From 7e5c548f918da7747cb8f21d52e3a5ac7f799148 Mon Sep 17 00:00:00 2001
From: Thomas White <taw@physics.org>
Date: Tue, 11 Jul 2023 14:18:37 +0200
Subject: Add detgeom_group_center

---
 libcrystfel/src/detgeom.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++
 libcrystfel/src/detgeom.h |  3 +++
 2 files changed, 61 insertions(+)

diff --git a/libcrystfel/src/detgeom.c b/libcrystfel/src/detgeom.c
index 397edc6a..1e86eb95 100644
--- a/libcrystfel/src/detgeom.c
+++ b/libcrystfel/src/detgeom.c
@@ -264,3 +264,61 @@ gsl_matrix **make_panel_minvs(struct detgeom *dg)
 
 	return Minvs;
 }
+
+
+static void add_point(const struct detgeom_panel *p,
+                      int fs, int ss,
+                      double *tx, double *ty, double *tz)
+{
+	*tx += (p->cnx + fs*p->fsx + ss*p->ssx) * p->pixel_pitch;
+	*ty += (p->cny + fs*p->fsy + ss*p->ssy) * p->pixel_pitch;
+	*tz += (p->cnz + fs*p->fsz + ss*p->ssz) * p->pixel_pitch;
+}
+
+
+int detgeom_group_center(const struct detgeom_panel_group *grp,
+                         double *x, double *y, double *z)
+{
+	if ( grp->n_children == 0 ) {
+
+		const struct detgeom_panel *p = grp->panel;
+		if ( p == NULL ) return 1;
+
+		double tx = 0.0;
+		double ty = 0.0;
+		double tz = 0.0;
+
+		add_point(p, 0, 0, &tx, &ty, &tz);
+		add_point(p, p->w, 0, &tx, &ty, &tz);
+		add_point(p, 0, p->h, &tx, &ty, &tz);
+		add_point(p, p->w, p->h, &tx, &ty, &tz);
+
+		*x = tx / 4.0;
+		*y = ty / 4.0;
+		*z = tz / 4.0;
+
+		return 0;
+
+	} else {
+
+		int i;
+		double tx = 0.0;
+		double ty = 0.0;
+		double tz = 0.0;
+
+		for ( i=0; i<grp->n_children; i++ ) {
+			double gcx, gcy, gcz;
+			detgeom_group_center(grp->children[i], &gcx, &gcy, &gcz);
+			tx += gcx;
+			ty += gcy;
+			tz += gcz;
+		}
+
+		*x = tx / grp->n_children;
+		*y = ty / grp->n_children;
+		*z = tz / grp->n_children;
+
+		return 0;
+
+	}
+}
diff --git a/libcrystfel/src/detgeom.h b/libcrystfel/src/detgeom.h
index 4df67c0c..5a1a758e 100644
--- a/libcrystfel/src/detgeom.h
+++ b/libcrystfel/src/detgeom.h
@@ -143,6 +143,9 @@ extern void detgeom_show_hierarchy(const struct detgeom *dg);
 
 extern void detgeom_translate_detector_m(struct detgeom *dg, double x, double y, double z);
 
+extern int detgeom_group_center(const struct detgeom_panel_group *grp,
+                                double *x, double *y, double *z);
+
 extern gsl_matrix **make_panel_minvs(struct detgeom *dg);
 
 #ifdef __cplusplus
-- 
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