comment | added | Cicatrixx | @whuber I have added some figures showing my comparison. I still see the zonal means are higher with resampled raster. Just wondering, my raster values are between 0-1. Does that make a difference perhaps? | |
| Dec 1, 2015 at 9:47 | history | edited | Cicatrixx | CC BY-SA 3.0 |
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| Dec 1, 2015 at 9:38 | history | edited | Cicatrixx | CC BY-SA 3.0 |
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| Dec 1, 2015 at 7:11 | comment | added | Cicatrixx | When I multiply the zonal means by the polygon areas, my values are almost twice that of what I expected. I did a total at the country level using a polygon with just the country boundary and compared that to the total I get for the regions within the country. I'm interested in only 75% of the regions within the country. I'll try doing the calculation again using the Union of both regions and country boundary as you suggest with the universal polygon. Maybe that will help | |
| Dec 1, 2015 at 0:41 | comment | added | whuber | Certainly the new means will change, because the resampling usually changes the weights of cells that are only partially covered by any polygon. (Isn't that the entire point of the procedure in this instance?) As a consistency check, you could multiply the polygon areas by the zonal means and total those over the polygons. These totals can change, too, but they should not change a whole lot--and if you include a surrounding "universal" polygon in the calculation, the only differences should be due only to floating point (single precision!) error. Do you observe that consistency or not? | |
| Nov 30, 2015 at 22:57 | history | edited | PolyGeo♦ | CC BY-SA 3.0 |
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| Nov 30, 2015 at 22:55 | history | edited | Cicatrixx |
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| Nov 30, 2015 at 22:53 | history | edited | PolyGeo♦ | CC BY-SA 3.0 |
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| Nov 30, 2015 at 22:52 | history | asked | Cicatrixx | CC BY-SA 3.0 |