Hi Greg,
This isn't going to be an authoritative answer, I'm also just humble
user ;-) but the way I achieve something similar is by using the
OperationJAI class and the Histogram operation (have a look here as well
http://www.nabble.com/First-cut-of-statistics-operations-(Histogram-and-Extrema)-td12389138.html
).
I do something along these lines
GridCoverage coverage = reader.read(requestParams);
OperationJAI op=new OperationJAI("Histogram");
ParameterValueGroup param = op.getParameters();
param.parameter("Source").setValue( coverage );
param.parameter("roi").setValue( roi ); GridCoverage2D
histc = (GridCoverage2D) op.doOperation(param, null);
Histogram hist = (Histogram) histc.getProperty("histogram"); int[]
bins = hist.getBins(0);
- where coverage is a GridCoverage obtained from reading the GeoTiff and
roi is an ROIShape containing the query footprint. To some extent this
code comes from examples online e.g. with the Histogram docs
For the roi you will have to transform from the query footprint (i.e.
the national boundary in your case) from world space to grid space. Note
the grid space origin is top-left and it's integer. The easiest
(laziest?) way to convert is to use the transformer on the coverage i.e.
coverage.getGridGeometry().getGridToCRS().inverse(); and then round
values to nearest int.
I should add I've been working with discrete coverages rather than
continuous ones so I think you'll need to do some other things to
specify the ranges of the histogram bins...hopefully someone more
experienced will chime in here. I've never used the select() method and
from the docs don't entirely understand what it does, looking at the
source code it appears to be unimplemented at the moment anyway.
I need to do something similar in a bit so I'd be interesting hearing
how you finally solve this.
Cheers Alistair
Greg Ederer wrote:
> Hi,
>
> I have a shape file that defines national boundaries. I also have a
> GeoTiff containing rainfall data. I want to obtain a collection of the
> rainfall pixel values within a given national boundary. Is
> Coverage.select() the correct method to use for this?
>
> Any suggestions greatly appreciated.
>
> Greg
>
>
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