diff --git a/src/main.rs b/src/main.rs
index 98645b4..2579b81 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -11,19 +11,41 @@ struct Args {
     /// Name of the output file.
     #[arg(short, long)]
     output: String,
+
+    /// Number of voxels in the x-direction.
+    #[arg(long, default_value_t = 0)]
+    nelx: usize,
+
+    /// Number of voxels in the y-direction.
+    #[arg(long, default_value_t = 0)]
+    nely: usize,
+
+    /// Number of voxels in the z-direction.
+    #[arg(long, default_value_t = 0)]
+    nelz: usize,
 }
 
 fn main() {
     let args = Args::parse();
     let input = if args.input.ends_with(".npy") {
         Spn::from_npy(&args.input)
+    } else if args.input.ends_with(".spn") {
+        if args.nelx < 1 {
+            panic!("Need to specify nelx > 0.")
+        } else if args.nely < 1 {
+            panic!("Need to specify nely > 0.")
+        } else if args.nelz < 1 {
+            panic!("Need to specify nelz > 0.")
+        } else {
+            Spn::new(&args.input, args.nelx, args.nely, args.nelz)
+        }
     } else {
-        panic!("Invalid input {} specified.", args.input)
+        panic!("Invalid input ({}) specified.", args.input)
     };
     let output = if args.output.ends_with(".exo") {
         input.into_exodus()
     } else {
-        panic!("Invalid output {} specified.", args.output)
+        panic!("Invalid output ({}) specified.", args.output)
     };
     output.write(&args.output);
 }
diff --git a/src/spn/mod.rs b/src/spn/mod.rs
index 672e7ab..d5fe08c 100644
--- a/src/spn/mod.rs
+++ b/src/spn/mod.rs
@@ -13,6 +13,8 @@ use std::{
     io::{BufRead, BufReader},
 };
 
+const NODE_NUMBERING_OFFSET: usize = 1;
+
 type SpnData = Array3<u8>;
 type VoxelData<const N: usize> = Vec<[usize; N]>;
 
@@ -88,43 +90,87 @@ fn exodus_data_from_npy_data(
         .iter()
         .map(|entry| {
             vec![
-                entry[2] * nelzplus1 * nelyplus1 + entry[1] * nelzplus1 + entry[0] + 2,
-                entry[2] * nelzplus1 * nelyplus1 + entry[1] * nelzplus1 + entry[0] + 1,
-                entry[2] * nelzplus1 * nelyplus1 + (entry[1] + 1) * nelzplus1 + entry[0] + 1,
-                entry[2] * nelzplus1 * nelyplus1 + (entry[1] + 1) * nelzplus1 + entry[0] + 2,
-                (entry[2] + 1) * nelzplus1 * nelyplus1 + entry[1] * nelzplus1 + entry[0] + 2,
-                (entry[2] + 1) * nelzplus1 * nelyplus1 + entry[1] * nelzplus1 + entry[0] + 1,
-                (entry[2] + 1) * nelzplus1 * nelyplus1 + (entry[1] + 1) * nelzplus1 + entry[0] + 1,
-                (entry[2] + 1) * nelzplus1 * nelyplus1 + (entry[1] + 1) * nelzplus1 + entry[0] + 2,
