Hi Danh, this probably doesn't directly answer your query but just fyi with the release of Tableau 2019.1 you can now access Google BigQuery by connecting to your data directly from the web.
[Program Manager - Tableau Community]
Tableau supports native spatial data from spatial file formats (Esri Shapefiles, KML, geojson, MapInfo tables, topojson, Esri File Geodatabases) and SQL Server. We are planning to support spatial data directly from PostgreSQL+PostGIS. Support for other databases is something that we are interested in looking beyond our near-term roadmap.
To work with this data today, you would need to export it out of BQ and into a format Tableau can read directly.
I will try to update this thread if anything changes.
Thanks for the update, Kent