diff --git a/src/msspec/msspecgui/msspec/gui/clusterviewer.py b/src/msspec/msspecgui/msspec/gui/clusterviewer.py
index b1b16b6..52917ad 100644
--- a/src/msspec/msspecgui/msspec/gui/clusterviewer.py
+++ b/src/msspec/msspecgui/msspec/gui/clusterviewer.py
@@ -26,7 +26,7 @@ class ClusterViewer(wx.Window):
     MODE_SELECTION_TOGGLE = 0b0001000
     MODE_TRANSLATION = 0b0010000
     MODE_ROTATION = 0b0100000
-    
+
     def __init__(self, *args, **kwargs):
         kwargs['style'] = wx.NO_FULL_REPAINT_ON_RESIZE | wx.CLIP_CHILDREN
         wx.Window.__init__(self, *args, **kwargs)
@@ -108,7 +108,7 @@ class ClusterViewer(wx.Window):
         This will translate the model to the center of mass, move the model center
         to the center of screen and adjust the scale to the largest dimension of the
         model
-        
+
         :param rescale: if True, the zoom is computed to view the atoms; if False, a fixed zoom value is used
         """
         if atoms is None:
@@ -160,7 +160,7 @@ class ClusterViewer(wx.Window):
         n_mat[0, 0] = n_mat[2, 2] = np.cos(np.radians(ty))
         n_mat[0, 2] = -np.sin(np.radians(ty))
         n_mat[2, 0] = np.sin(np.radians(ty))
-        
+
         self.rotation_matrix = np.dot(m_mat, n_mat)
         self.update_model_matrix()
         self.scale_atoms(self.scale)
@@ -281,7 +281,7 @@ class ClusterViewer(wx.Window):
 
         if self.mode == self.MODE_TRANSLATION:
             self.mode ^= self.MODE_TRANSLATION
-            
+
         self.update_drawing(light=False)
 
     def __evt_right_up_cb(self, event):
@@ -478,7 +478,7 @@ class ClusterViewer(wx.Window):
     def create_background_sprite(self, w, h):
         surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, w, h)
         ctx = cairo.Context(surface)
-        
+
         if True:  # pylint: disable=using-constant-test
             g = cairo.LinearGradient(0, 0, 0, h)
             g.add_color_stop_rgba(0.0, 1.0, 1.0, 1.0, 1.0)
@@ -522,15 +522,15 @@ class ClusterViewer(wx.Window):
             ctx.restore()
 
         self.background_sprite = surface
-    
+
     @classmethod
     def create_v2p_matrix(cls, left, right, bottom, top, near, far):
         """
         creates the matrix that transforms coordinates from view space (space defined by the bounding box passed as argument) to projection space
-        
+
         this transformation is a scale and offset that maps [left; right], [bottom; top], [near; far] to [-1;1], [-1;1], [0;1]
         """
-        v2p_matrix = np.eye(4)
+        v2p_matrix = np.eye(4) * -1
         v2p_matrix[0, 0] = 2. / (right - left)
         v2p_matrix[1, 1] = 2. / (right - left)
         v2p_matrix[2, 2] = 1. / (near - far)
@@ -612,19 +612,23 @@ class ClusterViewer(wx.Window):
         d = 20
         offset = 12
 
-        origin = np.array([0, 0, 0, 1])  # @UnusedVariable
-        x_axis = np.array([d, 0, 0, 1])
-        y_axis = np.array([0, d, 0, 1])
-        z_axis = np.array([0, 0, d, 1])
+        points = np.array([[d, 0, 0, 1, 0],
+                           [0, d, 0, 1, 1],
+                           [0, 0, d, 1, 2]])
 
-        # translation = np.array([[1, 0, 0, d + offset],  # @UnusedVariable
-        #                         [0, 1, 0, h - offset],
-        #                         [0, 0, 1, 1         ],
-        #                         [0, 0, 0, 1         ]])
+        # project onto viewport
+        projections = np.dot(points[:, :4], m_matrix)
+        projections /= projections[:, -1, None]
+        # add the other columns
+        projections = np.c_[projections, points[:, 4:]]
+        # and sort by Z
+        projections = projections[projections[:,2].argsort()[::-1]]
 
         red = (1, 0, 0)
         green = (0, 0.7, 0)
         blue = (0, 0, 1)
+        colors = (red, green, blue)
+        labels = ('X', 'Y', 'Z')
 
         # draw a white circle
         so = np.array([d + offset, h - d - offset, 0])
@@ -637,19 +641,17 @@ class ClusterViewer(wx.Window):
         ctx.set_source_rgba(0.95, 0.95, 0.95, 1)
         ctx.fill()
 
-        for axis, color, label in ((x_axis, red, 'X'),
-                                   (y_axis, green, 'Y'),
-                                   (z_axis, blue, 'Z')):
-            axis = np.dot(axis, m_matrix)
-            axis /= axis[-1]
+        for x, y, z, w, n in projections:
+            n = int(n)
             ctx.move_to(*so[:2])
-            ctx.rel_line_to(*axis[:2])
-            ctx.set_source_rgb(*color)
+            ctx.rel_line_to(x, y)
+            ctx.set_source_rgb(*colors[n])
             ctx.set_line_width(2)
             ctx.set_font_size(10)
-            ctx.show_text(label)
+            ctx.show_text(labels[n])
             ctx.stroke()
 
+
     def render_atoms(self, ctx):
         try:
             atoms = self.atoms
@@ -732,7 +734,7 @@ class ClusterViewer(wx.Window):
                 ctx.set_source_rgb(0, 0, 0)
                 ctx.set_font_size(14)
                 ctx.show_text("%d" % index)
-        
+
         # save the rendering
         self.atoms_sprite = surface
         ctx.set_source_surface(surface, self.im_ox, self.im_oy)
@@ -869,7 +871,7 @@ class ClusterViewer(wx.Window):
 
         #print "scale  = ", self.scale, "scale0 = ", self.scale0
         #self.scale_atoms(1.)
-        
+
         if center:
             self.translate_atoms(w / 2, h / 2)