+                entry[2] * nelzplus1 * nelyplus1
+                    + entry[1] * nelzplus1
+                    + entry[0]
+                    + 1
+                    + NODE_NUMBERING_OFFSET,
+                entry[2] * nelzplus1 * nelyplus1
+                    + entry[1] * nelzplus1
+                    + entry[0]
+                    + NODE_NUMBERING_OFFSET,
+                entry[2] * nelzplus1 * nelyplus1
+                    + (entry[1] + 1) * nelzplus1
+                    + entry[0]
+                    + NODE_NUMBERING_OFFSET,
+                entry[2] * nelzplus1 * nelyplus1
+                    + (entry[1] + 1) * nelzplus1
+                    + entry[0]
+                    + 1
+                    + NODE_NUMBERING_OFFSET,
+                (entry[2] + 1) * nelzplus1 * nelyplus1
+                    + entry[1] * nelzplus1
+                    + entry[0]
+                    + 1
+                    + NODE_NUMBERING_OFFSET,
+                (entry[2] + 1) * nelzplus1 * nelyplus1
+                    + entry[1] * nelzplus1
+                    + entry[0]
+                    + NODE_NUMBERING_OFFSET,
+                (entry[2] + 1) * nelzplus1 * nelyplus1
+                    + (entry[1] + 1) * nelzplus1
+                    + entry[0]
+                    + NODE_NUMBERING_OFFSET,
+                (entry[2] + 1) * nelzplus1 * nelyplus1
+                    + (entry[1] + 1) * nelzplus1
+                    + entry[0]
+                    + 1
+                    + NODE_NUMBERING_OFFSET,
             ]
         })
         .collect();
     element_connectivity_node_renumbering(&mut element_connectivity);
-    let nodal_coordinates = filtered_voxel_data
-        .iter()
-        .map(|entry| {
-            vec![
-                [entry[2], entry[1], entry[0] + 1],
-                [entry[2], entry[1], entry[0]],
-                [entry[2], entry[1] + 1, entry[0]],
-                [entry[2], entry[1] + 1, entry[0] + 1],
-                [entry[2] + 1, entry[1], entry[0] + 1],
-                [entry[2] + 1, entry[1], entry[0]],
-                [entry[2] + 1, entry[1] + 1, entry[0]],
-                [entry[2] + 1, entry[1] + 1, entry[0] + 1],
-            ]
-        })
-        .collect::<Vec<Vec<[usize; 3]>>>()
-        .iter()
+    let number_of_nodes = element_connectivity
+        .clone()
+        .into_iter()
         .flatten()
         .unique()
-        .map(|coordinates| {
-            coordinates
-                .iter()
-                .map(|coordinate| *coordinate as f64)
