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python-ue4-metahuman-nerf：我创造了一个数字人！！_ue4-nerf

作者：2023面试高手 | 2024-02-15 09:14:06

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原文：https://zhuanlan.zhihu.com/p/561152870

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1. 准备工作：制作 MetaHuman 角色

1.1 创建 MetaHuman 角色

1.2 Quixel Bridge 下载 MetaHuman

1.3 导出 MetaHuman 到 UE4

2. UE 渲染 MetaHuman 的多视点图片

2.1 如何在 UE 中手动渲染视频？

2.2 Python 自动化渲染

2.3 全部代码

3. 渲染结果

随着 ECCV 2020 NeRF 的出现，在计算机视觉、计算机图形学、三维重建等领域砸开了无数的坑位，一篇 NeRF 养活了多少科研工作者、大厂员工。但是要想训练这样一个 Neural Radiance Filed 却不是一件容易的事情，首先从数据来看，训练一个 NeRF 需要该场景的多视点图片，同时还需要知道每张图片所对应的相机参数，要想得到这样的数据，可谓是耗时耗力。那么，有没有一种方式，可以虚拟的仿真出一组 NeRF 的训练数据？

答案当然是有的，而且不止一种方式。下面本文将分享一种使用 UE4 来渲染带有相机参数的多视点图片的方法。在正式开始之前，首先来介绍一下 MetaHuman，它就是我们要渲染的对象。在计算机视觉、三维重建领域，人脸方向的研究一直是一个热点，而 MetaHuman 则是一个高保真的数字人开源框架，我们可以利用 MetaHuman 来设计出自己想要的数字人形象，然后渲染出其多视点图片，用作进一步的研究。

1. 准备工作：制作 MetaHuman 角色

在 UE4 中渲染 MetaHuman 之前，我们首先需要创造一个 Metahuman 角色，然后并将其导入到 UE4 中进行渲染，整体可分为以下几个步骤

使用 MetaHuman Creator 创建 MetaHuman 角色；也可以不创建新角色，直接使用自带的即可。
借助 Quixel Bridge 工具将创建的 MetaHuman 角色下载下来。
在 Quixel Bridge 中将 MetaHuman 角色导出到 UE4中。

下面分别对这几步进行说明：

1.1 创建 MetaHuman 角色

登入 MetaHuman Creator 官网：https://metahuman.unrealengine.com/，会看到如下界面，左侧的 CREATE METAHUMAN 是系统默认给出的 Metahuman 角色，可以直接在其基础上进行修改，创作一个新的 Metahuman，这会存在左侧的 MY METAHUMAN 目录中。

具体的操作界面如下，整体分为三部分：脸部、毛发、身体。我们可以对这三部分中的各个细节进行操作，大家可以自行尝试~

1.2 Quixel Bridge 下载 MetaHuman

我们刚刚创作好的 MetaHuman 角色是存在于官方的服务器上的，在对它进行操作之前，还需要借助 Quixel Bridge 工具将其下载下来。

Quixel Bridge 下载链接：https://quixel.com/bridge

在下载时候，我们使用 Epic Games 账号，后续用的也一直是这个账号。下载完成并登录之后，我们会看到如下界面

左侧导航栏中的 MetaHuman Presets 和 My MetaHuman 分别表示默认角色和我们前一步创建的角色。点击右上角绿色的下载按钮即可下载到本地。

1.3 导出 MetaHuman 到 UE4

在导出 MetaHuman 角色到 UE4 之前，我们需要配置：导出的目标引擎是什么、引擎的版本号、引擎的位置。如下图所示

之后，点击对应 MetaHuman 角色右上角的 Export 按钮即可将其导出到 UE 引擎中（注意：在导出时，要保证 UE 是打开的）。

2. UE 渲染 MetaHuman 的多视点图片

在利用 Python 自动化渲染符合要求的多视点图片之前，我们首先要搞明白的一件事情是：如何手动的在 UE4 中渲染视频序列（视频和图片本质上是一样的，图片就是视频一帧一帧截出来的）？

