Need buffered point to extract raster pixel value when overlapping >1  pixel

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11-28-2013 01:30 PM
AOrlich
New Contributor
Hello,

I have a raster of 25km2 and point features with lat/lon. I have successfully extracted all raster values with the points in the lat/lon data set from the raster, but then wanted the points to be buffered by 1nmi, I can't seem to find a way to have the buffered area extract the raster values. What I want is to be able to so is get the average (weighted?) for the raster value when a buffered point overlaps one or more raster pixels.

Is this possible?

Thank you for any clues or direction!

And Happy Thanksgiving to ALL~

~Alice
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3 Replies
Luke_Pinner
MVP Regular Contributor
Use the Focal Statistics tool, set statistic to "Mean" and neighbourhood to NbrCircle(radius, "MAP"). If your map units units are metres and you want a 1 nautical mile "buffer" use a radius of 1852.  This will output a new raster where each cell is assigned the average of all cells from the original raster that are within a 1nmi radius.  Then use the Extract Values To Points tool to get the values for your point features.
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AOrlich
New Contributor
Ipinner~

Thank you for your response. I think I communicated my issue poorly. The result I'm looking for is the raster value of the buffered point.

So if my lat/lon point fell into a cell with a value of 25, but after a 1nm or 1852m buffer, it crossed about half of its area in the buffer into a cell with a value of 75, I'd hope to get a weighted average of the 2 cells which the buffered zone covered, expecting a result around 50 (realizing that before the buffer, the point confidently fell within the cell with a value of 25 and then had a near equal amount cover the cell with a value of 75).

The Focal Stats tool is averaging the raster's cells within the buffer distance to the original raster cell values. I need the lat/lon point to represent a 1nm radius of the exact lat/lon. When the point is buffered, it becomes a polygon. Is there a way to extract the raster cell values, averaged if necessary, which a polygon covers?

Thanks again,
Alice
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Luke_Pinner
MVP Regular Contributor
I'm still not sure what you are trying to do? In your example of a buffer crossing 2 cells with values of 25 and 75, the focal stats method I describe would give you the value 50 that you expect.

If you actually buffer the points and create a vector polygon, then use the zonal statistics as table tool to extract the average, you will get exactly the same answer, but you have the overhead of creating the buffer which ArcGIS will then convert back to a raster behind the scenes before extracting the mean value. Another drawback to this method is that buffers that overlap can't be processed.
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