Pass current zoomlevel to query parameter of PostgreSQL vector provider

[shr3k]

Hi, it would be great to pass current zoomlevel to variable and allow PostgreSQL query adjustment.

Imagine we have a table with multiple pregeneralized geometry columns and we want to switch between them depending on currrent zoom level to spare some data and speed up client SVG rendering.

This is currently IMHO realizable with tilestache-seed.py - seed only selected levels and modify .cfg file to adjust desired geometry column.

It would be great to have .cfg like (very simplified idea, in fact there's need to have own function to select right geometry column):

"provider": {
"name": "vector",
"driver": "PostgreSQL",
"parameters": {"user": "postgis", "password": "mypassword", "dbname": "mydatabase", "query": "SELECT CAST(code AS character) AS code, name, geom_$ZOOMLEVEL FROM mytable"},
"properties": ["code","name"],
"clipped": false,
"id_property": "code"
}

Alternatively we could have some kind of zoom-geometry column mapping like:

"provider": {
"name": "vector",
"driver": "PostgreSQL",
"parameters": {"user": "postgis", "password": "mypassword", "dbname": "mydatabase", "table": "mytable"},
"zoom_to_geometry_mapping": {"13": "geom_simplify50m", "14": "geom_simplify25m", "15": "geom_simplify10m", "16": "geom_simplify10m", "17": "geom", "18": "geom"}
"properties": ["code","name"],
"clipped": false,
"id_property": "code"
}

[rburhum]

Hi shr3k,

Just wondering why having different layer definitions for different levels and changing the layers in js would not cut it...

[migurski]

Mapnik has a "scale denominator" value that you can put in psql queries, would something like that work?

[ckotil2]

Is it possible to pass anything back to Tilestache from the browser? My GeoJSON tiles are very large to the point it's slow to load them all at low zoom levels. I would like to be able to pass back say a layer_id that can then be used in the query to retrieve the GeoJSON data. It could be used to pass in zoom level as well.
Does this exist? Otherwise it's looking like I will need to have a few hundred layers defined in tilestache.cfg.