2.1 如何在 UE 中手动渲染视频？

step1：将 MetaHuman 导入到 UE4 的场景中，并将其定位到合适的位置。在场景中添加电影摄像机 CineCameraActor，如下：

step2：创建过场动画，并添加关卡序列，如下

step3：依次点击，轨道 — Actor到Sequencer — CineCameraActor，创建 CineCameraActor 的轨道序列，如下

step4：在创建好的 CineCameraActor 轨道序列中添加关键帧（下图添加了 5 个关键帧，分别指定了相机的位置和旋转），使得相机按照既定方式运动，如下

step5：至此，视频序列创建完毕，点击 将影片渲染为视频序列或图片序列，完成导出

上述就是在 UE4 中渲染 MetaHuman 的整个过程，只需要鼠标点点就行了，比较简单。但是有一个严重的问题是：如果要渲染一个多视点 MetaHuman 数据集用作 NeRF 训练的话，我们是必须要知道相机的姿态的；而在上述过程中，我们只能准确的知道关键帧的相机姿态，其他帧的相机姿态都是被插值出来的。如果要手动定义数百上千个关键帧，又是相当繁琐的一项工作，因此我们下面考虑利用 python 来自动化的执行上述过程，自动化的定义关键帧，指定相机的运动。

2.2 Python 自动化渲染

首先，总结一下前一章节手动渲染的过程，整体上可以分为如下 4 个步骤：

导入 MetaHuman 角色，并将其定位的合适位置
创建关卡序列，并创建 CineCameraActor 轨道序列
设置相机参数，并指定相机的位置和旋转，定义相机的运动方式
导出渲染的视频、图片序列

上述 4 个步骤中，除了步骤一还需要我们手动操作以外，其余步骤全部都可以利用 python 脚本来实现。在 UE4 中使用 python 接口还需要进行一些简单的配置，具体操作可以参考：https://www.bilibili.com/video/BV1PE411d7z8

步骤一：角色导入以及人脸定位

由于我只想渲染 MetaHuman 的人脸区域，因此我需要将其余身体部分移动到相机视野之外。需要移动的身体部位有：Torso、Legs、Feet。

接着进行 MetaHuman 的定位，为了方便，我们可以将其 Face 位置定位在坐标原点（0,0,0），这是为了方便后面指定相机的位置与旋转。

步骤二：指定相机运动方式：位置和旋转

在这一步，我希望相机能够以 MetaHuman 的人脸（也就是坐标原点）为中心，做球形旋转运动。关于相机的外参，做如下设置：

相机到坐标原点的距离（即：球半径）为35
相机的俯仰角设置为如下角度：[-30， -15， 0， 15， 30]
在每个俯仰角下，偏航角区间设置为：[-180, 180]，每间隔角度 10 定义一个关键点（即：拍摄一张照片）

渲染的相关的设置如下：

相机的视场角设置为：100
所渲染图片的分辨率：512
帧与帧之间的延迟：1.5

相机内参的设置见：步骤三具体的渲染代码。

现在，我们将相机的运动数据（相机位置和旋转）、渲染的相关设置，存为一个 .json 文件，在步骤三渲染的时候直接读取这些数据即可。代码如下：


import json
import numpy as np
 
# 得到相机的运动数据（位置、旋转）
def get_camera_transform():
    radius = 35
    camara_transform = []
 
    for y_pitch in range(-30, 31, 15):
        for z_yaw in range(-180, 181, 10):
            location_x = radius * np.cos(z_yaw / 180 * np.pi) * np.cos(y_pitch / 180 * np.pi)
            location_y = radius * np.sin(z_yaw / 180 * np.pi) * np.cos(y_pitch / 180 * np.pi)
            location_z = -radius * np.sin(y_pitch / 180 * np.pi)
 
            print([-location_x, -location_y, location_z, 0, y_pitch, z_yaw])
            camara_transform.append([-location_x, -location_y, location_z, 0, y_pitch, z_yaw])
 