-                .collect()
-        })
-        .collect();
+        .collect::<Vec<usize>>()
+        .len();
+    let mut nodal_coordinates = vec![vec![0.0; 3]; number_of_nodes];
+    filtered_voxel_data
+        .iter()
+        .zip(element_connectivity.iter())
+        .for_each(|(entry, connectivity)| {
+            nodal_coordinates[connectivity[0] - NODE_NUMBERING_OFFSET] =
+                vec![entry[2] as f64, entry[1] as f64, entry[0] as f64 + 1.0];
+            nodal_coordinates[connectivity[1] - NODE_NUMBERING_OFFSET] =
+                vec![entry[2] as f64, entry[1] as f64, entry[0] as f64];
+            nodal_coordinates[connectivity[2] - NODE_NUMBERING_OFFSET] =
+                vec![entry[2] as f64, entry[1] as f64 + 1.0, entry[0] as f64];
+            nodal_coordinates[connectivity[3] - NODE_NUMBERING_OFFSET] = vec![
+                entry[2] as f64,
+                entry[1] as f64 + 1.0,
+                entry[0] as f64 + 1.0,
+            ];
+            nodal_coordinates[connectivity[4] - NODE_NUMBERING_OFFSET] = vec![
+                entry[2] as f64 + 1.0,
+                entry[1] as f64,
+                entry[0] as f64 + 1.0,
+            ];
+            nodal_coordinates[connectivity[5] - NODE_NUMBERING_OFFSET] =
+                vec![entry[2] as f64 + 1.0, entry[1] as f64, entry[0] as f64];
+            nodal_coordinates[connectivity[6] - NODE_NUMBERING_OFFSET] = vec![
+                entry[2] as f64 + 1.0,
+                entry[1] as f64 + 1.0,
+                entry[0] as f64,
+            ];
+            nodal_coordinates[connectivity[7] - NODE_NUMBERING_OFFSET] = vec![
+                entry[2] as f64 + 1.0,
+                entry[1] as f64 + 1.0,
+                entry[0] as f64 + 1.0,
+            ];
+        });
     (element_blocks, element_connectivity, nodal_coordinates)
 }
 
diff --git a/tests/spn.py b/tests/spn.py
index 9d057f6..234a1f1 100644
--- a/tests/spn.py
+++ b/tests/spn.py
@@ -50,108 +50,108 @@
     [25, 24, 29, 30, 55, 54, 59, 60],
 ])
 gold_coordinates = np.array([
-    [0.0, 0.0, 1.0],
     [0.0, 0.0, 0.0],
+    [0.0, 0.0, 1.0],
+    [0.0, 0.0, 2.0],
+    [0.0, 0.0, 3.0],
+    [0.0, 0.0, 4.0],
     [0.0, 1.0, 0.0],
     [0.0, 1.0, 1.0],
-    [1.0, 0.0, 1.0],
-    [1.0, 0.0, 0.0],
-    [1.0, 1.0, 0.0],
-    [1.0, 1.0, 1.0],
-    [2.0, 0.0, 1.0],
-    [2.0, 0.0, 0.0],
-    [2.0, 1.0, 0.0],
-    [2.0, 1.0, 1.0],
-    [3.0, 0.0, 1.0],
-    [3.0, 0.0, 0.0],
-    [3.0, 1.0, 0.0],
-    [3.0, 1.0, 1.0],
+    [0.0, 1.0, 2.0],
+    [0.0, 1.0, 3.0],
+    [0.0, 1.0, 4.0],
     [0.0, 2.0, 0.0],
     [0.0, 2.0, 1.0],
-    [1.0, 2.0, 0.0],
