VSP + A*

VegetationSplatmapGenerator.cs

using System.Collections;
using System.Collections.Generic;
using AwesomeTechnologies.Vegetation;
using AwesomeTechnologies.VegetationSystem;
using AwesomeTechnologies.Vegetation.Masks;
using AwesomeTechnologies.ColliderSystem;
using Sirenix.OdinInspector;
using UnityEngine;
using System;
using System.IO;

[System.Serializable]
public class VegetationSplatmapLayer : System.Object
{
    public int layer;
    public float penalty;
}

public class VegetationSplatmapGenerator : MonoBehaviour
{
    public Terrain terrain;
    public int size = 512;
    public List<VegetationSplatmapLayer> layers = new List<VegetationSplatmapLayer>();

    public Texture2D obstacleTexture;

    public string targetFile;

    [ContextMenu("Save Vegetation Splatmap")]
    void SaveVegetationSplatmap()
    {
        Dictionary<int, float> penalties = new Dictionary<int, float>();
        foreach (var item in layers)
        {
            penalties.Add(item.layer, item.penalty);
        }

        float[,,] maps = terrain.terrainData.GetAlphamaps(0, 0, terrain.terrainData.alphamapWidth, terrain.terrainData.alphamapHeight);

        int patches = terrain.terrainData.alphamapHeight / size;

        Texture2D texture = new Texture2D(size, size, TextureFormat.ARGB32, false, true);

        for (int y = 0; y < size; y++)
        {
            for (int x = 0; x < size; x++)
            {
                float layerValue = 0;
                int layerIndex = 0;

                for (int z = 0; z < terrain.terrainData.alphamapLayers; z++)
                {
                    if (maps[x * patches, y * patches, z] > layerValue)
                    {
                        layerValue = maps[x * patches, y * patches, z];
                        layerIndex = z;
                    }
                }

                float color = 1;

                if (penalties.ContainsKey(layerIndex))
                {
                    color = penalties[layerIndex];
                }

                if (obstacleTexture != null)
                {
                    texture.SetPixel(y, x, new Color(obstacleTexture.GetPixel(y, x).r, color, 0));
                }
                else
                {
                    texture.SetPixel(y, x, new Color(0, color, 0));
                }
            }
        }

        texture.Apply();

        byte[] data = texture.EncodeToPNG();
        string targetPath = Path.Combine(Application.dataPath, targetFile);
        System.IO.File.WriteAllBytes(targetPath, data);

        Debug.Log(targetPath + " was saved.");
    }
}