Add Blender code to generate viewpoints

lib/poses/predefined_poses/README.md

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+#### Creating viewpoints to generate templates
+
+Download blender
+```
+BLENDER_LIB_PATH=/home/nguyen/Documents/code/blender_lib
+mkdir $BLENDER_LIB_PATH
+curl https://download.blender.org/release/Blender2.82/blender-2.82-linux64.tar.xz -o $BLENDER_LIB_PATH/blender-2.82-linux64.tar.xz
+tar xf $BLENDER_LIB_PATH/blender-2.82-linux64.tar.xz -C $BLENDER_LIB_PATH
+$BLENDER_LIB_PATH/blender-2.82-linux64/blender -b --python ./lib/poses/predefined_poses/create_viewpoints.py
+```
+
+Create viewpoints by subdividing icosphere:
+```
+$BLENDER_LIB_PATH/blender-2.82-linux64/2.82/python/bin/python3.7m ./lib/poses/predefined_poses/create_viewpoints.py
+```

lib/poses/predefined_poses/create_viewpoints.py

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+import bpy
+import bmesh
+import math
+import numpy as np
+import mathutils
+import os
+from math import radians
+
+
+def get_camera_positions(nSubDiv):
+    """
+    * Construct an icosphere
+    * subdived
+    """
+
+    bpy.ops.mesh.primitive_ico_sphere_add(location=(0, 0, 0), enter_editmode=True)
+    # bpy.ops.export_mesh.ply(filepath='./sphere.ply')
+    icos = bpy.context.object
+    me = icos.data
+
+    # -- cut away lower part
+    bm = bmesh.from_edit_mesh(me)
+    sel = [v for v in bm.verts if v.co[2] < 0]
+
+    bmesh.ops.delete(bm, geom=sel, context="FACES")
+    bmesh.update_edit_mesh(me)
+
+    # -- subdivide and move new vertices out to the surface of the sphere
+    #    nSubDiv = 3
+    for i in range(nSubDiv):
+        bpy.ops.mesh.subdivide()
+
+        bm = bmesh.from_edit_mesh(me)
+        for v in bm.verts:
+            l = math.sqrt(v.co[0] ** 2 + v.co[1] ** 2 + v.co[2] ** 2)
+            v.co[0] /= l
+            v.co[1] /= l
+            v.co[2] /= l
+        bmesh.update_edit_mesh(me)
+
+    # -- cut away zero elevation
+    bm = bmesh.from_edit_mesh(me)
+    sel = [v for v in bm.verts if v.co[2] <= 0]
+    bmesh.ops.delete(bm, geom=sel, context="FACES")
+    bmesh.update_edit_mesh(me)
+
+    # convert vertex positions to az,el
+    positions = []
+    angles = []
+    bm = bmesh.from_edit_mesh(me)
+    for v in bm.verts:
+        x = v.co[0]
+        y = v.co[1]
+        z = v.co[2]
+        az = math.atan2(x, y)  # *180./math.pi
+        el = math.atan2(z, math.sqrt(x ** 2 + y ** 2))  # *180./math.pi
+        # positions.append((az,el))
+        angles.append((el, az))
+        positions.append((x, y, z))
+
+    bpy.ops.object.editmode_toggle()
+
+    # sort positions, first by az and el
+    data = zip(angles, positions)
+    positions = sorted(data)
+    positions = [y for x,y in positions]
+    angles = sorted(angles)
+    return angles, positions
+
+
+def convert_location_to_rotation(locations):
+    obj_poses = np.zeros((len(locations), 4, 4))
+    for idx, pt in enumerate(locations):
+        f = -np.array(locations[idx])  # Forward direction.
+        f /= np.linalg.norm(f)
+        u = np.array([0.0, 0.0, 1.0])  # Up direction.
+        s = np.cross(f, u)  # Side direction.
+        if np.count_nonzero(s) == 0:
+            # f and u are parallel, i.e. we are looking along or against Z axis.
+            s = np.array([1.0, 0.0, 0.0])
+        s /= np.linalg.norm(s)
+        u = np.cross(s, f)  # Recompute up.
+        R = np.array([[s[0], s[1], s[2]],
+                      [u[0], u[1], u[2]],
+                      [-f[0], -f[1], -f[2]]])
+        t = pt  # R.dot(np.array(pt).reshape((3, 1)))
+        obj_poses[idx, :3, :3] = R
+        obj_poses[idx, :3, 3] = t.reshape(-1)
+        obj_poses[idx, 3, 3] = 1
+    return obj_poses
+
+# to get predefined poses for level 3
+level = 3
+sphere_level3 = np.load("./lib/poses/predefined_poses/sphere_level3.npy")
+position_icosphere = np.asarray(get_camera_positions(level)[1])
+matrix = convert_location_to_rotation(position_icosphere)
+print(matrix.shape)
+print("Reproducing errors", np.sum(matrix-sphere_level3))