[Tile-serving] [osm2pgsql-dev/osm2pgsql] Add grouped-linemerge generalization (PR #2482)

[leijurv]

@leijurv commented on this pull request.



> +    // endpoint equality, not ST_Intersects, to avoid deleting unrelated
+    // same-group lines that cross a component. A second pass over the changed
+    // region cleans up outputs of components that disappeared entirely (all
+    // their lines deleted), which leave no reached nodes behind; that pass is
+    // self-correcting because anything it removes either vanished or has a
+    // surviving line in the region and is regenerated below.
+    timer(m_timer_delete).start();
+    auto deleted = dbexec(R"(
+DELETE FROM {dest} d
+ USING _glm_nodes n
+ WHERE {group_join_dn}
+   AND ( (ST_X(ST_StartPoint(d."{geom_column}")) = n.x
+      AND ST_Y(ST_StartPoint(d."{geom_column}")) = n.y)
+     OR (ST_X(ST_EndPoint(d."{geom_column}")) = n.x
+      AND ST_Y(ST_EndPoint(d."{geom_column}")) = n.y) )
+)");

In this first example, A has not changed. But we don't know that: imagine this tile expired for some unrelated reason. The tile to the right has not expired.



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