From c16c836bd2711357846b5fc55ca14be3dedcfa49 Mon Sep 17 00:00:00 2001
From: Eric Larson <larson.eric.d@gmail.com>
Date: Tue, 3 Jan 2023 13:37:28 -0500
Subject: [PATCH] MAINT: Allow no dig

---
 mne/_fiff/_digitization.py |  3 +++
 mne/coreg.py               | 10 ++++++----
 mne/gui/_coreg.py          | 13 ++++++++-----
 3 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/mne/_fiff/_digitization.py b/mne/_fiff/_digitization.py
index e70a9410af5..c95078f3a3a 100644
--- a/mne/_fiff/_digitization.py
+++ b/mne/_fiff/_digitization.py
@@ -294,6 +294,7 @@ def _get_data_as_dict_from_dig(dig, exclude_ref_channel=True):
     # Split up the dig points by category
     hsp, hpi, elp = list(), list(), list()
     fids, dig_ch_pos_location = dict(), list()
+    dig = [] if dig is None else dig
 
     for d in dig:
         if d["kind"] == FIFF.FIFFV_POINT_CARDINAL:
@@ -308,6 +309,8 @@ def _get_data_as_dict_from_dig(dig, exclude_ref_channel=True):
                 dig_ch_pos_location.append(d["r"])
 
     dig_coord_frames = set([d["coord_frame"] for d in dig])
+    if len(dig_coord_frames) == 0:
+        dig_coord_frames = set([FIFF.FIFFV_COORD_HEAD])
     if len(dig_coord_frames) != 1:
         raise RuntimeError(
             "Only single coordinate frame in dig is supported, "
diff --git a/mne/coreg.py b/mne/coreg.py
index cd9158b7cba..e5de1709cff 100644
--- a/mne/coreg.py
+++ b/mne/coreg.py
@@ -1551,7 +1551,9 @@ def _setup_bem(self):
         low_res_path = _find_head_bem(self._subject, self._subjects_dir, high_res=False)
         if high_res_path is None and low_res_path is None:
             raise RuntimeError(
-                "No standard head model was " f"found for subject {self._subject}"
+                "No standard head model was "
+                f"found for subject {self._subject} in "
+                f"{self._subjects_dir}"
             )
         if high_res_path is not None:
             self._bem_high_res = _read_surface(
@@ -1988,9 +1990,9 @@ def fit_fiducials(
         return self
 
     def _setup_icp(self, n_scale_params):
-        head_pts = list()
-        mri_pts = list()
-        weights = list()
+        head_pts = [np.zeros((0, 3))]
+        mri_pts = [np.zeros((0, 3))]
+        weights = [np.zeros(0)]
         if self._has_dig_data and self._hsp_weight > 0:  # should be true
             head_pts.append(self._filtered_extra_points)
             mri_pts.append(
diff --git a/mne/gui/_coreg.py b/mne/gui/_coreg.py
index c44bd71dd75..6cad5233504 100644
--- a/mne/gui/_coreg.py
+++ b/mne/gui/_coreg.py
@@ -1063,11 +1063,14 @@ def _update_distance_estimation(self):
         )
         dists = self.coreg.compute_dig_mri_distances() * 1e3
         if self._hsp_weight > 0:
-            value += (
-                "\nHSP <-> MRI (mean/min/max): "
-                f"{np.mean(dists):.2f} "
-                f"/ {np.min(dists):.2f} / {np.max(dists):.2f} mm"
-            )
+            if len(dists) == 0:
+                value += "\nNo head shape points found."
+            else:
+                value += (
+                    "\nHSP <-> MRI (mean/min/max): "
+                    f"{np.mean(dists):.2f} "
+                    f"/ {np.min(dists):.2f} / {np.max(dists):.2f} mm"
+                )
         self._forward_widget_command("fit_label", "set_value", value)
 
     def _update_parameters(self):