diff --git a/scilpy/image/datasets.py b/scilpy/image/datasets.py
index 8bdffa93d..ceef9a3ee 100644
--- a/scilpy/image/datasets.py
+++ b/scilpy/image/datasets.py
@@ -74,18 +74,20 @@ def is_voxel_in_bound(self, i, j, k):
 
         Parameters
         ----------
-        i, j, k: ints
-            Voxel indice along each axis.
+        i, j, k: ints or floats
+            Voxel indice along each axis (as ints) or voxel coordinates in
+            voxel world (as floats).
 
         Return
         ------
         out: bool
             True if voxel is in dataset range, False otherwise.
         """
-        return (0 <= i < self.dim[0] and 0 <= j < self.dim[1] and
-                0 <= k < self.dim[2])
+        return (0 <= i <= (self.dim[0] - 1) and
+                0 <= j <= (self.dim[1] - 1) and
+                0 <= k <= (self.dim[2] - 1))
 
-    def voxmm_to_idx(self, x, y, z, origin='center'):
+    def voxmm_to_idx(self, x, y, z, origin):
         """
         Get the 3D indice of the closest voxel at position x, y, z expressed
         in mm.
@@ -95,28 +97,18 @@ def voxmm_to_idx(self, x, y, z, origin='center'):
         x, y, z: floats
             Position coordinate (mm) along x, y, z axis.
         origin: str
-            'Center': Voxel 0,0,0 goes from [-resx/2, -resy/2, -resz/2] to
+            'center': Voxel 0,0,0 goes from [-resx/2, -resy/2, -resz/2] to
                 [resx/2, resy/2, resz/2].
-            'Corner': Voxel 0,0,0 goes from [0,0,0] to [resx, resy, resz].
+            'corner': Voxel 0,0,0 goes from [0,0,0] to [resx, resy, resz].
 
         Return
         ------
         out: list
             3D indice of voxel at position x, y, z.
         """
-        if origin == 'center':
-            return np.asarray([(x + self.voxres[0] / 2) // self.voxres[0],
-                               (y + self.voxres[1] / 2) // self.voxres[1],
-                               (z + self.voxres[2] / 2) // self.voxres[2]],
-                              dtype=int)
-        elif origin == 'corner':
-            return np.asarray([x // self.voxres[0],
-                               y // self.voxres[1],
-                               z // self.voxres[2]], dtype=int)
-        else:
-            raise ValueError("Origin must be one of 'center' or 'corner'.")
+        return np.floor(self.voxmm_to_vox(x, y, z, origin))
 
-    def voxmm_to_vox(self, x, y, z):
+    def voxmm_to_vox(self, x, y, z, origin):
         """
         Get voxel space coordinates at position x, y, z (mm).
 
@@ -124,15 +116,29 @@ def voxmm_to_vox(self, x, y, z):
         ----------
         x, y, z: floats
             Position coordinate (mm) along x, y, z axis.
+        origin: str
+            'center': Voxel 0,0,0 goes from [-resx/2, -resy/2, -resz/2] to
+                [resx/2, resy/2, resz/2].
+            'corner': Voxel 0,0,0 goes from [0,0,0] to [resx, resy, resz].
 
         Return
         ------
         out: list
             Voxel space coordinates for position x, y, z.
         """
-        return [x / self.voxres[0], y / self.voxres[1], z / self.voxres[2]]
+        if origin == 'center':
+            half_res = self.voxres / 2.
+            return [(x + half_res[0]) / self.voxres[0],
+                    (y + half_res[1]) / self.voxres[1],
+                    (z + half_res[2]) / self.voxres[2]]
+        elif origin == 'corner':
+            return [x / self.voxres[0],
+                    y / self.voxres[1],
+                    z / self.voxres[2]]
+        else:
+            raise ValueError("Origin should be 'center' or 'corner'.")
 
-    def voxmm_to_value(self, x, y, z):
+    def voxmm_to_value(self, x, y, z, origin):
         """
         Get the voxel value at voxel position x, y, z (mm) in the dataset.
         If the coordinates are out of bound, the nearest voxel value is taken.
@@ -142,6 +148,10 @@ def voxmm_to_value(self, x, y, z):
         ----------
         x, y, z: floats
             Position coordinate (mm) along x, y, z axis.
+        origin: str
+            'center': Voxel 0,0,0 goes from [-resx/2, -resy/2, -resz/2] to
+                [resx/2, resy/2, resz/2].
+            'corner': Voxel 0,0,0 goes from [0,0,0] to [resx, resy, resz].
 