    return camara_transform
 
# 将基础数据存为一个 .json 文件
def make_json():
    camara_transform = get_camera_transform()
 
    data_dict = {
        f"film_fov": 100,
        "film_resolution": 512,
        "delay_every_frame": 1.5,
        "output_image_path": "F:/projects/Unreal projects/MetaHumanRender/RenderImages/Danielle/face_hair",
        "camera_data": {
            "camera_qRrq9DqY": {
                "type": "Camera",
                "camera_transform": camara_transform
            }
        }
    }
 
    data_json = json.dumps(data_dict, indent=4)
    with open("camera_data.json", 'w') as json_file:
        json_file.write(data_json)
 
 
if __name__ == '__main__':
    make_json()

步骤三：读取相机运动数据，创建关卡序列添加关键帧

首先，读取上一节生成的.json文件，获取相机运动数据


def read_json_file(path):
    file = open(path, "rb")
    file_json = json.load(file)
 
    export_path = file_json['output_image_path']  # image export path
    film_fov = file_json.get('film_fov', None)  # camera film fov
    film_resolution = file_json.get("film_resolution", 512)  # camera file resolution
    delay_every_frame = file_json.get("delay_every_frame", 3.0)  # sequence run delay every frame
    camera_json = file_json['camera_data']  # camera data
 
    camera_transform_array = []
    camera_rotation_array = []
    camera_name_array = []
    for camera in camera_json:
        camera_transform = camera_json[camera]["camera_transform"]
        for index in range(len(camera_transform)):
 
            camera_transform_array.append(unreal.Transform(
                location=[camera_transform[index][0], camera_transform[index][1], camera_transform[index][2]],
                rotation=[camera_transform[index][3], camera_transform[index][4], camera_transform[index][5]],
                scale=[1.0, 1.0, 1.0]
            ))
            camera_rotation_array.append(unreal.Rotator(
                roll=camera_transform[index][3],
                pitch=camera_transform[index][4],
                yaw=camera_transform[index][5]
            ))
        camera_name_array.append(camera)
 
    return camera_transform_array, camera_rotation_array, camera_name_array, export_path, film_fov, film_resolution, delay_every_frame

接着创建关卡序列，并添加关键帧，每一个相机姿态对应一个关键帧。在这一部分，做要做了如下几个事情，具体细节可参考代码

在场景中创建一个电影摄像机 CineCameraActor，并指定其位置和旋转。
设置胶片或数字传感器的尺寸。
相机的镜头的参数设置：最小焦距、最大焦距等。
聚焦设置：焦距、光圈、视场角等。
相机的绑定，相机的关键帧添加，对每一个相机姿态添加一个关键帧。

代码


def create_sequence(asset_name, camera_transform_array, camera_rotation_array, camera_name_array, film_fov,
                    package_path='/Game/'):
    # create a sequence
    sequence = unreal.AssetToolsHelpers.get_asset_tools().create_asset(asset_name, package_path, unreal.LevelSequence,
                                                                       unreal.LevelSequenceFactoryNew())
    sequence.set_display_rate(unreal.FrameRate(numerator=1, denominator=1))
    sequence.set_playback_start_seconds(0)
    sequence.set_playback_end_seconds(len(camera_transform_array))
 
    # add a camera cut track
    camera_cut_track = sequence.add_master_track(unreal.MovieSceneCameraCutTrack)
    print(camera_transform_array[0], '=======================================================================')
    print(camera_rotation_array[0].get_editor_property("roll"))
 
    # 添加关键帧
    for index in range(0, len(camera_name_array)):
        camera_cut_section = camera_cut_track.add_section()
        camera_cut_section.set_start_frame_bounded(6 * index)
        camera_cut_section.set_end_frame_bounded(6 * index + len(camera_transform_array))
        camera_cut_section.set_start_frame_seconds(6 * index)
        camera_cut_section.set_end_frame_seconds(6 * index + len(camera_transform_array))
 
