+1 to the blog including some geospatial technicalities
> On Sep 21, 2017, at 3:14 PM, Adam Estrada <[email protected]> wrote:
>
> +1 to the blog
>
> Sent from my iPhone
>
>> On Sep 21, 2017, at 1:56 PM, Chris Mattmann <[email protected]> wrote:
>>
>> Awesome benchmarking Martin.
>>
>> Would you like to write an ASF blog post about this, CC’ing Sally…
>>
>>
>>
>> On 9/21/17, 4:13 AM, "Martin Desruisseaux"
>> <[email protected]> wrote:
>>
>> A comparison of Apache SIS and Proj.4 has been posted in two blob posts:
>> one on performance aspects [1] and one on accuracy aspects [2]. We have
>> not been able to perform an extensive comparison yet, but more tests may
>> happen in 2018. In the meantime, below is a summary of some points:
>>
>> * Proj.4 is generally faster than Apache SIS on Java 8, apparently
>> because trigonometric functions are slower in Java 8.
>> * Some (but not all) trigonometric functions are much faster in Java
>> 9, but we have not yet benchmarked SIS on Java 9.
>> * Despite above handicap, Apache SIS is sometime faster than Proj.4
>> (400 times faster in an extreme case). This can be explained by more
>> extensive use of mathematical equivalences and runtime detection of
>> simplifications in Apache SIS.
>> * Apache SIS and Proj.4 are in close agreement for all tested
>> coordinate conversions (this category include map projections) on
>> Earth.
>> * Apache SIS and Proj.4 are sometime in disagreement by 1 or 2 meters
>> for coordinate transformations (this category include datum shifts).
>> o In the two cases were a disagreement is observed, Apache SIS is
>> conform to the parameters specified by the EPSG geodetic dataset.
>> o In one case, Proj.4 results are wrong by 0.9 ± 0.4 meter. This
>> is not a bug that could be easily fixed, but a Proj.4
>> architectural issue ("early-binding" versus "late-binding"
>> approaches). More details are given in the blog post.
>> o In the other case, one can argue that Proj.4 is not wrong
>> provided that the difference between Apache SIS and Proj.4
>> results are smaller than the stochastic errors associated to the
>> tested transformations. Apache SIS provides this information,
>> but not Proj.4. This lack of information makes difficult to
>> determine if the difference is acceptable or not.
>> * For Cylindrical Equal Area ("cea") projection on Jupiter (tested
>> because it is a more flattened planet than Earth):
>> o If Jupiter had the size of Earth (for easier distance
>> comparison), average Proj.4 error would be 90 meters.
>> o Apache SIS does not have this error; it keeps centimetric
>> precision.
>>
>> Those errors are not significant to everyone. But we need a way to tell
>> user if the library is delivering the accuracy that (s)he need, or if
>> (s)he got the operation for the right geographic area. Apache SIS
>> provides this information, notably through ISO 19162 (WKT 2) formatting.
>> This support is not yet widespread in other open source libraries.
>>
>> Martin
>>
>> [1]
>> https://www.geomatys.com/wordpress/index.php/2017/08/28/english-proj-4-versus-apache-sis-a-performance-comparison/?lang=en
>> [2]
>> https://www.geomatys.com/wordpress/index.php/2017/09/20/proj-4-versus-apache-sis-an-accuracy-comparison/?lang=en
>>
>>
>>
>>
