3MX file

The 3MX contains general information about the scene, in JSON format. The JSON format was chosen because it is easy to handle and parse by web clients.

A file in 3MX format holds:

3mxVersion – The file’s version number (float number)
name – The scene name (utf-8 string)
description – A description of the scene (utf-8 string).
It can contain HTML tags, but it should not contain new lines.
logo – Logo of the owner of the scene, as a relative path to an image (JPG or PNG).
sceneOptions – A collection of display options for the scene.
layers – One or several layers, containing different types of data. The geometry present in a scene is described in such layers.

The sceneOptions tag is reserved for the displaying application; custom fields can be added to define application-related options.

In the layers collection, each layer has to have an ID and a type. Type-dependent data can be added to a layer description.

Figure 4 shows a schema of the 3MX organization.

3MX scene file format

For now, 3MX declares a single type of layer: meshPyramid. The meshPyramid layer describes a unique 3D textured pyramidal mesh, in the 3MXB form.

Mesh pyramid layer

A layer of type meshPyramid contains the following set of tags:

id		The layer's ID (utf-8 string).
type:	meshPyramid	The layer type.
name		The layer name (utf-8 string).
description		A description of the layer (utf-8 string).
SRS		The spatial reference system (utf-8 string). Only needed for georeferenced data. See also About Spatial reference systems.
SRSOrigin:	[O₀, O₁, O₂]	The model origin, in the specified SRS (array of float32). A point's correct coordinates in the specified SRS are P = P_mesh + SRSOrigin. Optional.
root		The relative path to the root 3MXB file (utf-8 string).

As an example, here is a full 3MX scene file:

{
"3mxVersion": 1,
"name":"Marseille",
"description":"Marseille was generated using InterAtlas‘ oblique imagery system. ",
"logo":"interatlas_logo.png",
"sceneOptions":[{"navigation_mode":"PAN"}],
"layers": 
[
     {
"type":"meshPyramid",
"id":"mesh0",
"name":"Marseille",
"description":"This is a description of the model. It should be between quotation marks.",
"SRS": "EPSG:32631",
"SRSOrigin": [692625,4798280,0],
"root": "Data/Marseille.3mxb"
    }
  ]
}

Using the root contained in the scene layers, the geometry can be loaded, starting with the root 3MXB file.