        # Create a cine camera actor
        # 在世界编辑器中创建一个电影摄像机CineCameraActor,并指定位置和旋转
        camera_actor = unreal.EditorLevelLibrary().spawn_actor_from_class(unreal.CineCameraActor,
                                                                          unreal.Vector(0, 0, 0),
                                                                          unreal.Rotator(0, 0, 0))
        # 指定电影摄像机CineCameraActor的名称
        camera_actor.set_actor_label(camera_name_array[index])
        # 返回CineCamera组件
        camera_component = camera_actor.get_cine_camera_component()
        ratio = math.tan(film_fov / 360.0 * math.pi) * 2
 
        # step1：胶片背板设置
        filmback = camera_component.get_editor_property("filmback")
        # sensor_height：胶片或数字传感器的垂直尺寸，以毫米为单位
        filmback.set_editor_property("sensor_height", 60)
        # sensor_width：胶片或数字传感器的水平尺寸，以毫米为单位
        filmback.set_editor_property("sensor_width", 60)
 
        # step2：镜头设置
        lens_settings = camera_component.get_editor_property("lens_settings")
        lens_settings.set_editor_property("min_focal_length", 4.0)
        lens_settings.set_editor_property("max_focal_length", 1000)
        lens_settings.set_editor_property("min_f_stop", 1.2)
        lens_settings.set_editor_property("max_f_stop", 500)
        print(lens_settings)
 
        # step3：聚焦设置
        focal_length = 45  # 焦距
        current_aperture = 500  # 光圈
        camera_component.set_editor_property("current_focal_length", focal_length)  # 设置当前焦距
        camera_component.set_editor_property("current_aperture", current_aperture)  # 设置当前光圈
        fov = camera_component.get_editor_property("field_of_view")
        print(camera_component.get_editor_property("current_focal_length"))
        print(camera_component.get_editor_property("current_aperture"))
        print(f"fov - {fov}")
 
        # add a binding for the camera
        camera_binding = sequence.add_possessable(camera_actor)
        transform_track = camera_binding.add_track(unreal.MovieScene3DTransformTrack)
        transform_section = transform_track.add_section()
        transform_section.set_start_frame_bounded(6 * index)
        transform_section.set_end_frame_bounded(6 * index + len(camera_transform_array))
        transform_section.set_start_frame_seconds(6 * index)
        transform_section.set_end_frame_seconds(6 * index + len(camera_transform_array))
 
        # get channel for location_x location_y location_z
        channel_location_x = transform_section.get_channels()[0]
        channel_location_y = transform_section.get_channels()[1]
        channel_location_z = transform_section.get_channels()[2]
 
        # get key for rotation_y rotation_z
        channel_rotation_x = transform_section.get_channels()[3]
        channel_rotation_y = transform_section.get_channels()[4]
        channel_rotation_z = transform_section.get_channels()[5]
 
        # camera_transform = camera_transform_array[index]
        # camera_location_x = camera_transform.get_editor_property("translation").get_editor_property("x")
        # camera_location_y = camera_transform.get_editor_property("translation").get_editor_property("y")
        # camera_location_z = camera_transform.get_editor_property("translation").get_editor_property("z")
 
        for i in range(len(camera_transform_array)):
            camera_transform = camera_transform_array[i]
            camera_location_x = camera_transform.get_editor_property("translation").get_editor_property("x")
            camera_location_y = camera_transform.get_editor_property("translation").get_editor_property("y")
            camera_location_z = camera_transform.get_editor_property("translation").get_editor_property("z")
            camera_rotation = camera_rotation_array[i]
            camera_rotate_roll = camera_rotation.get_editor_property("roll")
            camera_rotate_pitch = camera_rotation.get_editor_property("pitch")
            camera_rotate_yaw = camera_rotation.get_editor_property("yaw")
 
            new_time = unreal.FrameNumber(value=i)
            channel_location_x.add_key(new_time, camera_location_x, 0.0)
            channel_location_y.add_key(new_time, camera_location_y, 0.0)
            channel_location_z.add_key(new_time, camera_location_z, 0.0)
            channel_rotation_x.add_key(new_time, camera_rotate_roll, 0.0)
            channel_rotation_y.add_key(new_time, camera_rotate_pitch, 0.0)
            channel_rotation_z.add_key(new_time, camera_rotate_yaw, 0.0)
 
