Related Standards and SWGs

OGC WMTS

See OpenGIS Web Map Tile Service Implementation Standard

An early version was Tile_Map_Service developed by the Open Source Geospatial Foundation, supported by the OpenLayers JavaScript library. Specification. Open source servers include:

• TileCache
• GeoWebCache
• MapProxy
• ROK4
• MapServer MapCache

OpenStreetMap provides Slippy Map Tilenames, or XYZ, interface based on the Leaflet javascript library, which is an off-shoot of OpenLayers, and use these conventions:

• Tiles are 256x256 pixels
• At the outer most zoom level, 0, the entire world can be rendered in a single map tile.
• Each zoom level doubles in both dimensions, so a single tile is replaced by 4 tiles when zooming in. This means that about 22 zoom levels are sufficient for most practical purposes.
• The Web Mercator projection is used, with latitude limits of around 85 degrees.
• An X and Y numbering scheme
• PNG images for tiles
• Images served through a REST API, with URL like http://.../Z/X/Y.png, Z is the zoom level, and X, Y identify the tile.

Google Maps and the Google Maps API uses these conventions:

• Tiles are 256x256 pixels
• At the outer most zoom level, 0, the entire world can be rendered in a single map tile.
• Each zoom level doubles in both dimensions, so a single tile is replaced by 4 tiles when zooming in. This means that about 22 zoom levels are sufficient for most practical purposes.
• The Web Mercator projection is used, with latitude limits of around 85 degrees.

OGC WMTS Simple Profile

http://www.opengeospatial.org/standards/requests/122

OGC WCS2.0

tbd

W3C Tiling and Layering Module for SVG1.2 Tiny

This was proposed in June 2011 to tackle the Level of Detail problem when using SVG pictures on mobile devices. The SVG WG is working on SVG2, and does not seem to be actively considering this module. Official comment is here. the module has four major components:

1. A standardized coordinate mapping for establishing geographic coordinates within the SVG coordinate space (CRS84, a variant of WGS84). This would be capable of ~10 cm precision on the earth, though positional inaccuracy could be ~10 kms. Specifying SVG CRS metadata with RDF/GML already possible, proposed 'globalCoordinateSystem' simpler. Assume affine transformations;
2. A tiling mechanism to allow large large graphical assets decomposed into smaller discrete sub-images to be loaded individually by the client on an as-needed basis, and recomposed client-side to form a composite view of part or all of the original image. The W3C RDF Data Cube vocabulary may need enhancing, as it only defines 'slices' rather than 'tilesets'. The tiles and layers are linkable;
3. A layering mechanism to allow placement of tiles above or below other tiles along the 'z' axis (This could also be along the time or any other axis, like wavelength);
4. Properties to define upper and lower bounds of zoom levels for controlling visibility of assets within the viewport.

Some background is at https://github.com/smellman/presentation/blob/master/svgmap.md

W3C SVG 1.2 Alternate content based on display resolutions

SVG 1.2 Working Draft (27 October 2004) had a mechanism to allow higher or lower resolution images, or just a different image at similar resolution, to be displayed instead of the original images. This could be used to provide a tiling mechanism. There is a <multiImage> element with child elements: <subImage> and <subImageRef>. The animation module SMIL is used to provide display control by comparing current pixel size to 'min-pixel-size' and 'max-pixel-size', which may be for separate x and y values for non-square pixels.

W3C SVG2

W3C Scalable Graphics Requirements, published in 1996, list the requirements for a Web-oriented scalable graphics solution. Of these, all are satisfied by SVG except for the Level of Detail requirement. Version 2 of SVG is being developed for 2016. It is basically SVG1.2 compatible, but modularised and with finer control of the interaction between the SVG pictures and their display context, such as HTML5 and CSS3.

No sign of the Tiling and Layering Module.

!W3C RDF Data Cube vocabulary

The RDF DAta Cube does only slices, no other subsets/tiles/partitioning. Slices may have more than one dimension.

Closely related to ISO17369:2013 SDMX (Statistical Data and Metadata eXchange), http://www.dcc.ac.uk/resources/metadata-standards/rdf-data-cube-vocabulary#sthash.X4JyIwQv.dpuf

A data cube has dimensions, attributes and measures, defined in a DataStructureDefinition which has 21 conformance tests.

-- Main.clittle - 13 Aug 2015