         Return
         ------
@@ -150,20 +160,42 @@ def voxmm_to_value(self, x, y, z):
             is of length 1, return a scalar value.
         """
         if self.interpolation is not None:
-            if not self.is_voxmm_in_bound(x, y, z):
+            if not self.is_voxmm_in_bound(x, y, z, origin):
                 eps = float(1e-8)  # Epsilon to exclude upper borders
-                x = max(-self.voxres[0] / 2,
-                        min(self.voxres[0] * (self.dim[0] - 0.5 - eps), x))
-                y = max(-self.voxres[1] / 2,
-                        min(self.voxres[1] * (self.dim[1] - 0.5 - eps), y))
-                z = max(-self.voxres[2] / 2,
-                        min(self.voxres[2] * (self.dim[2] - 0.5 - eps), z))
-            coord = np.array(self.voxmm_to_vox(x, y, z), dtype=np.float64)
-
+                if origin == 'corner':
+                    x = max(0,
+                            min(self.voxres[0] * (self.dim[0] - eps), x))
+                    y = max(0,
+                            min(self.voxres[1] * (self.dim[1] - eps), y))
+                    z = max(0,
+                            min(self.voxres[2] * (self.dim[2] - eps), z))
+                elif origin == 'center':
+                    x = max(-self.voxres[0] / 2,
+                            min(self.voxres[0] * (self.dim[0] - 0.5 - eps), x))
+                    y = max(-self.voxres[1] / 2,
+                            min(self.voxres[1] * (self.dim[1] - 0.5 - eps), y))
+                    z = max(-self.voxres[2] / 2,
+                            min(self.voxres[2] * (self.dim[2] - 0.5 - eps), z))
+                else:
+                    raise ValueError("Origin should be 'center' or 'corner'.")
+
+            coord = np.array(self.voxmm_to_vox(x, y, z, origin),
+                             dtype=np.float64)
+
+            # Interpolation: Using dipy's pyx methods. The doc can be found in
+            # the file dipy.core.interpolation.pxd. Dipy works with origin
+            # center.
+            if origin == 'corner':
+                coord -= 0.5
             if self.interpolation == 'nearest':
+                # They use round(point), not floor. This is the equivalent of
+                # origin = 'center'.
                 result = nearestneighbor_interpolate(self.data, coord)
             else:
                 # Trilinear
+                # They do not say it explicitely but they verify if
+                # point[i] < -.5 or point[i] >= (data.shape[i] - .5),
+                # meaning that they work with origin='center'.
                 result = trilinear_interpolate4d(self.data, coord)
 
             # Squeezing returns only value instead of array of length 1 if 3D
@@ -173,7 +205,7 @@ def voxmm_to_value(self, x, y, z):
             raise Exception("No interpolation method was given, cannot run "
                             "this method..")
 
-    def is_voxmm_in_bound(self, x, y, z, origin='center'):
+    def is_voxmm_in_bound(self, x, y, z, origin):
         """
         Test if the position x, y, z mm is in the dataset range.
 
@@ -191,4 +223,4 @@ def is_voxmm_in_bound(self, x, y, z, origin='center'):
         value: bool
             True if position is in dataset range and false otherwise.
         """
-        return self.is_voxel_in_bound(*self.voxmm_to_idx(x, y, z, origin))
+        return self.is_voxel_in_bound(*self.voxmm_to_vox(x, y, z, origin))
diff --git a/scilpy/tracking/propagator.py b/scilpy/tracking/propagator.py
index 768734087..7bff9a106 100644
--- a/scilpy/tracking/propagator.py
+++ b/scilpy/tracking/propagator.py
@@ -9,7 +9,9 @@
 
 class AbstractPropagator(object):
     """
-    Abstract class for tracker object.
+    Abstract class for propagator object. Responsible for sampling the final
+    direction out of the possible directions offered by the tracking field, and
+    for the propagation through Runge-Kutta integration.
 
