galbiston commented on issue #557: JENA-664 GeoSPARQL Jena
URL: https://github.com/apache/jena/pull/557#issuecomment-486419457
 
 
   I had the SIS_DATA dependency resolved in Gradle for testing both modules by 
"testImplementation "org.apache.sis.non-free:sis-embedded-data:$sisVersion". I 
don't think there is an equivalent for Maven for test only. Due to the 
licensing conflict between EPSG and AL2 I didn't include it as a non-test 
dependency.
   
   The other two warnings are to do with precision in transformations from the 
UK's OSGB36 to WGS84. OSGB36 was just an arbritary choice to use a planar 
coordinate system and conversions from WGS84. I can change the relevant test 
data to one of the main coordinate reference systems and it should make the 
warnings go away. There will just be this underlying configuration of the 
Apache SIS framework.
   
   I asked Martin Desruisseaux from Apache SIS about the warnings and his 
response is below.
   
   "For the warning that you get, actually I should improve the error message. 
I presume that the “OSTN15_NTv2_OSGBtoETRS.gsb” datum shift file is not present 
on your system, so the error message should be "Can not find 
OSTN15_NTv2_OSGBtoETRS.gsb datum shift file". In such case Apache SIS will use 
a less accurate fallback (more on it later).
   
   The SIS_DATA environment variable is used not only for the EPSG database, 
but also for all other kind of data that SIS may need, including datum shift 
files. The EPSG embedded database is more convenient, but does not provide any 
datum shift files yet. We may include some datum shift files in 
sis-embedded-data in the future, but I don't think we could include all of them 
for space (and sometime licensing) reasons. Note also that I noticed that the 
embedded Derby database in a compressed JAR file is at least 5 times slower 
than a Derby database as ordinary files in a directory.
   
   If you want to give a try to SIS_DATA, you can create a DatumChanges 
sub-directory in the SIS_DATA directory and put the OSTN15_NTv2_OSGBtoETRS.gsb 
file there (we can download it from internet). You may also opportunistically 
replace sis-embedded-data module by sis-epsg for better performances (it will 
create the Derby database in that directory). If you prefer to keep 
sis-embedded-data for convenience, then you can ignore those warnings. SIS 
could be improved for making those warnings less disruptive to the users, but 
we have not determined yet how. In any case, I recommend to take a look at the 
output of System.out.println(theCoordinateOperation) and check in particular 
the value inside OperationAccuracy[...] element. The value will be different 
depending if the datum shift file has been found or not; it is up to the 
application to decide if the reported accuracy if sufficient for their needs."

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