            # if i % 5 == 0:
            #     print(new_time, [camera_location_x, camera_location_y, camera_location_z, camera_rotate_roll, camera_rotate_pitch, camera_rotate_yaw])
 
 
        # add the binding for the camera cut section
        camera_binding_id = sequence.make_binding_id(camera_binding, unreal.MovieSceneObjectBindingSpace.LOCAL)
        camera_cut_section.set_camera_binding_id(camera_binding_id)
 
    # save sequence asset
    unreal.EditorAssetLibrary.save_loaded_asset(sequence, False)
 
    return sequence

步骤四：将关卡序列渲染为视频、图片序列

将创建的关卡序列渲染为电影序列，这部分主要就是设置一些渲染参数，对应手动渲染的 step5，具体参数的含义可参考 unreal 官方文档。代码如下：


# sequence movie
def render_sequence_to_movie(export_path, film_resolution, delay_every_frame, on_finished_callback):
    # 1) Create an instance of our UAutomatedLevelSequenceCapture and override all of the settings on it. This class is currently
    # set as a config class so settings will leak between the Unreal Sequencer Render-to-Movie UI and this object. To work around
    # this, we set every setting via the script so that no changes the user has made via the UI will affect the script version.
    # The users UI settings will be reset as an unfortunate side effect of this.
    capture_settings = unreal.AutomatedLevelSequenceCapture()
 
    # Set all POD settings on the UMovieSceneCapture
    # capture_settings.settings.output_directory = unreal.DirectoryPath("../../../unreal-render-release/Saved/VideoCaptures1/")
    capture_settings.settings.output_directory = unreal.DirectoryPath(export_path)
 
    # If you game mode is implemented in Blueprint, load_asset(...) is going to return you the C++ type ('Blueprint') and not what the BP says it inherits from.
    # Instead, because game_mode_override is a TSubclassOf<AGameModeBase> we can use unreal.load_class to get the UClass which is implicitly convertable.
    # ie: capture_settings.settings.game_mode_override = unreal.load_class(None, "/Game/AI/TestingSupport/AITestingGameMode.AITestingGameMode_C")
    capture_settings.settings.game_mode_override = None
    capture_settings.settings.output_format = "{camera}" + "_{frame}"
    capture_settings.settings.overwrite_existing = False
    capture_settings.settings.use_relative_frame_numbers = False
    capture_settings.settings.handle_frames = 0
    capture_settings.settings.zero_pad_frame_numbers = 4
    # If you wish to override the output framerate you can use these two lines, otherwise the framerate will be derived from the sequence being rendered
    capture_settings.settings.use_custom_frame_rate = False
    # capture_settings.settings.custom_frame_rate = unreal.FrameRate(24,1)
    capture_settings.settings.resolution.res_x = film_resolution
    capture_settings.settings.resolution.res_y = film_resolution
    capture_settings.settings.enable_texture_streaming = False
    capture_settings.settings.cinematic_engine_scalability = True
    capture_settings.settings.cinematic_mode = True
    capture_settings.settings.allow_movement = False  # Requires cinematic_mode = True
    capture_settings.settings.allow_turning = False  # Requires cinematic_mode = True
    capture_settings.settings.show_player = False  # Requires cinematic_mode = True
    capture_settings.settings.show_hud = False  # Requires cinematic_mode = True
    capture_settings.use_separate_process = False
    capture_settings.close_editor_when_capture_starts = False  # Requires use_separate_process = True
    capture_settings.additional_command_line_arguments = "-NOSCREENMESSAGES"  # Requires use_separate_process = True
    capture_settings.inherited_command_line_arguments = ""  # Requires use_separate_process = True
 