-    [1.0, 2.0, 1.0],
-    [2.0, 2.0, 0.0],
-    [2.0, 2.0, 1.0],
-    [3.0, 2.0, 0.0],
-    [3.0, 2.0, 1.0],
+    [0.0, 2.0, 2.0],
+    [0.0, 2.0, 3.0],
+    [0.0, 2.0, 4.0],
     [0.0, 3.0, 0.0],
     [0.0, 3.0, 1.0],
-    [1.0, 3.0, 0.0],
-    [1.0, 3.0, 1.0],
-    [2.0, 3.0, 0.0],
-    [2.0, 3.0, 1.0],
-    [3.0, 3.0, 0.0],
-    [3.0, 3.0, 1.0],
+    [0.0, 3.0, 2.0],
+    [0.0, 3.0, 3.0],
+    [0.0, 3.0, 4.0],
     [0.0, 4.0, 0.0],
     [0.0, 4.0, 1.0],
-    [1.0, 4.0, 0.0],
-    [1.0, 4.0, 1.0],
-    [2.0, 4.0, 0.0],
-    [2.0, 4.0, 1.0],
-    [3.0, 4.0, 0.0],
-    [3.0, 4.0, 1.0],
+    [0.0, 4.0, 2.0],
+    [0.0, 4.0, 3.0],
+    [0.0, 4.0, 4.0],
     [0.0, 5.0, 0.0],
     [0.0, 5.0, 1.0],
-    [1.0, 5.0, 0.0],
-    [1.0, 5.0, 1.0],
-    [2.0, 5.0, 0.0],
-    [2.0, 5.0, 1.0],
-    [3.0, 5.0, 0.0],
-    [3.0, 5.0, 1.0],
-    [0.0, 0.0, 2.0],
-    [0.0, 1.0, 2.0],
+    [0.0, 5.0, 2.0],
+    [0.0, 5.0, 3.0],
+    [0.0, 5.0, 4.0],
+    [1.0, 0.0, 0.0],
+    [1.0, 0.0, 1.0],
     [1.0, 0.0, 2.0],
+    [1.0, 0.0, 3.0],
+    [1.0, 0.0, 4.0],
+    [1.0, 1.0, 0.0],
+    [1.0, 1.0, 1.0],
     [1.0, 1.0, 2.0],
-    [2.0, 0.0, 2.0],
-    [2.0, 1.0, 2.0],
-    [3.0, 0.0, 2.0],
-    [3.0, 1.0, 2.0],
-    [0.0, 2.0, 2.0],
+    [1.0, 1.0, 3.0],
+    [1.0, 1.0, 4.0],
+    [1.0, 2.0, 0.0],
+    [1.0, 2.0, 1.0],
     [1.0, 2.0, 2.0],
-    [0.0, 3.0, 2.0],
+    [1.0, 2.0, 3.0],
+    [1.0, 2.0, 4.0],
+    [1.0, 3.0, 0.0],
+    [1.0, 3.0, 1.0],
     [1.0, 3.0, 2.0],
-    [2.0, 2.0, 2.0],
-    [2.0, 3.0, 2.0],
-    [0.0, 4.0, 2.0],
+    [1.0, 3.0, 3.0],
+    [1.0, 3.0, 4.0],
+    [1.0, 4.0, 0.0],
+    [1.0, 4.0, 1.0],
     [1.0, 4.0, 2.0],
-    [0.0, 5.0, 2.0],
+    [1.0, 4.0, 3.0],
+    [1.0, 4.0, 4.0],
+    [1.0, 5.0, 0.0],
+    [1.0, 5.0, 1.0],
     [1.0, 5.0, 2.0],
-    [0.0, 0.0, 3.0],
-    [0.0, 1.0, 3.0],
-    [1.0, 0.0, 3.0],
-    [1.0, 1.0, 3.0],
+    [1.0, 5.0, 3.0],
+    [1.0, 5.0, 4.0],
+    [2.0, 0.0, 0.0],
+    [2.0, 0.0, 1.0],
+    [2.0, 0.0, 2.0],
     [2.0, 0.0, 3.0],
+    [2.0, 0.0, 4.0],
+    [2.0, 1.0, 0.0],
+    [2.0, 1.0, 1.0],
+    [2.0, 1.0, 2.0],
     [2.0, 1.0, 3.0],
-    [3.0, 0.0, 3.0],
-    [3.0, 1.0, 3.0],
-    [0.0, 2.0, 3.0],
-    [1.0, 2.0, 3.0],
-    [0.0, 3.0, 3.0],
-    [1.0, 3.0, 3.0],
+    [2.0, 1.0, 4.0],
+    [2.0, 2.0, 0.0],
+    [2.0, 2.0, 1.0],
+    [2.0, 2.0, 2.0],
     [2.0, 2.0, 3.0],
+    [2.0, 2.0, 4.0],
+    [2.0, 3.0, 0.0],
+    [2.0, 3.0, 1.0],
+    [2.0, 3.0, 2.0],
     [2.0, 3.0, 3.0],
-    [0.0, 4.0, 3.0],
-    [1.0, 4.0, 3.0],
-    [0.0, 5.0, 3.0],
-    [1.0, 5.0, 3.0],
-    [0.0, 0.0, 4.0],
-    [0.0, 1.0, 4.0],
