[Geopackage] New blog post: what about vector tiles in GeoPackage?

Adam Parsons aparsons at compusult.net
Fri Jun 29 14:36:07 EDT 2018


Hey Jeff,


I have already implemented some vector tiles GeoPackages previously for 
some OGC test bed, though it was in GeoJSON format. From my experience I 
have some questions/comments.

Possibly these questions will arise from now knowing the Protocol Buffer 
implementation that well.


1)


        |gpkgext_vt_layers|

Why do we need to explicitly describe what the min and max zoom level is 
for a layer? Wouldn't this be described in a tile matrix set table just 
like raster?
     - If we do not need this concept, then why would we need a layers 
table that is different then contents table? to describe multiple layers 
inside of a vector tile?

2)


        |gpkgext_vt_fields|

Why can we not reuse the gpkg_data_columns table? Is it because if we 
have multiple layers inside of a tile then we cannot actually reference 
a TABLE name?


3) Data type

     - You are going for a Google Protocol Buffer. Couldn't we support 
multiple formats GeoJSON or GPB based on the data-type of the 
gpkg_contents table?

4) Layer concept

     - Does it make more sense to have a tile composed of multiple 
layers? Or does it make more sense to have a layer by tile basis? 
Processing would require parsing out tile content and doing explicit 
operations to determine things on a per layer basis


Furthermore, when I first implemented the GeoJSON format for vector 
tiles, I basically had to not add any auxiliary tables and could use the 
current GPKG core model and just add a new data-type and some extension 
entries.


Finally, when implemented there were 2 key concepts that I had to 
introduce for optimization;

1) An 'ANCHOR' tile which held all feature meta-data information in 1 
single tile (A tile on the highest zoom level for that feature to reduce 
putting all feature information in 1 tile). All other tiles containing 
that feature would reference the ANCHOR feature meta-data tile (This was 
described as an attribute inside of the GeoJSON)

2)A way of describing the CLIP indices for a feature, when it has to 
clip the geometry based on a tiles boundaries, to ensure a client can 
easily reconstruct an entire feature geometry from partial tile vertexes 
for a feature. (This was described as an attribute inside of the GeoJSON)


Thanks,
Adam


On 2018-06-29 11:51 AM, Jeff Yutzler via Geopackage wrote:
> Based on the feedback I got from this post, I went ahead and drafted a 
> community extension for vector tiles:
> https://github.com/jyutzler/geopackage-vector-tiles/blob/master/spec/1_vector_tiles.adoc
> I'd like for this to at least be the starting point for any use of 
> Vector Tiles in GeoPackage, but there is a long way to go before this 
> becomes a standard.
> -Jeff
>
>
> 2018-06-27 14:53 GMT-04:00 Jeff Yutzler <jeffy at imagemattersllc.com 
> <mailto:jeffy at imagemattersllc.com>>:
>
>     http://geopackage.blogspot.com/2018/06/what-about-vector-tiles-in-geopackage.html
>     <http://geopackage.blogspot.com/2018/06/what-about-vector-tiles-in-geopackage.html>
>
>     -- 
>     Jeff Yutzler
>     Image Matters LLC <http://www.imagemattersllc.com/>
>     Mobile: (703) 981-8753
>
>
>
>
> -- 
> Jeff Yutzler
> Image Matters LLC <http://www.imagemattersllc.com/>
> Mobile: (703) 981-8753

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