Feature Tile Link

Extension Title

Feature Tile Link

Introduction

This extension creates a link between a feature and tile table. A tile table containing tiles that represent or were generated from features can be linked to the feature table. The link enables feature queries when dealing with tiles representing features.

Extension Author

National Geospatial-Intelligence Agency, author_name nga

Extension Name or Template

nga_feature_tile_link

Extension Type

New Requirement

Applicability

This extension applies to the table names of feature user tables (2.1.6) and tile user tables (2.2.8).

Scope

Read-write

Requirements

GeoPackage

Extension Table Entry

The Feature Tile Link extension is registered into the gpkg_extensions table only once as follows:

`gpkg_extensions`
table_name	column_name	extension_name	definition	scope
null	null	`nga_feature_tile_link`	URL to this extension description	read-write

Feature Tile Link Table

The Feature Tile Link Table contains a user feature table and tile table name for linked tables.

`nga_feature_tile_link`
Column Name	Type	Description	Null	Default	Key
`feature_table_name`	TEXT	Feature user data table name	no		PK
`tile_table_name`	TEXT	Tile user data table name	no		PK


CREATE TABLE nga_feature_tile_link (
  feature_table_name TEXT NOT NULL,
  tile_table_name TEXT NOT NULL,
  CONSTRAINT pk_nftl PRIMARY KEY (feature_table_name, tile_table_name)
);

GeoPackage SQLite Configuration

None

GeoPackage SQLite Extension

None

Examples

The rivers GeoPackage has a rivers feature table linked to a rivers_tiles tile table. The tiles were generated from the features for zoom levels 0 through 6.

The example GeoPackage links feature tables to tile tables containing tiles generated from the features.