From d1cad9dcd539acc36fede0f42d8ea70e3ed32070 Mon Sep 17 00:00:00 2001
From: Birk Skyum <birk.skyum@pm.me>
Date: Tue, 5 Nov 2024 02:22:12 +0100
Subject: [PATCH] Make globe a spherical projection

Add projection expression
---
 CHANGELOG.md                             |  3 +-
 src/diff.test.ts                         |  4 +-
 src/reference/v8.json                    | 58 ++++++++++++++++++++----
 src/validate/validate_projection.test.ts |  4 +-
 4 files changed, 55 insertions(+), 14 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e44dee3dd..87625ea77 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,8 +1,7 @@
 ## main
 
 ### ✨ Features and improvements
-- Rename adaptive globe from `globe` to `globe-to-mercator` ([#878](https://github.com/maplibre/maplibre-style-spec/pull/878))
-- Add non-adaptive `globe` ([#878](https://github.com/maplibre/maplibre-style-spec/pull/878))
+- Add projection type expression syntax ([#888](https://github.com/maplibre/maplibre-style-spec/pull/888))
 - _...Add new stuff here..._
 
 ### 🐞 Bug fixes
diff --git a/src/diff.test.ts b/src/diff.test.ts
index a1db3e48a..3a35fdb92 100644
--- a/src/diff.test.ts
+++ b/src/diff.test.ts
@@ -607,10 +607,10 @@ describe('diff', () => {
         } as StyleSpecification,
         {
             projection: {
-                type: 'globe-to-mercator'
+                type: 'globe'
             }
         } as StyleSpecification)).toEqual([
-            {command: 'setProjection', args: [{type: 'globe-to-mercator'}]},
+            {command: 'setProjection', args: [{type: 'globe'}]},
         ]);
     });
 });
diff --git a/src/reference/v8.json b/src/reference/v8.json
index 71129ca02..f983708fe 100644
--- a/src/reference/v8.json
+++ b/src/reference/v8.json
@@ -126,10 +126,55 @@
       }
     },
     "projection": {
-      "type": "projection",
-      "doc": "The projection configuration. **Note:** this definition is still experimental and is under development in maplibre-gl-js.",
-      "example": {
-        "type": "globe-to-mercator"
+      "type": {
+        "type": ["enum", "expression"],
+        "doc": "The projection type. Can be specified as a string, or as an expression for supported projection types.",
+        "default": "mercator",
+        "values": {
+          "mercator": {
+            "doc": "Web Mercator projection.",
+            "expression-compatible": true
+          },
+          "globe": {
+            "doc": "Spherical projection.",
+            "expression-compatible": true
+          },
+          "utm32": {
+            "doc": "Metric central europe.",
+            "expression-compatible": false
+          },
+          "albers": {
+            "doc": "Albers equal-area conic projection.",
+            "expression-compatible": true
+          },
+          "equalEarth": {
+            "doc": "Equal Earth projection.",
+            "expression-compatible": true
+          }
+        },
+        "expression": {
+          "interpolated": true,
+          "parameters": ["zoom"],
+          "validate": "return value.expressionCompatible === true"
+        },
+        "example": {
+          "simple": {
+            "projection": {
+              "type": "albers"
+            }
+          },
+          "expression": {
+            "projection": {
+              "type": [
+                "interpolate",
+                ["linear"],
+                ["zoom"],
+                10, "globe",
+                12, "mercator"
+              ]
+            }
+          }
+        }
       }
     },
     "terrain": {
@@ -4538,7 +4583,7 @@
         ]
       },
       "transition": true,
-      "doc": "How to blend the atmosphere. Where 1 is visible atmosphere and 0 is hidden. It is best to interpolate this expression when using globe-to-mercator projection."
+      "doc": "How to blend the atmosphere. Where 1 is visible atmosphere and 0 is hidden. It is best to interpolate this expression when using globe projection."
     }
   },
   "terrain": {
@@ -4579,9 +4624,6 @@
         },
         "globe": {
           "doc":  "Spherical projection."
-        },
-        "globe-to-mercator": {
-          "doc":  "Spherical projection with zoom transition to Web Mercator projection."
         }
       }
     }
diff --git a/src/validate/validate_projection.test.ts b/src/validate/validate_projection.test.ts
index c872edf0f..a0c02f8a3 100644
--- a/src/validate/validate_projection.test.ts
+++ b/src/validate/validate_projection.test.ts
@@ -26,11 +26,11 @@ describe('Validate projection', () => {
     test('Should return errors according to spec violations', () => {
         const errors = validateProjection({validateSpec, value: {type: 1 as any}, styleSpec: v8, style: {} as any});
         expect(errors).toHaveLength(1);
-        expect(errors[0].message).toBe('type: expected one of [mercator, globe, globe-to-mercator], 1 found');
+        expect(errors[0].message).toBe('type: expected one of [mercator, globe], 1 found');
     });
 
     test('Should pass if everything is according to spec', () => {
-        let errors = validateProjection({validateSpec, value: {type: 'globe-to-mercator'}, styleSpec: v8, style: {} as any});
+        let errors = validateProjection({validateSpec, value: {type: 'globe'}, styleSpec: v8, style: {} as any});
         expect(errors).toHaveLength(0);
         errors = validateProjection({validateSpec, value: {type: 'mercator'}, styleSpec: v8, style: {} as any});
         expect(errors).toHaveLength(0);