-    [1.0, 0.0, 4.0],
-    [1.0, 1.0, 4.0],
-    [2.0, 0.0, 4.0],
-    [2.0, 1.0, 4.0],
+    [2.0, 3.0, 4.0],
+    [2.0, 4.0, 0.0],
+    [2.0, 4.0, 1.0],
+    [2.0, 5.0, 0.0],
+    [2.0, 5.0, 1.0],
+    [3.0, 0.0, 0.0],
+    [3.0, 0.0, 1.0],
+    [3.0, 0.0, 2.0],
+    [3.0, 0.0, 3.0],
     [3.0, 0.0, 4.0],
+    [3.0, 1.0, 0.0],
+    [3.0, 1.0, 1.0],
+    [3.0, 1.0, 2.0],
+    [3.0, 1.0, 3.0],
     [3.0, 1.0, 4.0],
-    [0.0, 2.0, 4.0],
-    [1.0, 2.0, 4.0],
-    [0.0, 3.0, 4.0],
-    [1.0, 3.0, 4.0],
-    [2.0, 2.0, 4.0],
-    [2.0, 3.0, 4.0],
-    [0.0, 4.0, 4.0],
-    [1.0, 4.0, 4.0],
-    [0.0, 5.0, 4.0],
-    [1.0, 5.0, 4.0],
+    [3.0, 2.0, 0.0],
+    [3.0, 2.0, 1.0],
+    [3.0, 3.0, 0.0],
+    [3.0, 3.0, 1.0],
+    [3.0, 4.0, 0.0],
+    [3.0, 4.0, 1.0],
+    [3.0, 5.0, 0.0],
+    [3.0, 5.0, 1.0],
 ])
 
 
diff --git a/tests/spn.rs b/tests/spn.rs
index 16661b6..d1adbc0 100644
--- a/tests/spn.rs
+++ b/tests/spn.rs
@@ -49,108 +49,108 @@ const GOLD_CONNECTIVITY: [[usize; 8]; NUM_ELEMENTS] = [
     [25, 24, 29, 30, 55, 54, 59, 60],
 ];
 const GOLD_COORDINATES: [[f64; 3]; NUM_NODES] = [
-    [0.0, 0.0, 1.0],
     [0.0, 0.0, 0.0],
+    [0.0, 0.0, 1.0],
+    [0.0, 0.0, 2.0],
+    [0.0, 0.0, 3.0],
+    [0.0, 0.0, 4.0],
     [0.0, 1.0, 0.0],
     [0.0, 1.0, 1.0],
-    [1.0, 0.0, 1.0],
-    [1.0, 0.0, 0.0],
-    [1.0, 1.0, 0.0],
-    [1.0, 1.0, 1.0],
-    [2.0, 0.0, 1.0],
-    [2.0, 0.0, 0.0],
-    [2.0, 1.0, 0.0],
-    [2.0, 1.0, 1.0],
-    [3.0, 0.0, 1.0],
-    [3.0, 0.0, 0.0],
-    [3.0, 1.0, 0.0],
-    [3.0, 1.0, 1.0],
+    [0.0, 1.0, 2.0],
+    [0.0, 1.0, 3.0],
+    [0.0, 1.0, 4.0],
     [0.0, 2.0, 0.0],
     [0.0, 2.0, 1.0],
-    [1.0, 2.0, 0.0],
-    [1.0, 2.0, 1.0],
-    [2.0, 2.0, 0.0],
-    [2.0, 2.0, 1.0],
-    [3.0, 2.0, 0.0],
-    [3.0, 2.0, 1.0],
+    [0.0, 2.0, 2.0],
+    [0.0, 2.0, 3.0],
+    [0.0, 2.0, 4.0],
     [0.0, 3.0, 0.0],
     [0.0, 3.0, 1.0],
-    [1.0, 3.0, 0.0],
-    [1.0, 3.0, 1.0],
-    [2.0, 3.0, 0.0],
-    [2.0, 3.0, 1.0],
-    [3.0, 3.0, 0.0],
-    [3.0, 3.0, 1.0],
+    [0.0, 3.0, 2.0],
+    [0.0, 3.0, 3.0],
+    [0.0, 3.0, 4.0],
     [0.0, 4.0, 0.0],
     [0.0, 4.0, 1.0],
-    [1.0, 4.0, 0.0],
-    [1.0, 4.0, 1.0],
-    [2.0, 4.0, 0.0],
-    [2.0, 4.0, 1.0],
-    [3.0, 4.0, 0.0],
-    [3.0, 4.0, 1.0],
+    [0.0, 4.0, 2.0],
+    [0.0, 4.0, 3.0],
+    [0.0, 4.0, 4.0],
     [0.0, 5.0, 0.0],
     [0.0, 5.0, 1.0],
-    [1.0, 5.0, 0.0],
-    [1.0, 5.0, 1.0],
-    [2.0, 5.0, 0.0],
-    [2.0, 5.0, 1.0],
-    [3.0, 5.0, 0.0],
-    [3.0, 5.0, 1.0],
-    [0.0, 0.0, 2.0],
-    [0.0, 1.0, 2.0],
+    [0.0, 5.0, 2.0],
+    [0.0, 5.0, 3.0],
