From c8a64ff5e9df3e1887545125697334812e1749ef Mon Sep 17 00:00:00 2001 From: Matt McCormick Date: Tue, 20 Jan 2026 09:57:47 -0500 Subject: [PATCH] rfc4: clarify coordinate direction convention anterior-to-posterior is from negative to positive along the axis. negative to positive along the axis is defined by its spatial metadata. Requested: https://forum.image.sc/t/rfc-4-updates-enhanced-anatomical-orientation-support-for-ome-ngff/115625/6 --- rfc/4/index.md | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/rfc/4/index.md b/rfc/4/index.md index 95543104..80347dfa 100644 --- a/rfc/4/index.md +++ b/rfc/4/index.md @@ -77,6 +77,16 @@ This metadata MUST only be used in cases where there is a single subject in the The `orientation` field is structured as an object and MUST have a `type` field that specifies the orientation domain (e.g., "anatomical") and MUST have a `value` field that specifies the specific orientation within that domain. Valid `type` strings are defined in this document -- currently only `"anatomical"`. +### Coordinate Direction Convention + +The directional orientation values (e.g., "anterior-to-posterior", "left-to-right") specify the direction from negative to positive coordinates along the axis. For example, an axis with `"orientation": {"type": "anatomical", "value": "anterior-to-posterior"}` indicates that: + +- Coordinate values increase from the anterior (front) toward the posterior (back) +- The most anterior position has the smallest coordinate value +- The most posterior position has the largest coordinate value + +This convention aligns with the axis coordinate system defined by the spatial metadata specified elsewhere in the NGFF specification. The `orientation` field provides semantic meaning to the coordinate direction already established by these spatial transforms. + ### Example For anatomical data, an example axis configuration would look like: @@ -484,3 +494,4 @@ End-user applications SHOULD display the encoded information with, for example, | 2025-07-17 | Updated field name from `anatomicalOrientation` to `orientation` with structured `type`/`value` approach to support extensibility to other orientation domains. | [https://github.com/ome/ngff/pull/318](https://github.com/ome/ngff/pull/318) | | 2025-07-23 | Clarify that the type fields are MUST's and the only currently defined value is "anatomical". | [https://github.com/ome/ngff/pull/329](https://github.com/ome/ngff/pull/329) | | 2025-07-23 | Use a Pydantic Literal for anatomical type | [https://github.com/ome/ngff/pull/330](https://github.com/ome/ngff/pull/330) | +| 2026-01-20 | Clarify coordinate direction convention | [https://github.com/ome/ngff/pull/428](https://github.com/ome/ngff/pull/428) |