Index: trunk/src/board.c
===================================================================
--- trunk/src/board.c	(revision 28922)
+++ trunk/src/board.c	(revision 28923)
@@ -370,6 +370,44 @@
 	return chg;
 }
 
+pcb_coord_t pcb_board_thickness(pcb_board_t *pcb, const char *namespace, pcb_board_thickness_flags_t flags)
+{
+	pcb_layergrp_id_t gid;
+	pcb_layergrp_t *grp;
+	pcb_coord_t curr, total = 0;
+
+	for(gid = 0, grp = pcb->LayerGroups.grp; gid < pcb->LayerGroups.len; gid++,grp++) {
+		const char *s;
+
+		if (!(grp->ltype & PCB_LYT_COPPER) && !(grp->ltype & PCB_LYT_SUBSTRATE))
+			continue;
+
+		if (namespace != NULL)
+			s = pcb_attribute_get_namespace(&grp->Attributes, namespace, "thickness");
+		else
+			s = pcb_attribute_get(&grp->Attributes, "thickness");
+		curr = 0;
+		if (s != NULL)
+			curr = pcb_get_value(s, NULL, NULL, NULL);
+		if (curr <= 0) {
+			if (grp->ltype & PCB_LYT_SUBSTRATE) {
+				if (flags & PCB_BRDTHICK_PRINT_ERROR) {
+					if (namespace != NULL)
+						pcb_message(PCB_MSG_ERROR, "%s: ", namespace);
+					pcb_message(PCB_MSG_ERROR, "can not determine substrate thickness on layer group %ld - total board thickness is probably wrong\n", (long)gid);
+				}
+				if (flags & PCB_BRDTHICK_TOLERANT)
+					continue;
+				return -1;
+			}
+			else
+				continue;
+		}
+		total += curr;
+	}
+	return total;
+}
+
 pcb_pixmap_t *pcb_pixmap_insert_or_free(pcb_board_t *pcb, pcb_pixmap_t *pm)
 {
 	return NULL;
Index: trunk/src/board.h
===================================================================
--- trunk/src/board.h	(revision 28922)
+++ trunk/src/board.h	(revision 28923)
@@ -176,6 +176,16 @@
    board is not a subc, this call is a NOP; implemented in obj_subc.c */
 void pcb_subc_as_board_update(pcb_board_t *pcb);
 
+/*** thickness ***/
+typedef enum pcb_board_thickness_flags_e { /* bitfield */
+	PCB_BRDTHICK_TOLERANT = 1,               /* return -1 if any substrate layer lacks thickness */
+	PCB_BRDTHICK_PRINT_ERROR = 2             /* print an error message for missing thickness attributes */
+} pcb_board_thickness_flags_t;
+
+/* Return the board thickness or -1 on error */
+pcb_coord_t pcb_board_thickness(pcb_board_t *pcb, const char *namespace, pcb_board_thickness_flags_t flags);
+
+
 #define PCB_ACT_BOARD ((pcb_board_t *)argv[0].val.argv0.user_call_ctx)
 
 #endif
Index: trunk/src_plugins/export_gcode/gcode.c
===================================================================
--- trunk/src_plugins/export_gcode/gcode.c	(revision 28922)
+++ trunk/src_plugins/export_gcode/gcode.c	(revision 28923)
@@ -148,34 +148,7 @@
 
 }
 
-static pcb_coord_t pcb_board_thickness(pcb_board_t *pcb)
-{
-	pcb_layergrp_id_t gid;
-	pcb_layergrp_t *grp;
-	pcb_coord_t curr, total = 0;
 
-	for(gid = 0, grp = pcb->LayerGroups.grp; gid < pcb->LayerGroups.len; gid++,grp++) {
-		const char *s;
-
-		if (!(grp->ltype & PCB_LYT_COPPER) && !(grp->ltype & PCB_LYT_SUBSTRATE))
-			continue;
-		s = pcb_attribute_get(&grp->Attributes, "gcode::thickness");
-		if (s == NULL)
-			s = pcb_attribute_get(&grp->Attributes, "thickness");
-
-		curr = 0;
-		if (s != NULL)
-			curr = pcb_get_value(s, NULL, NULL, NULL);
-		if (curr <= 0) {
-			if (grp->ltype & PCB_LYT_SUBSTRATE)
-				pcb_message(PCB_MSG_ERROR, "gcode: can not determine substrate thickness on layer group %ld - total board thickness is probably wrong\n", (long)gid);
-			continue;
-		}
-		total += curr;
-	}
-	return curr;
-}
-
 #define thru_start_depth 102
 
 static void gcode_print_header(void)
@@ -197,7 +170,7 @@
 
 
 	if (total == 0) {
-		total = pcb_board_thickness(gctx.pcb);
+		total = pcb_board_thickness(gctx.pcb, "gcode", PCB_BRDTHICK_PRINT_ERROR);
 		if (total == 0) {
 			pcb_message(PCB_MSG_ERROR, "export_gcode: can't determine board thickness - not exporting thru-cut layer\n");
 			return;
Index: trunk/src_plugins/export_stl/export_stl.c
===================================================================
--- trunk/src_plugins/export_stl/export_stl.c	(revision 28922)
+++ trunk/src_plugins/export_stl/export_stl.c	(revision 28923)
@@ -181,36 +181,6 @@
 	return 0;
 }
 
-TODO("this is the same code as in g-code and probably openscad has a version too - centralize");
-static pcb_coord_t pcb_board_thickness(pcb_board_t *pcb)
-{
-	pcb_layergrp_id_t gid;
-	pcb_layergrp_t *grp;
-	pcb_coord_t curr, total = 0;
-
-	for(gid = 0, grp = pcb->LayerGroups.grp; gid < pcb->LayerGroups.len; gid++,grp++) {
-		const char *s;
-
-		if (!(grp->ltype & PCB_LYT_COPPER) && !(grp->ltype & PCB_LYT_SUBSTRATE))
-			continue;
-		s = pcb_attribute_get(&grp->Attributes, "stl::thickness");
-		if (s == NULL)
-			s = pcb_attribute_get(&grp->Attributes, "thickness");
-
-		curr = 0;
-		if (s != NULL)
-			curr = pcb_get_value(s, NULL, NULL, NULL);
-		if (curr <= 0) {
-			if (grp->ltype & PCB_LYT_SUBSTRATE)
-				pcb_message(PCB_MSG_ERROR, "stl: can not determine substrate thickness on layer group %ld - total board thickness is probably wrong\n", (long)gid);
-			continue;
-		}
-		total += curr;
-	}
-	return curr;
-}
-
-
 static void stl_do_export(pcb_hid_t *hid, pcb_hid_attr_val_t *options)
 {
 	const char *filename;
@@ -240,7 +210,7 @@
 
 	/* determine sheet thickness */
 	if (options[HA_ovrthick].crd > 0) thick = options[HA_ovrthick].crd;
-	else thick = pcb_board_thickness(PCB);
+	else thick = pcb_board_thickness(PCB, "stl", PCB_BRDTHICK_PRINT_ERROR);
 	if (thick <= 0) {
 		pcb_message(PCB_MSG_WARNING, "STL: can not determine board thickness - falling back to hardwired 1.6mm\n");
 		thick = PCB_MM_TO_COORD(1.6);