[Qgis-user] Extracting Raster values (time series) using polygons

[Ujaval]

Here's a step-by-step tutorial on the Zonal Statistics plugin
http://www.qgistutorials.com/en/docs/sampling_raster_data.html
You can use a custom field prefix for each of the rasters and you will have
columns representing stats for each of the year.

-Ujaval

On 06-Oct-2015 1:13 am, "Michael Treglia" <mtreglia at gmail.com> wrote:

> Hi Sam,
>
> Important point of clarification: Do you want all of the individual pixel
> values? Or aggregate statistics, like min/max/mean/med...?
>
> For the latter, there are a few tools you can use. I typically use a tool
> in the Processing Toolbox, implemented in SAGA: Go to Processing Toolbox -
> > SAGA -> Shape-Grid -> Grid Statistics and you'll be able to get those
> stats for your desired grids. The only downside, if i recall correctly, is
> that the column names don't necessarily indicate which layer the stats are
> from, if you're operating on multiple rasters at a time.  There's a  'Zonal
> Statistics'  tool also, which I think works well too. It is a plugin - it
> is a 'core plugin', which means it come with QGIS,though you might need to
> activate it (can't remember). If it is already activated, you'll see it
> when you go to the 'Raster' toolbar menu.  If you don't see it there, you
> can search for it in the 'Plugin' dialogue and make sure the box next to it
> is checked.
>
> (more details on plugins here:
> https://docs.qgis.org/2.8/en/docs/user_manual/plugins/plugins.html)
>
> If you want the former, that might be a bit more complicated, and is
> something I typically do directly in R, but could give advice here too.
>
> hope that helps!
> mike
>
> On Mon, Oct 5, 2015 at 1:39 PM, Sam Almond <sam_almond at hotmail.com> wrote:
>
>> Dear QGIS Users,
>>
>>
>>
>> I am new to using qGIS and can’t find an obvious solution to my problem.
>>
>>
>>
>> I have created a time series of NDVI rasters covering my area of
>> interest. The NDVI time series is derived from the Landsat imagery spanning
>> a decade of so. I also have a created a vector layer, consisting of
>> polygons, which represents digitized farmed fields (70 or so). The plan is
>> to use the polygons to extract the raster values from the time series,
>> ideally one year at a time. The ideal scenario is to be provided with the
>> pixel values per field (polygon) per NDVI over the year. Is this possible?
>> Help appreciated.
>>
>>
>> Many thanks
>>
>>
>> Sam
>>
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>
>
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