+    [0.0, 5.0, 4.0],
+    [1.0, 0.0, 0.0],
+    [1.0, 0.0, 1.0],
     [1.0, 0.0, 2.0],
+    [1.0, 0.0, 3.0],
+    [1.0, 0.0, 4.0],
+    [1.0, 1.0, 0.0],
+    [1.0, 1.0, 1.0],
     [1.0, 1.0, 2.0],
-    [2.0, 0.0, 2.0],
-    [2.0, 1.0, 2.0],
-    [3.0, 0.0, 2.0],
-    [3.0, 1.0, 2.0],
-    [0.0, 2.0, 2.0],
+    [1.0, 1.0, 3.0],
+    [1.0, 1.0, 4.0],
+    [1.0, 2.0, 0.0],
+    [1.0, 2.0, 1.0],
     [1.0, 2.0, 2.0],
-    [0.0, 3.0, 2.0],
+    [1.0, 2.0, 3.0],
+    [1.0, 2.0, 4.0],
+    [1.0, 3.0, 0.0],
+    [1.0, 3.0, 1.0],
     [1.0, 3.0, 2.0],
-    [2.0, 2.0, 2.0],
-    [2.0, 3.0, 2.0],
-    [0.0, 4.0, 2.0],
+    [1.0, 3.0, 3.0],
+    [1.0, 3.0, 4.0],
+    [1.0, 4.0, 0.0],
+    [1.0, 4.0, 1.0],
     [1.0, 4.0, 2.0],
-    [0.0, 5.0, 2.0],
+    [1.0, 4.0, 3.0],
+    [1.0, 4.0, 4.0],
+    [1.0, 5.0, 0.0],
+    [1.0, 5.0, 1.0],
     [1.0, 5.0, 2.0],
-    [0.0, 0.0, 3.0],
-    [0.0, 1.0, 3.0],
-    [1.0, 0.0, 3.0],
-    [1.0, 1.0, 3.0],
+    [1.0, 5.0, 3.0],
+    [1.0, 5.0, 4.0],
+    [2.0, 0.0, 0.0],
+    [2.0, 0.0, 1.0],
+    [2.0, 0.0, 2.0],
     [2.0, 0.0, 3.0],
+    [2.0, 0.0, 4.0],
+    [2.0, 1.0, 0.0],
+    [2.0, 1.0, 1.0],
+    [2.0, 1.0, 2.0],
     [2.0, 1.0, 3.0],
-    [3.0, 0.0, 3.0],
-    [3.0, 1.0, 3.0],
-    [0.0, 2.0, 3.0],
-    [1.0, 2.0, 3.0],
-    [0.0, 3.0, 3.0],
-    [1.0, 3.0, 3.0],
+    [2.0, 1.0, 4.0],
+    [2.0, 2.0, 0.0],
+    [2.0, 2.0, 1.0],
+    [2.0, 2.0, 2.0],
     [2.0, 2.0, 3.0],
+    [2.0, 2.0, 4.0],
+    [2.0, 3.0, 0.0],
+    [2.0, 3.0, 1.0],
+    [2.0, 3.0, 2.0],
     [2.0, 3.0, 3.0],
-    [0.0, 4.0, 3.0],
-    [1.0, 4.0, 3.0],
-    [0.0, 5.0, 3.0],
-    [1.0, 5.0, 3.0],
-    [0.0, 0.0, 4.0],
-    [0.0, 1.0, 4.0],
-    [1.0, 0.0, 4.0],
-    [1.0, 1.0, 4.0],
-    [2.0, 0.0, 4.0],
-    [2.0, 1.0, 4.0],
+    [2.0, 3.0, 4.0],
+    [2.0, 4.0, 0.0],
+    [2.0, 4.0, 1.0],
+    [2.0, 5.0, 0.0],
+    [2.0, 5.0, 1.0],
+    [3.0, 0.0, 0.0],
+    [3.0, 0.0, 1.0],
+    [3.0, 0.0, 2.0],
+    [3.0, 0.0, 3.0],
     [3.0, 0.0, 4.0],
+    [3.0, 1.0, 0.0],
+    [3.0, 1.0, 1.0],
+    [3.0, 1.0, 2.0],
+    [3.0, 1.0, 3.0],
     [3.0, 1.0, 4.0],
-    [0.0, 2.0, 4.0],
-    [1.0, 2.0, 4.0],
-    [0.0, 3.0, 4.0],
-    [1.0, 3.0, 4.0],
-    [2.0, 2.0, 4.0],
-    [2.0, 3.0, 4.0],
-    [0.0, 4.0, 4.0],
-    [1.0, 4.0, 4.0],
-    [0.0, 5.0, 4.0],
-    [1.0, 5.0, 4.0],
+    [3.0, 2.0, 0.0],
+    [3.0, 2.0, 1.0],
+    [3.0, 3.0, 0.0],
+    [3.0, 3.0, 1.0],
+    [3.0, 4.0, 0.0],
+    [3.0, 4.0, 1.0],
+    [3.0, 5.0, 0.0],
+    [3.0, 5.0, 1.0],
 ];
 const GOLD_DATA: [[[u8; NELX]; NELY]; NELZ] = [
     [[1, 1, 1], [1, 1, 1], [1, 1, 1], [1, 1, 1], [1, 1, 1]],