From 7142ed37275b29b7c256dd876b8b22c7954b0a96 Mon Sep 17 00:00:00 2001 From: Julian Fell Date: Tue, 31 Mar 2020 08:42:09 +1000 Subject: [PATCH 1/2] Formalise the ability to use alternative SRS and tiling scheme --- README.md | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/README.md b/README.md index 2b8f82f..a18fbcc 100644 --- a/README.md +++ b/README.md @@ -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 @@ -176,6 +176,15 @@ 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 profile. These defaults can be varied by specifying the `projection` and `scheme`. + +Allowed values for the projection are `EPSG:3857` and `EPSG:4326` and for the scheme are `tms` and `slippyMap`. + +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. @@ -271,4 +280,4 @@ 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' -``` \ No newline at end of file +``` From 8e1ea82239e8eb7de35caa4e0de15ae99080116a Mon Sep 17 00:00:00 2001 From: Julian Fell Date: Thu, 9 Apr 2020 11:49:33 +1000 Subject: [PATCH 2/2] Add more detail to projection and scheme options --- README.md | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/README.md b/README.md index a18fbcc..63c9eb1 100644 --- a/README.md +++ b/README.md @@ -178,9 +178,11 @@ These index lists enumerate the vertices that are on the edges of the tile. It i ## 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 profile. These defaults can be varied by specifying the `projection` and `scheme`. +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` and `EPSG:4326` and for the scheme are `tms` and `slippyMap`. +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`.