Add cylinder region extension

Author: j9liu

extensions/2.0/Vendor/EXT_implicit_cylinder_region/README.md

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+# EXT_implicit_cylinder_region
+
+## Contributors
+- Sean Lilley, Cesium
+- Janine Liu, Cesium
+
+## Status
+Draft
+
+## Dependencies
+Written against the glTF 2.0 specification.
+
+## Overview
+
+This extension adds an cylinder-based region as an additional shape type to the [`KHR_implicit_shapes`](TODO) extension. Cylinder-based regions are useful for visualizing real-world data that is captured by cylindrical sensors.
+
+`EXT_implicit_cylinder_region` is an extension on the `shape` object in `KHR_implicit_shapes`, where `type` should be set to `"cylinder region"`.
+
+The extension's properties specify a region following the surface of a cylinder between two different radius values. The cylinder does not need to be completely represented by the volume; the region may be hollow inside, like a tube. However, an inner radius of `0` results in a completely solid cylinder volume.
+
+### Details
+
+The cylinder is centered at the origin, where the radius is measured along the `x` and `z` axes. The `height` of the cylinder is aligned with the `y` axis.
+
+<table>
+  <tr>
+    <th>
+    Example
+    </th>
+  </tr>
+  <tr>
+    <td><pre>
+    "extensions": [
+      {
+        "KHR_implicit_shapes": {
+          "shapes": [
+            {
+              "type": "cylinder region",
+              "extensions": {
+                "EXT_implicit_cylinder_region": {
+                  "minRadius": 0.5,
+                  "maxRadius": 1,
+                  "height": 2
+                }
+              }
+            }
+          ]
+        }
+      }
+    ]
+    </pre></td>
+    <td>
+    **TODO** visual example
+    </td>
+  </tr>
+</table>
+
+A cylinder region may also be confined to a specific angular range. The `minAngle` and `maxAngle` properties represent the angles at which the region starts and stops on the cylinder. The cylinder's angular bounds are defined in radians within the range `[-pi, pi]`.
+
+<table>
+  <tr>
+    <th>
+    Example
+    </th>
+  </tr>
+  <tr>
+    <td><pre>
+    "extensions": [
+      {
+        "KHR_implicit_shapes": {
+          "shapes": [
+            {
+              "type": "cylinder region",
+              "extensions": {
+                "EXT_implicit_cylinder_region": {
+                  "minRadius": 0.5,
+                  "maxRadius": 1,
+                  "height": 2,
+                  "minAngle": 0
+                  "maxAngle": 1.5
+                }
+              }
+            }
+          ]
+        }
+      }
+    ]
+    </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_cylinder_region/schema/glTF.KHR_implicit_shapes.shape.EXT_implicit_cylinder_region.schema.json

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+{
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "$id": "glTF.KHR_implicit_shapes.shape.EXT_implicit_cylinder_region.schema.json",
+    "title": "EXT_implicit_cylinder_region extension on KHR_implicit_shapes.shape",
+    "type": "object",
+    "description": "`EXT_implicit_cylinder_region` extension on `KHR_implicit_shapes.shape` to represent an implicit cylinder region in a glTF model.",
+    "allOf": [
+        {
+            "$ref": "glTFProperty.schema.json"
+        }
+    ],
+    "properties": {
+        "minRadius": {
+            "type": "number",
+            "description": "The inner radius of the cylinder region along the X and Z axes, in meters.",
+            "minimum": 0
+        },
+        "maxRadius": {
+            "type": "number",
+            "description": "The outer radius of the cylinder region along the X and Z axes, in meters.",
+            "minimum": 0
+        },
+        "height": {
+            "type": "number",
+            "description": "The height of the cylinder in meters along the Y-axis, in meters.",
+            "minimum": 0
+        },
+        "minAngle": {
+            "type": "number",
+            "description": "The minimum angle of the cylinder region in radians. In other words, this is the angle where the cylinder region starts. Must be in the range [-pi, pi].",
+            "minimum": -3.14159265359,
+            "maximum": 3.14159265359,
+            "default": -3.14159265359
+        },
+        "maxAngle": {
+            "type": "number",
+            "description": "The maximum angle of the cylinder region in radians. In other words, this is the angle where the cylinder region ends. Must be in the range [-pi, pi].",
+            "minimum": -3.14159265359,
+            "maximum": 3.14159265359,
+            "default": 3.14159265359
+        }
+    },
+    "required": [
+        "minRadius",
+        "maxRadius",
+        "height"
+    ]
+}