By inferring the threshold based on SampleDimension[] minimums, I really
just meant to use the minimum value as the threshold if its available, not
to compute it.
I did notice CoverageUtilities has a getMosaicThreshold() that seems to
attempt to ignore the threshold by setting it to data type minimums:
https://github.com/geotools/geotools/blob/master/modules/library/coverage/src/main/java/org/geotools/resources/coverage/CoverageUtilities.java#L633
Unfortunately I'm even finding that the JAI Mosaic operation seems to have
a bug where the source extender only sets the values on the first band. So
really I just can't wait for all of your good work on JAI-EXT and correct
no data handling to replace existing JAI utilities. I have a JAI-EXT Stats
operation in as a org.opengis.coverage.processing.Operation very similar to
how JAI-tools' Zonal stats was integrated as a geotools operation which I
can contribute if that will help.
On Fri, Feb 6, 2015 at 12:37 PM, Nicola Lagomarsini <
nicola.lagomars...@geo-solutions.it> wrote:
> Hi Rich,
>
> I think that inferring the threshold on the coverage could be slow (for
> example for BigTiff data). In JAI-EXT we introduced the concept of NoData,
> which will be used by the Mosaic operation instead of the old
> threshold value.
>
> Regards,
> Nicola Lagomarsini.
>
> 2015-02-03 22:22 GMT+01:00 Rich Fecher <rfec...@gmail.com>:
>
>> We've been using the geotools' resample operation to generally resize
>> rasters and have run into an issue. We have multiple bands with the double
>> data type and in the situation where the transform resolves to an identity
>> transform the resulting mosaic operation ends up masking some values. The
>> Resampler2D code sets null for sourceROI and sourceThreshold for the
>> MosaicDescriptor parameters which results in the default sourceThreshold of
>> 1.0 being used. The resulting MosaicOpImage then sets all values that are
>> less than 1.0 to the background value.
>>
>> Here's where the resampler uses the default parameters:
>>
>> https://github.com/geotools/geotools/blob/master/modules/library/coverage/src/main/java/org/geotools/coverage/processing/operation/Resampler2D.java#L631
>>
>> Here's then where jai uses the background values if the value doesn't
>> exceed sourceThreshold:
>>
>> https://github.com/mauricio/jai-core/blob/master/src/share/classes/com/sun/media/jai/opimage/MosaicOpImage.java#L2059
>>
>> In our case, we have valid values less than 1.0 and the background value
>> is NaN so we are effectively arbitrarily masking some of our values. I get
>> how we could just determine if the resample operation is going to result in
>> a Mosaic operation and then make sure the parameters are set to something
>> valid. But this is just one case and its nice that the resample operation
>> is generalized for us so we don't have to determine the underlying
>> operation.
>>
>> I'd think that the Resampler2D code could at least try to infer the
>> threshold as the minimum values from the GridSampleDimension[] of the
>> coverage. Does that make sense?
>>
>> I actually don't entirely get when this sourceThreshold is useful - as
>> long as the background and no data values for the source and destination
>> are the same it seems unnecessary. So perhaps in the spirit of eventually
>> using jai-ext this should be something that defaults as just not being used?
>>
>> Please let me know what path I should try to go down. Thanks,
>> Rich
>>
>>
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>
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