4 files changed, 57 insertions, 28 deletions
diff --git a/libcrystfel/src/datatemplate.c b/libcrystfel/src/datatemplate.c
index 4326aa33..290b9227 100644
--- a/libcrystfel/src/datatemplate.c
+++ b/libcrystfel/src/datatemplate.c
@@ -1628,3 +1628,56 @@ int data_template_get_slab_extents(const DataTemplate *dt,
 	*ph = h + 1;
 	return 0;
 }
+
+
+double convert_to_m(double val, int units)
+{
+	switch ( units ) {
+
+		case WAVELENGTH_M :
+		return val;
+
+		case WAVELENGTH_A :
+		return val * 1e-10;
+
+		case WAVELENGTH_PHOTON_EV :
+		return ph_eV_to_lambda(val);
+
+		case WAVELENGTH_PHOTON_KEV :
+		return ph_eV_to_lambda(val*1e3);
+
+		case WAVELENGTH_ELECTRON_V :
+		return el_V_to_lambda(val);
+
+		case WAVELENGTH_ELECTRON_KV :
+		return el_V_to_lambda(val*1e3);
+
+	}
+
+	return NAN;
+}
+
+
+/**
+ * Get the wavelength from a DataTemplate, if possible.
+ *
+ * WARNING: This is probably not the routine you are looking for!
+ *  See the disclaimer for image_create_for_simulation(), which applies
+ *  equally to this routine.
+ *
+ * \returns the wavelength, in metres, or NAN if impossible.
+ */
+double data_template_get_wavelength_if_possible(const DataTemplate *dt)
+{
+	float val;
+	char *rval;
+
+	if ( dt->wavelength_from == NULL ) return NAN;
+
+	val = strtod(dt->wavelength_from, &rval);
+	if ( (*rval == '\0') && (rval != dt->wavelength_from) ) {
+		return convert_to_m(val, dt->wavelength_unit);
+	} else {
+		return NAN;
+	}
+}
diff --git a/libcrystfel/src/datatemplate.h b/libcrystfel/src/datatemplate.h
index 22322b57..3d457f80 100644
--- a/libcrystfel/src/datatemplate.h
+++ b/libcrystfel/src/datatemplate.h
@@ -90,6 +90,8 @@ extern int data_template_get_slab_extents(const DataTemplate *dt, int *pw, int *
 extern struct rg_collection *data_template_get_rigid_groups(const DataTemplate *dtempl,
                                                             const char *collection_name);
 
+extern double data_template_get_wavelength_if_possible(const DataTemplate *dt);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/libcrystfel/src/datatemplate_priv.h b/libcrystfel/src/datatemplate_priv.h
index 62911748..71569273 100644
--- a/libcrystfel/src/datatemplate_priv.h
+++ b/libcrystfel/src/datatemplate_priv.h
@@ -234,4 +234,6 @@ struct _datatemplate
 	char                      *shift_y_from;
 };
 
+extern double convert_to_m(double val, int units);
+
 #endif	/* DATATEMPLATE_PRIV_H */
diff --git a/libcrystfel/src/image.c b/libcrystfel/src/image.c
index 767689f8..db47f75d 100644
--- a/libcrystfel/src/image.c
+++ b/libcrystfel/src/image.c
@@ -400,34 +400,6 @@ static double im_get_length(struct image *image, const char *from,
 }
 
 
-static double convert_to_m(double val, int units)
-{
-	switch ( units ) {
-
-		case WAVELENGTH_M :
-		return val;
-
-		case WAVELENGTH_A :
-		return val * 1e-10;
-
-		case WAVELENGTH_PHOTON_EV :
-		return ph_eV_to_lambda(val);
-
-		case WAVELENGTH_PHOTON_KEV :
-		return ph_eV_to_lambda(val*1e3);
-
-		case WAVELENGTH_ELECTRON_V :
-		return el_V_to_lambda(val);
-
-		case WAVELENGTH_ELECTRON_KV :
-		return el_V_to_lambda(val*1e3);
-
-	}
-
-	return NAN;
-}
-
-
 int create_detgeom(struct image *image, const DataTemplate *dtempl)
 {
 	struct detgeom *detgeom;