diff --git a/qpms/scatsystem.h b/qpms/scatsystem.h
index 9cca6f1..9706aac 100644
--- a/qpms/scatsystem.h
+++ b/qpms/scatsystem.h
@@ -11,6 +11,7 @@
 #ifndef QPMS_SCATSYSTEM_H
 #define QPMS_SCATSYSTEM_H
 #include "qpms_types.h"
+#include "vswf.h"
 #include <stdbool.h>
 
 
@@ -319,6 +320,33 @@ complex double *qpms_orbit_irrep_basis(
 		/// The index of the irreducible representation of sym.
 		const qpms_iri_t iri);
 
+
+/// Creates an incident field vector in the full basis, given a function that evaluates the field expansions at points.
+/** TODO detailed doc!
+ * \returns target_full if target_full was not NULL, otherwise the newly allocated array. */
+complex double *qpms_scatsys_incident_field_vector_full(
+		/// Target array. If NULL, a new one is allocated.
+		/** The length of the array is ss->fecv_size. */
+		complex double *target_full,
+		const qpms_scatsys_t *ss,
+		qpms_incfield_t field_at_point,
+		const void *args, ///< Pointer passed as the last argument to (*field_at_point)()
+		bool add ///< If true, add to target_full; rewrite target_full if false.
+		);
+
+/// Creates a (partial) incident field vector in the symmetry-adapted basis, given a function that evaluates the field expansions at points.
+/** TODO detailed doc! */
+complex double *qpms_scatsys_incident_field_vector_irrep_packed(
+		/// Target array. If NULL, a new one is allocated.
+		/** The length of the array is ss->fecv_size. */
+		complex double *target_full,
+		const qpms_scatsys_t *ss,
+		const qpms_iri_t iri, ///< The index of given irreducible representation of ss->sym.
+		qpms_incfield_t field_at_point,
+		const void *args, ///< Pointer passed as the last argument to (*field_at_point)()
+		bool add ///< If true, add to target_full; rewrite target_full if false.
+		);
+
 /// Evaluates scattered fields (corresponding to a given excitation vector) at a given point.
 /**
  * By scattered field, one assumes a linear combination of positive-Hankel-type
@@ -327,7 +355,7 @@ complex double *qpms_orbit_irrep_basis(
  * \return Complex electric field at the point defined by \a where.
  */
 ccart3_t qpms_scatsys_eval_E(const qpms_scatsys_t *ss,
-		const complex double *coeff_vector, ///< A full-length excitation vector.
+		const complex double *coeff_vector, ///< A full-length excitation vector (outgoing wave coefficients).
 		cart3_t where, ///< Evaluation point.
 		complex double k ///< Wave number.
 		);
diff --git a/qpms/vswf.h b/qpms/vswf.h
index 23d1224..f6aff45 100644
--- a/qpms/vswf.h
+++ b/qpms/vswf.h
@@ -11,6 +11,18 @@
 #include "qpms_types.h"
 #include <gsl/gsl_sf_legendre.h>
 
+// -------------- Typedefs (function prototypes) for qpms_vswf_spec_t ----------------------
+
+/// Calculates the (regular VSWF) expansion coefficients of an external incident field.
+typedef qpms_errno_t (*qpms_incfield_t)(
+        /// Target non-NULL array of the regular VSWF expansion coefficients of length bspec->n.
+        complex double *target,
+        const qpms_vswf_set_spec_t *bspec,
+        const cart3_t evalpoint, ///< Point at which the VSWF expansion is made.
+        const void *args, ///< Pointer to additional function-specific arguments.
+        bool add ///< If true, add to target; rewrite target if false.
+);
+
 // ---------------Methods for qpms_vswf_spec_t-----------------------
 //
 /// Creates a qpms_vswf_set_spec_t structure with an empty list of wave indices.
@@ -61,6 +73,33 @@ csphvec_t qpms_eval_uvswf(const qpms_vswf_set_spec_t *setspec,
 		csph_t kr, ///< Evaluation point.
 		qpms_bessel_t btyp);
 
+
+// --- qpms_incfield_t instances and their arguments
+
+typedef struct qpms_incfield_planewane_params_t {
+	bool use_cartesian; ///< If true, wave direction k and amplitude E are specified in cartesian coordinates (via k.cart, E.cart). If false, k is specified in spherical coordinates and E are specified in the corresponding geographical coordinates (via k.sph, E.sph).
+	bool allow_longitudinal; ///< Whether to include longitudinal part or not (if k and E are not orthogonal). Usually false makes sense.
+	union {
+		ccart3_t cart;
+		csph_t sph;
+	} k; ///< Wave vector.
+	union {
+		ccart3_t cart;
+		csphvec_t sph;
+	} E; ///< Electric field amplitude at origin.
+} qpms_incfield_planewave_params_t;
+	
+
+/// Calculates the (regular VSWF) expansion coefficients of a plane wave.
+qpms_errno_t qpms_incfield_planewave(
+        /// Target non-NULL array of the regular VSWF expansion coefficients of length bspec->n.
+        complex double *target,
+        const qpms_vswf_set_spec_t *bspec,
+        const cart3_t evalpoint, ///< Point at which the VSWF expansion is made.
+        const void *args, ///< Pointer to additional function-specific arguments.
+        bool add ///< If true, add to target; rewrite target if false.
+);
+
 // -----------------------------------------------------------------------
 
 /// Electric wave N.