    # Set all the POD settings on UAutomatedLevelSequenceCapture
    capture_settings.use_custom_start_frame = False  # If False, the system will automatically calculate the start based on sequence content
    capture_settings.use_custom_end_frame = False  # If False, the system will automatically calculate the end based on sequence content
    capture_settings.custom_start_frame = unreal.FrameNumber(0)  # Requires use_custom_start_frame = True
    capture_settings.custom_end_frame = unreal.FrameNumber(0)  # Requires use_custom_end_frame = True
    capture_settings.warm_up_frame_count = 0
    capture_settings.delay_before_warm_up = 0
    capture_settings.delay_before_shot_warm_up = 0
    capture_settings.delay_every_frame = delay_every_frame
    capture_settings.write_edit_decision_list = True
 
    # Tell the capture settings which level sequence to render with these settings. The asset does not need to be loaded,
    # as we're only capturing the path to it and when the PIE instance is created it will load the specified asset.
    # If you only had a reference to the level sequence, you could use "unreal.SoftObjectPath(mysequence.get_path_name())"
    capture_settings.level_sequence_asset = unreal.SoftObjectPath(sequence_asset_path)
    # To configure the video output we need to tell the capture settings which capture protocol to use. The various supported
    # capture protocols can be found by setting the Unreal Content Browser to "Engine C++ Classes" and filtering for "Protocol"
    # ie: CompositionGraphCaptureProtocol, ImageSequenceProtocol_PNG, etc. Do note that some of the listed protocols are not intended
    # to be used directly.
    # Right click on a Protocol and use "Copy Reference" and then remove the extra formatting around it. ie:
    # Class'/Script/MovieSceneCapture.ImageSequenceProtocol_PNG' gets transformed into "/Script/MovieSceneCapture.ImageSequenceProtocol_PNG"
    capture_settings.set_image_capture_protocol_type(
        unreal.load_class(None, "/Script/MovieSceneCapture.ImageSequenceProtocol_PNG"))
    # After we have set the capture protocol to a soft class path we can start editing the settings for the instance of the protocol that is internallyc reated.
    capture_settings.get_image_capture_protocol().compression_quality = 85
    # Finally invoke Sequencer's Render to Movie functionality. This will examine the specified settings object and either construct a new PIE instance to render in,
    # or create and launch a new process (optionally shutting down your editor).
    unreal.SequencerTools.render_movie(capture_settings, on_finished_callback)

2.3 全部代码


import sys
 
import unreal, os, json, math
 
# sequence asset path
sequence_asset_path = '/Game/Render_Sequence.Render_Sequence'
 
 
# read json file
def read_json_file(path):
    file = open(path, "rb")
    file_json = json.load(file)
 
    export_path = file_json['output_image_path']  # image export path
    film_fov = file_json.get('film_fov', None)  # camera film fov
    film_resolution = file_json.get("film_resolution", 512)  # camera file resolution
    delay_every_frame = file_json.get("delay_every_frame", 3.0)  # sequence run delay every frame
    camera_json = file_json['camera_data']  # camera data
 
    camera_transform_array = []
    camera_rotation_array = []
    camera_name_array = []
    for camera in camera_json:
        camera_transform = camera_json[camera]["camera_transform"]
        for index in range(len(camera_transform)):
 
            camera_transform_array.append(unreal.Transform(
                location=[camera_transform[index][0], camera_transform[index][1], camera_transform[index][2]],
                rotation=[camera_transform[index][3], camera_transform[index][4], camera_transform[index][5]],
                scale=[1.0, 1.0, 1.0]
            ))
            camera_rotation_array.append(unreal.Rotator(
                roll=camera_transform[index][3],
                pitch=camera_transform[index][4],
                yaw=camera_transform[index][5]
            ))
        camera_name_array.append(camera)
 
    return camera_transform_array, camera_rotation_array, camera_name_array, export_path, film_fov, film_resolution, delay_every_frame
 
 
def create_sequence(asset_name, camera_transform_array, camera_rotation_array, camera_name_array, film_fov,
                    package_path='/Game/'):
    # create a sequence
    sequence = unreal.AssetToolsHelpers.get_asset_tools().create_asset(asset_name, package_path, unreal.LevelSequence,
                                                                       unreal.LevelSequenceFactoryNew())
    sequence.set_display_rate(unreal.FrameRate(numerator=1, denominator=1))
    sequence.set_playback_start_seconds(0)
    sequence.set_playback_end_seconds(len(camera_transform_array))
 
