Stereo Imagery Extension Specification

• Title: Stereo Imagery
• Identifier: https://stac-extensions.github.io/stereo-imagery/v1.0.0/schema.json
• Field Name Prefix: stereo-img
• Scope: Item, Catalog, Collection
• Extension Maturity Classification: Proposal
• Owner: @m-mohr

This document explains the Stereo Imagery Extension to the SpatioTemporal Asset Catalog (STAC) specification. This extension helps to describe stereo imagery, tri-stereo imagery, etc. This can be any group of 2+ captures with varying viewing angles that allows derive a 3-dimensional view from it. The overlap of the captures should be significantly high (usually 75 % or more) and the time difference between the captures should be minimal (usually a couple of minutes or less).

• Example:
  • Collection: A Collection pointing to a pair of stereo imagery as Items.
  • Item 1: The first Item of the pair.
  • Item 2: The second Item of the pair.
• JSON Schema
• Changelog

Fields

The extension allows to provide the captures as multiple Items.

The field in the table below can be used in these parts of STAC documents:

• Catalogs
• Collections
• Item Properties (incl. Summaries in Collections)

Field Name	Type	Description
stereo-img:count	integer	REQUIRED. The total number of captures in the group. 2 for stereo imagery (minimum), 3 for tri-stereo imagery, etc.
stereo-img:group	string	A unique identifier that for the group of captures. Helps to search for all images of a group.

The field in the table below can be used in these parts of STAC documents:

• Item Properties (incl. Summaries in Collections)
• Links (in Items)

Field Name	Type	Description
stereo-img:number	integer	RECOMMENDED. The capture number in the group, must be > 0 and <= the total count.

The order of the captures that is reflected in stereo-img:number can usually be derived from the acquisition time (datetime) unless there's another specific order for the captures.

It is recommended to provide exact viewing angles, geometries and timestamps for each capture in the Item Properties. Additionally, it is recommended to identify the actual stereo imagery in the assets with the role data.

Relation types

The following types should be used as applicable rel types in the Link Object.

Type	Description
related	Link to the other captures in the group.

If the related relation type is used, it is REQUIRED to provide the stereo-img:number and type fields in the Link Object. This allows clients to distinguish them from other "related" links.

Search Examples

If you'd want to search for distinct stereo imagery groups you could use the API Filter Extension as follows:

• Find one image per pair for stereo-imagery: stereo-img:count = 2 and stereo-img:number = 1 (and then navigate from the first to the other images)
• Only find tri-stereo imagery: stereo-img:count = 3

All examples are expressed in CQL Text.

Contributing

All contributions are subject to the STAC Specification Code of Conduct. For contributions, please follow the STAC specification contributing guide Instructions for running tests are copied here for convenience.

Running tests

The same checks that run as checks on PR's are part of the repository and can be run locally to verify that changes are valid. To run tests locally, you'll need npm, which is a standard part of any node.js installation.

First you'll need to install everything with npm once. Just navigate to the root of this repository and on your command line run:

npm install

Then to check markdown formatting and test the examples against the JSON schema, you can run:

npm test

This will spit out the same texts that you see online, and you can then go and fix your markdown or examples.

If the tests reveal formatting problems with the examples, you can fix them with:

npm run format-examples