From fb5e2d7f85547706d436093e86cc289e174f674e Mon Sep 17 00:00:00 2001
From: Alan Morris <akenmorris@gmail.com>
Date: Thu, 5 Feb 2026 12:45:46 -0700
Subject: [PATCH] Resolve #2487 - Auto subset size in grooming should pick a
 smart auto

auto (-1) defaults to a subset of 30 to avoid O(n^2) pairwise ICP on large datasets
---
 Libs/Groom/Groom.cpp    | 2 +-
 Libs/Mesh/MeshUtils.cpp | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/Libs/Groom/Groom.cpp b/Libs/Groom/Groom.cpp
index e5b2a4ac55..0b0f24ab9a 100644
--- a/Libs/Groom/Groom.cpp
+++ b/Libs/Groom/Groom.cpp
@@ -560,7 +560,7 @@ bool Groom::run_alignment() {
   bool any_alignment = false;
 
   int reference_index = -1;
-  int subset_size = -1;
+  int subset_size = base_params.get_alignment_subset_size();
 
   // per-domain alignment
   for (size_t domain = 0; domain < num_domains; domain++) {
diff --git a/Libs/Mesh/MeshUtils.cpp b/Libs/Mesh/MeshUtils.cpp
index 2468230ecb..fdf69958b1 100644
--- a/Libs/Mesh/MeshUtils.cpp
+++ b/Libs/Mesh/MeshUtils.cpp
@@ -182,6 +182,10 @@ PhysicalRegion MeshUtils::boundingBox(const std::vector<Mesh>& meshes, bool cent
 }
 
 int MeshUtils::findReferenceMesh(std::vector<Mesh>& meshes, int random_subset_size) {
+  // auto (-1) defaults to a subset of 30 to avoid O(n^2) pairwise ICP on large datasets
+  if (random_subset_size < 0) {
+    random_subset_size = 30;
+  }
   bool use_random_subset = random_subset_size > 0 && random_subset_size < meshes.size();
   int num_meshes = use_random_subset ? random_subset_size : meshes.size();