Add method to_split in SimpleTilePainter for checking whether to spli…

…t a tile

hips/draw/simple.py

@@ -117,6 +117,34 @@ def _fetch_tiles(self) -> HipsTile:
             tile = HipsTile.fetch(tile_meta, url)
             yield tile
 
+    @staticmethod
+    def _measure_tile_shape(corners: tuple) -> List[list]:
+        """Compute tile edges and diagonals."""
+        x, y = corners
+        edges = []
+        for i in range(len(x)):
+            if i == 3:
+                edges.append(np.sqrt((x[i] - x[0]) ** 2 + (y[i] - y[0]) ** 2))
+            else:
+                edges.append(np.sqrt((x[i + 1] - x[i]) ** 2 + (y[i + 1] - y[i]) ** 2))
+
+        diagonals = []
+        diagonals.append(np.sqrt((x[2] - x[0]) ** 2 + (y[2] - y[0]) ** 2))
+        diagonals.append(np.sqrt((x[3] - x[1]) ** 2 + (y[3] - y[1]) ** 2))
+
+        ratio = float(diagonals[0] / diagonals[1])
+
+        return [edges, diagonals, ratio]
+
+    def to_split(self, meta: HipsTileMeta, wcs: WCSGeometry) -> bool:
+        """Implement tile splitting criteria as mentioned in :ref:`drawing_algo` page."""
+        corners = meta.skycoord_corners.to_pixel(wcs)
+        edges, diagonals, ratio = self._measure_tile_shape(corners)
+
+        return any(i > 300 for i in edges) or \
+               any(i > 150 for i in diagonals) or \
+               ratio < 0.7
+
     @property
     def tiles(self) -> List[HipsTile]:
         """List of `~hips.HipsTile` (cached on multiple access)."""

hips/draw/tests/test_simple.py

@@ -86,6 +86,7 @@ def test_compute_matching_hips_order(self, pars):
             width=2000, height=1000, fov=pars['fov'],
             coordsys='icrs', projection='AIT',
         )
+
         simple_tile_painter = SimpleTilePainter(geometry, self.hips_survey, 'fits')
         assert simple_tile_painter.draw_hips_order == pars['order']
 
@@ -101,3 +102,7 @@ def test_draw_debug_image(self):
         tile = self.painter.tiles[3]
         image = self.painter.image
         plot_mpl_single_tile(self.geometry, tile, image)
+
+    def test_to_split(self):
+        tile = self.painter.tiles[3]
+        assert self.painter.to_split(tile.meta, self.geometry.wcs) == True