[Insight-developers] Addressing Failures of ResampleImageFilter9Test

[Tom Vercauteren]

Hi Bill,

Further testing seems to support the fact that this is not a sse2
rounding issue but rather a numerical precision one that cannot be
avoided.

To be more specific, in "real math" we should have
    0.4 + 6*0.35 == 2.5
with floating point arithmetic, on some systems, we might have
    0.4 + 6*0.35 == 2.5
whereas on others the same operation might lead to
    0.4 + 6*0.35 < 2.5

It appears that the test is failing because of exactly that. The
origin is 0.4 the spacing is 0.35, the first pixel that shows a
difference is the 6th one and further failing pixels are located every
20 pixels (note that 20*0.35=7 is the first integer value we can get).

I would vote for making the comparison less stringent. Thoughts?

Tom

P.S. The attached small test case illustrate the numerical precision
"issue" above and shows that this is apparently unrelated to sse2
rounding.


On Tue, Aug 18, 2009 at 09:17, Tom Vercauteren<tom.vercauteren at gmail.com> wrote:
> Hi Bill,
>
> Thanks for investigating this. VNL_CONFIG_ENABLE_SSE2_ROUNDING is
> meant to have no effect (except speed) on the results. If it has, it's
> a bug.
>
> I'll try and get some time to look into this issue.
>
> Tom
>
> On Mon, Aug 17, 2009 at 19:51, Bill Lorensen<bill.lorensen at gmail.com> wrote:
>> Luis,
>>
>> I believe I found the partition. I checked most (not all)
>> CMakeLists.txt files (in the itkSystemInformationTest output) for
>> passing and failing platforms.
>>
>> Here is what I concluded:
>>
>> Platforms that are failing have a common cmake variable set:
>> //Enable Streaming SIMD Extensions 2 implementation of rounding
>> // (hardware dependant).
>> VNL_CONFIG_ENABLE_SSE2_ROUNDING:BOOL=ON
>>
>> those that are passing have one of two conditions:
>>
>> 1) ITK_USE_CENTERED_PIXEL_COORDINATES_CONSISTENTLY:BOOL=OFF
>> or
>> 2) VNL_CONFIG_ENABLE_SSE2_ROUNDING:BOOL=OFF
>>
>> Should we expect the same results regardless of the SSE2 setting? If
>> not, then we can check in another baseline. If the results should be
>> the same, we have some work to do.
>>
>> Bill
>>
>>
>> On Sun, Aug 16, 2009 at 12:30 PM, Luis Ibanez<luis.ibanez at kitware.com> wrote:
>>>
>>> FYI:
>>>
>>> The test  "ResampleImageFilter9Test":
>>>
>>> Has been failing since we enabled the flag
>>>
>>> ITK_USE_CENTERED_PIXEL_COORDINATES_CONSISTENTLY
>>>
>>> What seems to be special about this test is that it runs
>>> on an image of RGBPixels, and therefore, it uses:
>>>
>>> itk::VectorResampleImageFilter  and
>>> itk::VectorNearestNeighborInterpolateImageFunction
>>>
>>> What is curious, is that is passes on some machines and fails
>>> on others, and it doesn't seem to be a clear partition between
>>> the two groups, (see this link):
>>> http://www.cdash.org/CDash/testSummary.php?project=2&name=ResampleImageFilter9Test&date=2009-08-16
>>>
>>>
>>> We will be following on this during the week....
>>>
>>>
>>> Any suggestions/hints are welcome...
>>>
>>>
>>>      Thanks
>>>
>>>
>>>          Luis
>>>
>>>
>>>
>>>
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