Index: trunk/src/layer_grp.c
===================================================================
--- trunk/src/layer_grp.c	(revision 8647)
+++ trunk/src/layer_grp.c	(revision 8648)
@@ -54,6 +54,13 @@
 	inhibit_notify--;
 }
 
+pcb_layergrp_id_t pcb_layergrp_id(pcb_board_t *pcb, pcb_layer_group_t *grp)
+{
+	if ((grp >= &pcb->LayerGroups.grp[0]) && (grp < &pcb->LayerGroups.grp[pcb->LayerGroups.len]))
+		return grp - &pcb->LayerGroups.grp[0];
+	return -1;
+}
+
 pcb_layergrp_id_t pcb_layer_get_group_(pcb_layer_t *Layer)
 {
 	return Layer->grp;
Index: trunk/src/layer_grp.h
===================================================================
--- trunk/src/layer_grp.h	(revision 8647)
+++ trunk/src/layer_grp.h	(revision 8648)
@@ -61,6 +61,10 @@
 /* Return the layer group for an id, or NULL on error (range check) */
 pcb_layer_group_t *pcb_get_layergrp(pcb_board_t *pcb, pcb_layergrp_id_t gid);
 
+/* Return the gid if grp is in the stackup of pcb (else return -1) */
+pcb_layergrp_id_t pcb_layergrp_id(pcb_board_t *pcb, pcb_layer_group_t *grp);
+
+
 /* lookup the group to which a layer belongs to returns -1 if no group is found */
 pcb_layergrp_id_t pcb_layer_get_group(pcb_board_t *pcb, pcb_layer_id_t Layer);
 pcb_layergrp_id_t pcb_layer_get_group_(pcb_layer_t *Layer);