Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Formalise the ability to use alternative SRS and tiling scheme #11

Merged
merged 2 commits into from
Apr 9, 2020
Merged

Formalise the ability to use alternative SRS and tiling scheme #11

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
7142ed3
Formalise the ability to use alternative SRS and tiling scheme
jtfell Mar 30, 2020
8e1ea82
Add more detail to projection and scheme options
jtfell Apr 9, 2020
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
15 changes: 13 additions & 2 deletions README.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@

Have a question? Discuss the quantized-mesh specification on the [Cesium forum](http://cesiumjs.org/forum.html).

A terrain tileset in quantized-mesh-1.0 format is a simple multi-resolution quadtree pyramid of heightmaps according to the [Tile Map Service (TMS)](http://wiki.osgeo.org/wiki/Tile_Map_Service_Specification) layout and global-geodetic profile. All tiles have the extension .terrain. So, if the Tiles URL for a tileset is:
A terrain tileset in quantized-mesh-1.0 format is a simple multi-resolution quadtree pyramid of heightmaps. All tiles have the extension .terrain. So, if the Tiles URL for a tileset is:

```
http://assets.agi.com/stk-terrain/world/tiles
Expand Down Expand Up @@ -176,6 +176,17 @@ struct EdgeIndices32

These index lists enumerate the vertices that are on the edges of the tile. It is helpful to know which vertices are on the edges in order to add skirts to hide cracks between adjacent levels of detail.

## Tiling Scheme and Coordinate System

By default, the data is tiled according to the [Tile Map Service (TMS)](http://wiki.osgeo.org/wiki/Tile_Map_Service_Specification) layout and global-geodetic system. These defaults can be varied by specifying the `projection` and `scheme`.

Allowed values for the projection are `EPSG:3857` ([Web Mercator](https://en.wikipedia.org/wiki/Web_Mercator_projection) as used by Google Maps) and `EPSG:4326` (Lat/Lng coordinates in the [Global-Geodetic System](https://en.wikipedia.org/wiki/World_Geodetic_System)). It is worth noting that the `EPSG3857` projection has only 1 tile at the root (zoom level 0) while `EPSG:4326` has 2.

The options for the tiling scheme are `tms` and `slippyMap`. The Y coordinates are numbered from the south northwards (eg. latitudes) in the `tms` standard whereas `slippyMap` coordinates have their origin at top left (NW).

For Cesium terrain layers these options can be set in the `layer.json` manifest file. If not specified, they default
to `EPSG:4326` and `tms`.

## Extensions
Extension data may follow to supplement the quantized-mesh with additional information. Each extension begins with an `ExtensionHeader`, consisting of a unique identifier and the size of the extension data in bytes. An `unsigned char` is a 8-bit unsigned integer.

Expand Down Expand Up @@ -271,4 +282,4 @@ struct Metadata
__Requesting:__ For the metadata to be included in the quantized-mesh, the client must request this extension by using the following HTTP Header:
```
Accept : 'application/vnd.quantized-mesh;extensions=metadata'
```
```