instanced-gltf.tsx

import * as React from 'react'
import * as THREE from 'three'
import { useFrame } from '@react-three/fiber'
import { Instance, Instances, useGLTF } from '@react-three/drei'

export default function Tracks() {
  let r = 0

  const { scene } = useGLTF('https://raw.githubusercontent.com/Densyakun/assets/main/railway/track/rail-50n-1067.gltf')

  const instancedMeshesRef = React.useRef<(THREE.InstancedMesh | null)[]>([])

  useFrame(({ }, delta) => {
    r += delta

    instancedMeshesRef.current?.forEach(instancedMesh => instancedMesh && (
      instancedMesh.position.y = Math.sin(r)
    ))
  })

  return (
    <>
      {scene.children.map((child, index) => <Instances
        key={index}
        ref={el => instancedMeshesRef.current[index] = el}
        limit={1000}
        range={30 * 30}
        geometry={(child as THREE.Mesh).geometry}
        material={(child as THREE.Mesh).material}
        receiveShadow
        castShadow
      >
        {[...Array(30)].flatMap((_, z) =>
          [...Array(30)].map((_, x) => <Instance
            key={z * 30 + x}
            position={(child as THREE.Mesh).position.clone().add(new THREE.Vector3(x * 3, 0, z))}
          />)
        )}
      </Instances>)}
    </>
  )
}

not-instanced-gltf.tsx

import * as React from 'react'
import * as THREE from 'three'
import { useFrame } from '@react-three/fiber'
import { Gltf } from '@react-three/drei'

export default function Tracks() {
  let r = 0

  const itemsRef = React.useRef<THREE.Object3D[]>([])

  useFrame(({ }, delta) => {
    const y = Math.sin(r += delta)
    itemsRef.current.forEach(el => el.position.y = y)
  })

  return (
    <>
      {[...Array(30)].flatMap((_, z) =>
        [...Array(30)].map((_, x) => <group ref={(el: THREE.Group) => itemsRef.current[z * 30 + x] = el}>
          <Gltf
            key={z * 30 + x}
            src="https://raw.githubusercontent.com/Densyakun/assets/main/railway/track/rail-50n-1067.gltf"
            position={[x * 3, 0, z]}
            receiveShadow
            castShadow
          />
        </group>)
      )}
    </>
  )
}