Added sat:anx_start_offset and sat:anx_end_offset fields

stac-extensions · May 22, 2024 · 184187d · 184187d
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - Added `orbit_cycle` field ([#6](https://github.com/stac-extensions/sat/issues/6))
+- Added `sat:anx_start_offset` and `sat:anx_end_offset` fields
 
 ### Changed
 

diff --git a/README.md b/README.md
@@ -21,17 +21,21 @@ It will often be combined with other extensions that describe the actual data, s
 
 ## Item Properties
 
-| Field Name                            | Type    | Description                                                                                                                                                                                             |
-| ------------------------------------- | ------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| sat:platform_international_designator | string  | The International Designator, also known as COSPAR ID, and NSSDCA ID                                                                                                                                    |
-| sat:orbit_state                       | string  | The state of the orbit. Either `ascending` or `descending` for polar orbiting satellites, or `geostationary` for geosynchronous satellites                                                              |
-| sat:absolute_orbit                    | integer | The absolute orbit number at the time of acquisition.                                                                                                                                                   |
-| sat:relative_orbit                    | integer | The relative orbit number at the time of acquisition.                                                                                                                                                   |
-| sat:anx_datetime                      | string  | The [Ascending Node](https://en.wikipedia.org/wiki/Orbital_node) Crossing (ANX) time, in UTC. It is formatted according to [RFC 3339, section 5.6](https://tools.ietf.org/html/rfc3339#section-5.6).    |
+| Field Name                            | Type    | Description                                                  |
+| ------------------------------------- | ------- | ------------------------------------------------------------ |
+| sat:platform_international_designator | string  | The International Designator, also known as COSPAR ID, and NSSDCA ID |
+| sat:orbit_state                       | string  | The state of the orbit. Either `ascending` or `descending` for polar orbiting satellites, or `geostationary` for geosynchronous satellites |
+| sat:absolute_orbit                    | integer | The absolute orbit number at the time of acquisition.        |
+| sat:relative_orbit                    | integer | The relative orbit number at the time of acquisition.        |
 | sat:orbit_cycle                       | integer | The number of repeat cycle done by the satellite at the time of the acquisition. [Repeat cycle](https://ltb.itc.utwente.nl/page/498/concept/81577) is the time between two successive identical orbits. |
+| sat:anx_datetime                      | string  | The [Ascending Node](https://en.wikipedia.org/wiki/Orbital_node) Crossing (ANX) time, in UTC. It is formatted according to [RFC 3339, section 5.6](https://tools.ietf.org/html/rfc3339#section-5.6). |
+| sat:anx_start_offset                  | number  | The time before the satellite reaches the ANX, in seconds. More fine-grained granularity can be expressed through additional decimal places. |
+| sat:anx_end_offset                    | number  | The time after the satellite crosses the ANX, in seconds. More fine-grained granularity can be expressed through additional decimal places. |
 
 *At least one of the fields must be specified.*
 
+`sat:anx_datetime` is required if `sat:anx_start_offset` and/or `sat:anx_end_offset` are provided.
+
 ### Additional Field Information
 
 #### sat:platform_international_designator

diff --git a/json-schema/schema.json b/json-schema/schema.json
@@ -126,21 +126,54 @@
           "type": "integer",
           "minimum": 1
         },
+        "sat:orbit_cycle": {
+          "type": "integer",
+          "minimum": 1
+        },
         "sat:anx_datetime": {
           "type": "string",
           "format": "date-time"
         },
-        "sat:orbit_cycle": {
-          "type": "integer",
-          "minimum": 1
+        "sat:anx_start_offset": {
+          "type": "number",
+          "minimum": 0
+        },
+        "sat:anx_end_offset": {
+          "type": "number",
+          "minimum": 0
         }
       },
       "patternProperties": {
         "^(?!sat:)": {
           "$comment": "Do not allow unspecified fields prefixed with sat:"
         }
       },
-      "additionalProperties": false
+      "additionalProperties": false,
+      "if": {
+        "oneOf": [
+          {
+            "required": [
+              "sat:anx_start_offset"
+            ],
+            "properties": {
+              "sat:anx_start_offset": {}
+            }
+          },
+          {
+            "required": [
+              "sat:anx_end_offset"
+            ],
+            "properties": {
+              "sat:anx_end_offset": {}
+            }
+          }
+        ]
+      },
+      "then": {
+        "required": [
+          "sat:anx_datetime"
+        ]
+      }
     }
   }
 }