Why can I not affect terrain height?

Hey folks. So, I'm trying to learn how to change aspects of Terrain objects in realtime. I've followed [advice][1] from [around][2] the [net][3], but the best information I found came from [this excellent package][4] by @Eric5h5.

I'm temporarily adapting this to work directly with a raycast from the camera, cutting out all the bomb code and just making some magic craters in the terrain...

...or so I intended. In fact, when I click on the terrain, absolutely nothing happens. No terrain changes, and no error messages.

Code follows: using System.Collections; using System.Collections.Generic; using UnityEngine;

 public class PointerV2 : MonoBehaviour
 {
     #region  PointerFields
     private Camera cam;
     private Transform pointObject;
     private Transform hitObject;
 
     private Terrain terrain;
 
     public float rayLength = 128.0f;
     public LayerMask rayMask; // Set to 'Everything'
     #endregion
 
     #region TerraformFields
     [Header("Terraform Fields")]
     public Texture2D crater;            // Alpha channel is used for the shape of the crater
     public float craterDepth = 0.5f;    // Values of less than 1 make crater shallower, with 0 having no effect on the terrain
     private TerrainData terrainData;
     private Color[] craterData;
     #endregion
 
     #region Methods
     private void Awake()
     {
         cam = GetComponent<Camera>();
     }
 
     // Use this for initialization
     void Start()
     {
         hitObject   = GameObject.Find("HitObject").GetComponent<Transform>();
         pointObject = GameObject.Find("PointObject").GetComponent<Transform>();
         terrain     = GameObject.Find("Terrain").GetComponent<Terrain>();
         terrainData = terrain.terrainData;
 
         craterData  = crater.GetPixels();
         for (int i = 0; i < craterData.Length; i++)
         {
             craterData[i].a *= craterDepth;
         }
     }
 
     // Update is called once per frame
     void Update()
     {
         Ray screenRay = cam.ScreenPointToRay(Input.mousePosition);
         RaycastHit rayHit;
         if (Physics.Raycast(screenRay, out rayHit, rayLength, rayMask, QueryTriggerInteraction.Collide))
         {
             Debug.DrawLine(screenRay.origin, rayHit.point, Color.cyan);
         }
         if (rayHit.transform)
         {
             if (rayHit.transform.CompareTag("Terrain"))
             {
                 // Set position of purple sphere
                 pointObject.position = rayHit.point;
 
                 if (Input.GetMouseButtonDown(0))
                 {
                     Crater(rayHit.point.x, rayHit.point.z);
                 }
             }
         }
     }
 
     void Crater(float hitX, float hitZ)
     {
         // Get heightmap coordinates from hit point
         int x = (int)Mathf.Lerp(0, terrainData.heightmapWidth, Mathf.InverseLerp(0, terrainData.size.x, hitX));
         int z = (int)Mathf.Lerp(0, terrainData.heightmapHeight, Mathf.InverseLerp(0, terrainData.size.z, hitZ));
         // Make sure crater area stays within bounds of heightmap
         x = Mathf.Clamp(x, crater.width / 2, terrainData.heightmapWidth - crater.width / 2);
         z = Mathf.Clamp(z, crater.height / 2, terrainData.heightmapHeight - crater.height / 2);
         // Get terrain heightmap data from area surrounding hit point
         var tData = terrainData.GetHeights(x - crater.width / 2, z - crater.height / 2, crater.width, crater.height);
         // Subtract crater from heightmap data
         for (int i = 0; i < crater.height; i++)
         {
             for (int j = 0; j < crater.width; j++)
             {
                 Debug.Log("Writing crater data to tData");
                 tData[i, j] = tData[i, j] - craterData[i * crater.width + j].a; // Can't do "tData -= craterData[]"; generates error
                 // tData[i,j] -= craterData[i * crater.width + j].a;
             }
         }
         // Write modified heightmap data back to the terrain
         terrainData.SetHeights(x - crater.width / 2, z - crater.height / 2, tData);
     }
     #endregion
 }

I'm very new to the process of changing maps during play, and I have great hopes for how I can build shaders to take advantage of these methods. First, though, I need to make some craters...!

Any help, greatly appreciated!

--Rev [1]: https://answers.unity.com/questions/285816/change-terrain-texture-and-tree-at-runtime.html?sort=oldest [2]: https://answers.unity.com/questions/1341730/get-terrain-location-at-raycast-point.html [3]: https://answers.unity.com/questions/9248/how-to-translate-world-coordinates-to-terrain-coor.html [4]: https://forum.unity.com/threads/can-you-realtime-terraform-inside-a-unity-game.10611/#post-75260