3 files changed, 40 insertions, 7 deletions
diff --git a/libcrystfel/src/geometry.c b/libcrystfel/src/geometry.c
index beae9a16..ff5cea4d 100644
--- a/libcrystfel/src/geometry.c
+++ b/libcrystfel/src/geometry.c
@@ -245,7 +245,7 @@ static Reflection *check_reflection(struct image *image, Crystal *cryst,
 {
 	Reflection *refl;
 	double R, top;
-	double kmin, kmax, k0, knom, k1;
+	double kmin, kmax, k0, knom, k1, khalf;
 	double dcs, exerr;
 
 	/* Don't predict 000 */
@@ -256,6 +256,7 @@ static Reflection *check_reflection(struct image *image, Crystal *cryst,
 	R = crystal_get_profile_radius(cryst);
 	top = R*R - xl*xl - yl*yl - zl*zl;
 	k0 = top/(2.0*(zl+R));
+	khalf = (- xl*xl - yl*yl - zl*zl) / (2.0*zl);
 	k1 = top/(2.0*(zl-R));
 
 	/* The reflection is excited if any of the reflection is within 2sigma
@@ -306,6 +307,7 @@ static Reflection *check_reflection(struct image *image, Crystal *cryst,
 	}
 
 	set_kpred(refl, knom);
+	set_khalf(refl, khalf);
 	set_exerr(refl, exerr);
 	set_lorentz(refl, 1.0);
 	set_symmetric_indices(refl, h, k, l);
diff --git a/libcrystfel/src/reflist.c b/libcrystfel/src/reflist.c
index 69fb29be..a35aa575 100644
--- a/libcrystfel/src/reflist.c
+++ b/libcrystfel/src/reflist.c
@@ -67,7 +67,8 @@ struct _refldata {
 	signed int ls;
 
 	/* Partiality and related geometrical stuff */
-	double kpred; /* Wavenumber of middle of reflection */
+	double khalf; /* Wavenumber of middle of reflection */
+	double kpred; /* Wavenumber for prediction */
 	double exerr; /* Excitation error */
 	double p;     /* Partiality */
 	double L;     /* Lorentz factor */
@@ -422,12 +423,27 @@ double get_intensity(const Reflection *refl)
 
 
 /**
- * get_kpred:
+ * get_khalf
  * @refl: A %Reflection
  *
  * Returns: the wavenumber at the centre of the reflection
  *
  **/
+double get_khalf(const Reflection *refl)
+{
+	return refl->data.khalf;
+}
+
+
+
+
+/**
+ * get_kpred:
+ * @refl: A %Reflection
+ *
+ * Returns: the wavenumber which should be used for prediction of this reflection
+ *
+ **/
 double get_kpred(const Reflection *refl)
 {
 	return refl->data.kpred;
@@ -618,14 +634,27 @@ void set_panel(Reflection *refl, struct panel *p)
 	refl->data.panel = p;
 }
 
+/**
+ * set_khalf:
+ * @refl: A %Reflection
+ * @khalf: The wavenumber at which the reflection should be predicted
+ *
+ * Sets the wavenumber at the centre of the reflection.
+ **/
+void set_khalf(Reflection *refl, double khalf)
+{
+	refl->data.khalf = khalf;
+}
+
+
 
 /**
  * set_kpred:
  * @refl: A %Reflection
  * @kpred: The wavenumber at which the reflection should be predicted
  *
- * Sets the wavenumber at the centre of the reflection.  Used by
- * predict_to_res() and update_predictions()
+ * Sets the wavenumber at which the reflection should be predicted.
+ * Used by predict_to_res() and update_predictions()
  **/
 void set_kpred(Reflection *refl, double kpred)
 {
diff --git a/libcrystfel/src/reflist.h b/libcrystfel/src/reflist.h
index 4dd1e56f..9f494474 100644
--- a/libcrystfel/src/reflist.h
+++ b/libcrystfel/src/reflist.h
@@ -3,11 +3,11 @@
  *
  * Fast reflection/peak list
  *
- * Copyright © 2012-2016 Deutsches Elektronen-Synchrotron DESY,
+ * Copyright © 2012-2017 Deutsches Elektronen-Synchrotron DESY,
  *                       a research centre of the Helmholtz Association.
  *
  * Authors:
- *   2011-2016 Thomas White <taw@physics.org>
+ *   2011-2017 Thomas White <taw@physics.org>
  *
  * This file is part of CrystFEL.
  *
@@ -87,6 +87,7 @@ extern Reflection *next_found_refl(Reflection *refl);
 extern void get_detector_pos(const Reflection *refl, double *fs, double *ss);
 extern struct panel *get_panel(const Reflection *refl);
 extern double get_partiality(const Reflection *refl);
+extern double get_khalf(const Reflection *refl);
 extern double get_kpred(const Reflection *refl);
 extern double get_exerr(const Reflection *refl);
 extern double get_lorentz(const Reflection *refl);
@@ -110,6 +111,7 @@ extern void copy_data(Reflection *to, const Reflection *from);
 extern void set_detector_pos(Reflection *refl, double fs, double ss);
 extern void set_panel(Reflection *refl, struct panel *p);
 extern void set_kpred(Reflection *refl, double kpred);
+extern void set_khalf(Reflection *refl, double khalf);
 extern void set_exerr(Reflection *refl, double exerr);
 extern void set_partiality(Reflection *refl, double p);
 extern void set_lorentz(Reflection *refl, double L);