Layer densification/munching for map projections

src/execute/mod.rs

@@ -1384,7 +1384,7 @@ pub fn prepare_data_with_reader(query: &str, reader: &dyn Reader) -> Result<Prep
         )?;
     }
     project.apply_projection_transforms(
-        &specs[0].layers,
+        &mut specs[0].layers,
         &mut layer_queries,
         dialect,
         &execute_query,

src/naming.rs

@@ -88,6 +88,11 @@ pub const SOURCE_COLUMN: &str = concatcp!(GGSQL_PREFIX, "source", GGSQL_SUFFIX);
 /// Alias for schema extraction queries
 pub const SCHEMA_ALIAS: &str = concatcp!(GGSQL_SUFFIX, "schema", GGSQL_SUFFIX);
 
+/// Column name for densification group ID.
+/// Used by geoms that expand geometry (tile, segment, ribbon, rule) to group
+/// densified vertices back into their original feature.
+pub const DENSIFY_ID_COLUMN: &str = concatcp!(GGSQL_PREFIX, "densify_id", GGSQL_SUFFIX);
+
 // ============================================================================
 // Constructor Functions
 // ============================================================================

src/plot/layer/geom/line.rs

@@ -3,12 +3,15 @@
 use super::stat_aggregate;
 use super::types::wrap_with_order_by;
 use super::{
-    has_aggregate_param, DefaultAesthetics, DefaultParamValue, GeomTrait, GeomType,
-    ParamConstraint, ParamDefinition, StatResult,
+    densify_edges, has_aggregate_param, needs_projection, project_position_columns,
+    DefaultAesthetics, DefaultParamValue, GeomTrait, GeomType, ParamConstraint, ParamDefinition,
+    StatResult,
 };
 use crate::plot::layer::orientation::{ALIGNED, ORIENTATION_VALUES};
+use crate::plot::projection::Projection;
 use crate::plot::types::DefaultAestheticValue;
-use crate::Mappings;
+use crate::reader::SqlDialect;
+use crate::{naming, Mappings, Result};
 
 /// Line geom - line charts with connected points
 #[derive(Debug, Clone, Copy)]
@@ -77,10 +80,78 @@ impl GeomTrait for Line {
         // the Identity and Aggregate paths.
         Ok(wrap_with_order_by(query, result, "pos1"))
     }
+
+    fn apply_projection(
+        &self,
+        query: &str,
+        projection: &Projection,
+        dialect: &dyn SqlDialect,
+        mappings: &mut Mappings,
+        partition_by: &mut Vec<String>,
+        _parameters: &mut std::collections::HashMap<String, crate::plot::types::ParameterValue>,
+    ) -> Result<String> {
+        if !needs_projection(projection) {
+            return Ok(query.to_string());
+        }
+        let columns = mappings.column_names();
+        let pos1_col = naming::aesthetic_column("pos1");
+        let densified = densify_edges(
+            query,
+            dialect,
+            &columns,
+            partition_by,
+            Some(&pos1_col),
+            false,
+            1.0,
+            360,
+        );
+        project_position_columns(&densified, projection, dialect, &columns)
+    }
 }
 
 impl std::fmt::Display for Line {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         write!(f, "line")
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::plot::types::ParameterValue;
+    use crate::reader::AnsiDialect;
+
+    #[test]
+    fn test_apply_projection_densifies_and_transforms() {
+        let line = Line;
+        let mut projection = Projection::map();
+        projection.properties.insert(
+            "source".to_string(),
+            ParameterValue::String("EPSG:4326".to_string()),
+        );
+        projection.properties.insert(
+            "target".to_string(),
+            ParameterValue::String("+proj=ortho +lat_0=0 +lon_0=0".to_string()),
+        );
+
+        let mut mappings = Mappings::new();
+        mappings.insert_column("pos1", "pos1");
+        mappings.insert_column("pos2", "pos2");
+        let result = line
+            .apply_projection(
+                "SELECT * FROM t",
+                &projection,
+                &AnsiDialect,
+                &mut mappings,
+                &mut vec![],
+                &mut std::collections::HashMap::new(),
+            )
+            .unwrap();
+
+        // Densification happened
+        assert!(result.contains("__ggsql_seq__"));
+        assert!(result.contains("LEAD("));
+        // Projection happened
+        assert!(result.contains("ST_Transform"));
+    }
+}