Use NTv2 grid files in SpatiaLite ST_Transform

[Antonio Valanzano]

I am thinking of buying from  the "Italian Geographic Military Service"   some .gsb files for doing some coordinate transformations between different CRSs with the best precision.

Does someone know how to use this files in Spatialite ?

Thanks 

Antonio

[phi...@gmail.com]

Hi Antonio,

according to documentation you should be able to use PROJ strings:

https://www.gaia-gis.it/gaia-sins/spatialite-sql-5.1.0.html

ST_Transform( geom Geometry , newSRID Integer , area_of_use Geometry , proj_string_from Text , proj_string_to Text ) : Geometry

Here is one example that uses NTv2 file:

FROM:

+proj=tmerc +lat_0=0 +lon_0=16.5 +k=0.9999 +x_0=500000 +y_0=0 +ellps=GRS80 +units=m +towgs84=0,0,0,0,0,0,0

TO

+proj=tmerc +lat_0=0 +lon_0=15 +k=0.9999 +x_0=5500000 +y_0=0 +ellps=bessel +nadgrids=./HRNTv2.gsb +units=m

[Antonio Valanzano]

Thanks for the info.

I will read the documentation more thoroughly.

Antonio