[Insight-developers] Addressing Failures of ResampleImageFilter9Test

[Bill Lorensen]

Tom,

I think we are both correct. It is a precision issue, but I think sse2
affects precision. At least that's what I can gather from :
http://en.wikipedia.org/wiki/SSE2

Bill

On Tue, Aug 18, 2009 at 5:21 AM, Tom
Vercauteren<tom.vercauteren at gmail.com> wrote:
> 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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>>
>