Remove EXT_implicit_geometry, add EXT_implicit_ellipsoid_region

Author: j9liu

extensions/2.0/Vendor/EXT_implicit_ellipsoid_region/README.md

@@ -0,0 +1,64 @@
+# EXT_implicit_ellipsoid_region
+
+## Contributors
+- Sean Lilley, Cesium
+- Janine Liu, Cesium
+
+## Status
+Draft
+
+## Dependencies
+Written against the glTF 2.0 specification.
+
+## Overview
+
+This extension adds an ellipsoid-based region as an additional shape type to the [`KHR_implicit_shapes`](TODO) extension. Ellipsoid-based regions are commonly used in geospatial applications to describe volumes that conform to the curvature of the Earth, or other bodies.
+
+`EXT_implicit_ellipsoid_region` is an extension on the `shape` object in `KHR_implicit_shapes`, where `type` should be set to `"ellipsoid region"`.
+
+The extension's properties specify a region extruded from the surface of an ellipsoid. The ellipsoid itself is not necessarily part of the volume; it is merely used as reference from which the actual region is defined. However, a region may be extended beneath the surface of the ellipsoid, and thus can possibly contain the entire ellipsoid volume if desired.
+
+### Details
+
+The reference ellipsoid is centered at the origin. The `semiMajorAxisRadius` indicates the radii of the ellipsoid in meters along the `x` and `z` axes. These axes are made equal as a conscious decision to simplify the math implemented for rendering regions.
+
+The `semiMinorAxisRadius` indicates the radius of the ellipsoid in meters along the `y` axis.
+
+The `minHeight` and `maxHeight` properties indicates the heights of the region from the ellipsoid's surface, in meters. The `minimum` height should be lower a value, but not necessarily closer to the surface of the ellipsoid. For example, `maxHeight` may be `10` while `minHeight` is `-100`.
+
+<table>
+  <tr>
+    <th>
+    Example
+    </th>
+  </tr>
+  <tr>
+    <td><pre>
+    "extensions": [
+      {
+        "KHR_implicit_shapes": {
+          "shapes": [
+            {
+              "type": "ellipsoid region",
+              "extensions": {
+                "EXT_implicit_ellipsoid_region": {
+                  "semiMajorAxisRadius": 4,
+                  "semiMinorAxisRadius": 2,
+                  "minHeight": 0,
+                  "maxHeight": 0.5
+                }
+              }
+            }
+          ]
+        }
+      }
+    ]
+    </pre></td>
+    <td>
+    **TODO** visual example
+    </td>
+  </tr>
+</table>
+
+## Optional vs. Required
+This extension is required, meaning it should be placed in both the `extensionsUsed` list and `extensionsRequired` list.

extensions/2.0/Vendor/EXT_implicit_ellipsoid_region/schema/glTF.KHR_implicit_shapes.shape.EXT_implicit_ellipsoid_region.schema.json

@@ -0,0 +1,66 @@
+{
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "$id": "glTF.KHR_implicit_shapes.shape.EXT_implicit_ellipsoid_region.schema.json",
+    "title": "EXT_implicit_ellipsoid_region extension on KHR_implicit_shapes.shape",
+    "type": "object",
+    "description": "`EXT_implicit_ellipsoid_region` extension on `KHR_implicit_shapes.shape` to represent an implicit ellipsoid region in a glTF model. Useful for geospatial applications, such as Earth-conforming voxel data.",
+    "allOf": [
+        {
+            "$ref": "glTFProperty.schema.json"
+        }
+    ],
+    "properties": {
+        "semiMajorAxisRadius": {
+            "type": "number",
+            "description": "The radius along the semi-major axis of the reference ellipsoid in meters. Corresponds to the radii along the X and Z axes.",
+            "minimum": 0
+        },
+        "semiMinorAxisRadius": {
+            "type": "number",
+            "description": "The radius along the semi-minor axis of the reference ellipsoid in meters. Corresponds to the radius along the Y-axis.",
+            "minimum": 0
+        },
+        "minHeight": {
+            "type": "number",
+            "description": "The minimum height of the region relative to the ellipsoid's surface, in meters. May be negative."
+        },
+        "maxHeight": {
+            "type": "number",
+            "description": "The maximum height of the region relative to the ellipsoid's surface, in meters. May be negative."
+        },
+        "minLatitude": {
+            "type": "number",
+            "description": "The minimum latitude (a.k.a. polar angle) of the region, in radians. Must be in the range [-pi/2, pi/2].",
+            "minimum": -1.57079632679,
+            "maximum": 1.57079632679,
+            "default": -1.57079632679
+        },
+        "maxLatitude": {
+            "type": "number",
+            "description": "The maximum latitude (a.k.a. polar angle) of the region, in radians. Must be in the range [-pi/2, pi/2].",
+            "minimum": -1.57079632679,
+            "maximum": 1.57079632679,
+            "default": 1.57079632679
+        },
+        "minLongitude": {
+            "type": "number",
+            "description": "The minimum longitude (a.k.a. azimuthal angle) of the region, in radians. Must be in the range [-pi, pi].",
+            "minimum": -3.14159265359,
+            "maximum": 3.14159265359,
+            "default": -3.14159265359
+        },
+        "maxLongitude": {
+            "type": "number",
+            "description": "The maximum longitude (a.k.a. azimuthal angle) of the region, in radians. Must be in the range [-pi, pi].",
+            "minimum": -3.14159265359,
+            "maximum": 3.14159265359,
+            "default": 3.14159265359
+        }
+    },
+    "required": [
+        "semiMajorAxisRadius",
+        "semiMinorAxisRadius",
+        "minHeight",
+        "maxHeight"
+    ]
+}