     Parameters
     ----------
@@ -138,7 +140,7 @@ def propagate(self, pos, v_in):
 
         return new_pos, new_dir, is_direction_valid
 
-    def is_voxmm_in_bound(self, pos, origin='center'):
+    def is_voxmm_in_bound(self, pos, origin):
         """
         Test if the streamline point is inside the boundary of the image.
 
diff --git a/scilpy/tracking/seed.py b/scilpy/tracking/seed.py
index 3a51a77aa..549061590 100644
--- a/scilpy/tracking/seed.py
+++ b/scilpy/tracking/seed.py
@@ -28,6 +28,10 @@ def __init__(self, data, voxres):
         self.data = data
         self.voxres = voxres
 
+        # Everything scilpy.tracking is in 'corner', 'voxmm'
+        self.origin = 'corner'
+        self.space = 'voxmm'
+
         # self.seed are all the voxels where a seed could be placed
         # (voxel space, int numbers).
         self.seeds = np.array(np.where(np.squeeze(data) > 0),
diff --git a/scilpy/tracking/tracker.py b/scilpy/tracking/tracker.py
index 9587c53e7..495216d71 100644
--- a/scilpy/tracking/tracker.py
+++ b/scilpy/tracking/tracker.py
@@ -75,6 +75,10 @@ def __init__(self, propagator: AbstractPropagator, mask: DataVolume,
         self.track_forward_only = track_forward_only
         self.skip = skip
 
+        # Everything scilpy.tracking is in 'corner', 'voxmm'
+        self.origin = 'corner'
+        self.space = 'voxmm'
+
         if self.min_nbr_pts <= 0:
             logging.warning("Minimum number of points cannot be 0. Changed to "
                             "1.")
@@ -164,7 +168,6 @@ def _get_streamlines_sub(self, chunk_id):
         """
         global data_file_info
 
-        # args[0] is the Tracker.
         self.propagator.tracking_field.dataset.data = np.load(
             data_file_info[0], mmap_mode=data_file_info[1])
 
@@ -315,8 +318,10 @@ def _propagate_line(self, is_forward):
             # Bound can be checked with mask or tracking field
             # (through self.propagator.is_voxmm_in_bound)
             propagation_can_continue = (
-                    self.mask.voxmm_to_value(*line[-1]) > 0 and
-                    self.mask.is_voxmm_in_bound(*line[-1], origin='corner'))
+                    self.mask.voxmm_to_value(*line[-1],
+                                             origin=self.origin) > 0 and
+                    self.mask.is_voxmm_in_bound(*line[-1],
+                                                origin=self.origin))
             last_dir = new_dir
 
         if propagation_can_continue:
@@ -328,7 +333,8 @@ def _propagate_line(self, is_forward):
         # Last cleaning of the streamline
         # First position is the seed: necessarily in bound.
         while (len(line) > 1 and
-               not self.propagator.is_voxmm_in_bound(line[-1], 'corner')):
+               not self.propagator.is_voxmm_in_bound(line[-1],
+                                                     origin=self.origin)):
             line.pop()
 
         return line
diff --git a/scilpy/tracking/tracking_field.py b/scilpy/tracking/tracking_field.py
index 97dd6b7d8..28e1027e5 100644
--- a/scilpy/tracking/tracking_field.py
+++ b/scilpy/tracking/tracking_field.py
@@ -30,6 +30,10 @@ def __init__(self, dataset, theta, dipy_sphere=None):
         self.theta = theta
         self.dataset = dataset
 
+        # Everything scilpy.tracking is in 'corner', 'voxmm'
+        self.origin = 'corner'
+        self.space = 'voxmm'
+
         if dipy_sphere:
             if 'symmetric' not in dipy_sphere:
                 raise ValueError('Sphere must be symmetric. Call to '
@@ -175,7 +179,7 @@ def _get_sf(self, pos):
         Parameters
         ----------
         pos: ndarray (3,)
-            Position in mm in the trackable dataset.
+            Position in voxmm in the trackable dataset.
 
         Return
         ------
@@ -183,7 +187,7 @@ def _get_sf(self, pos):
             Spherical function evaluated at pos, normalized by
             its maximum amplitude.
         """
-        sh = self.dataset.voxmm_to_value(*pos)
+        sh = self.dataset.voxmm_to_value(*pos, self.origin)
         sf = np.dot(self.B.T, sh).reshape((-1, 1))
 
         sf_max = np.max(sf)
diff --git a/scripts/scil_compute_local_tracking_dev.py b/scripts/scil_compute_local_tracking_dev.py
index 440953087..2404c84de 100644
--- a/scripts/scil_compute_local_tracking_dev.py
+++ b/scripts/scil_compute_local_tracking_dev.py
@@ -156,6 +156,8 @@ def main():
     seed_res = seed_img.header.get_zooms()[:3]
     seed_generator = SeedGenerator(seed_data, seed_res)
     if args.npv:
+        # toDo. This will not really produce n seeds per voxel, only true
+        #  in average.
         nbr_seeds = len(seed_generator.seeds) * args.npv
     elif args.nt:
         nbr_seeds = args.nt