diff --git a/src/game.h b/src/game.h
index 1a3f3e2..9f5da08 100644
--- a/src/game.h
+++ b/src/game.h
@@ -2,12 +2,13 @@
 
 #include <glm/glm.hpp>
 using glm::vec3;
+using glm::dvec3;
 
 #include "tangerine.h"
 #include "orbits.h"
 
 
-#define DEFAULT_ORBIT_VERTICES 256
+#define DEFAULT_ORBIT_VERTICES 128
 
 const vec3 DEFAULT_ELLIPSE_COLOR = vec3(0.5, 0.5, 0.5);
 const vec3 SELECTED_ELLIPSE_COLOR = vec3(0.7, 0.2, 0.2);
@@ -69,6 +70,7 @@ struct GameState
 	u32 max_orbits;
 
 	GameOrbit* last_selected_orbit;
+	Entity* coord_overlay;
 };
 
 GameOrbit* getFreeOrbit(GameState* gs);
diff --git a/src/main.cpp b/src/main.cpp
index 1f0acdd..645c2c0 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,6 +1,7 @@
 
 /*
  * TODO:
+ * - add coordinate directions overlay
  * - impulsive orbital maneuvers
  * - replace instances of glm:: with using directives
  * - compile with '-pedantic' and fix macro warnings
@@ -48,6 +49,7 @@ initCamera(RenderState* rs, vec3 cam_pos, vec3 cam_focus, vec3 cam_up)
 	assert(xform_ubo != nullptr);
 	updateGLBuffer(xform_ubo, &rs->camera->xforms);
 }
+
 void
 initLights(RenderState* rs)
 {
@@ -65,6 +67,49 @@ initLights(RenderState* rs)
 	updateGLBuffer(lights_ubo, lb->buffer);
 }
 
+Entity*
+addCoordinateOverlay(RenderState* rs)
+{
+	const u32 num_vertices = 6, num_indicies = 6;
+	Mesh* m = meshInit(rs->assets.arena,
+					num_vertices,
+					num_indicies,
+					false,
+					true);
+
+	m->vertices[0] = vec3(0, 0, 0);
+	m->vertices[1] = vec3(1, 0, 0);
+	m->vertices[2] = vec3(0, 0, 0);
+	m->vertices[3] = vec3(0, 1, 0);
+	m->vertices[4] = vec3(0, 0, 0);
+	m->vertices[5] = vec3(0, 0, 1);
+	u16 indices[num_indicies] = { 0, 1, 2, 3, 4, 5 };
+	memcpy(m->indices, indices, num_indicies * sizeof(*indices));
+	m->colors[0] = vec3(1, 0, 0);
+	m->colors[1] = vec3(1, 0, 0);
+	m->colors[2] = vec3(0, 1, 0);
+	m->colors[3] = vec3(0, 1, 0);
+	m->colors[4] = vec3(0, 0, 1);
+	m->colors[5] = vec3(0, 0, 1);
+
+	Model* mdl = modelInitManual(rs->assets.arena, 1, m);
+	RenderGroup* rg = getRenderGroupByName(rs, "manual mesh group");
+	Entity* e = getFreeEntity(rg);
+	initEntity(e, rs->gl_ctx,
+				rs->rg_arena,
+				mdl,
+				rg->shader->num_vertex_attribs,
+				rg->shader->attrib_mappings,
+				"coordinate overlay",
+				GL_LINES);
+	scaleEntity(e, 5);
+	// TODO: add a gameoverlay that can 'unproject' world coordinates to screen
+	// 	coords
+	setEntityPosition(e, vec3(0, -75 / SCALING + 100, 0));
+
+	return e;
+}
+
 Entity*
 initEllipseEntity(RenderState* rs,
 	const EllipseParameters& ep,
@@ -97,7 +142,7 @@ initEllipseEntity(RenderState* rs,
 				rg->shader->num_vertex_attribs,
 				rg->shader->attrib_mappings,
 				"ellipse 01",
-				GL_LINE_LOOP);
+				GL_LINES);
 
 	return e;
 }
@@ -202,6 +247,8 @@ loadScene(GameState* gs, RenderState* rs)
 	RenderGroup* rg = getFreeRenderGroup(rs);
 	initRenderGroup(rg, rs->rg_arena, shader, 256, "manual mesh group");
 
+	gs->coord_overlay = addCoordinateOverlay(rs);
+
 #if 0
 	double a = 26564.5;		// semi-major axis in km
 	double e = 0.7411;		// eccentricity