    # add a camera cut track
    camera_cut_track = sequence.add_master_track(unreal.MovieSceneCameraCutTrack)
    print(camera_transform_array[0], '=======================================================================')
    print(camera_rotation_array[0].get_editor_property("roll"))
 
    # 添加关键帧
    for index in range(0, len(camera_name_array)):
        camera_cut_section = camera_cut_track.add_section()
        camera_cut_section.set_start_frame_bounded(6 * index)
        camera_cut_section.set_end_frame_bounded(6 * index + len(camera_transform_array))
        camera_cut_section.set_start_frame_seconds(6 * index)
        camera_cut_section.set_end_frame_seconds(6 * index + len(camera_transform_array))
 
        # Create a cine camera actor
        # 在世界编辑器中创建一个电影摄像机CineCameraActor,并指定位置和旋转
        camera_actor = unreal.EditorLevelLibrary().spawn_actor_from_class(unreal.CineCameraActor,
                                                                          unreal.Vector(0, 0, 0),
                                                                          unreal.Rotator(0, 0, 0))
        # 指定电影摄像机CineCameraActor的名称
        camera_actor.set_actor_label(camera_name_array[index])
        # 返回CineCamera组件
        camera_component = camera_actor.get_cine_camera_component()
        ratio = math.tan(film_fov / 360.0 * math.pi) * 2
 
        # step1：胶片背板设置
        filmback = camera_component.get_editor_property("filmback")
        # sensor_height：胶片或数字传感器的垂直尺寸，以毫米为单位
        filmback.set_editor_property("sensor_height", 60)
        # sensor_width：胶片或数字传感器的水平尺寸，以毫米为单位
        filmback.set_editor_property("sensor_width", 60)
 
        # step2：镜头设置
        lens_settings = camera_component.get_editor_property("lens_settings")
        lens_settings.set_editor_property("min_focal_length", 4.0)
        lens_settings.set_editor_property("max_focal_length", 1000)
        lens_settings.set_editor_property("min_f_stop", 1.2)
        lens_settings.set_editor_property("max_f_stop", 500)
        print(lens_settings)
 
        # step3：聚焦设置
        focal_length = 45  # 焦距
        current_aperture = 500  # 光圈
        camera_component.set_editor_property("current_focal_length", focal_length)  # 设置当前焦距
        camera_component.set_editor_property("current_aperture", current_aperture)  # 设置当前光圈
        fov = camera_component.get_editor_property("field_of_view")
        print(camera_component.get_editor_property("current_focal_length"))
        print(camera_component.get_editor_property("current_aperture"))
        print(f"fov - {fov}")
 
        # add a binding for the camera
        camera_binding = sequence.add_possessable(camera_actor)
        transform_track = camera_binding.add_track(unreal.MovieScene3DTransformTrack)
        transform_section = transform_track.add_section()
        transform_section.set_start_frame_bounded(6 * index)
        transform_section.set_end_frame_bounded(6 * index + len(camera_transform_array))
        transform_section.set_start_frame_seconds(6 * index)
        transform_section.set_end_frame_seconds(6 * index + len(camera_transform_array))
 
        # get channel for location_x location_y location_z
        channel_location_x = transform_section.get_channels()[0]
        channel_location_y = transform_section.get_channels()[1]
        channel_location_z = transform_section.get_channels()[2]
 
        # get key for rotation_y rotation_z
        channel_rotation_x = transform_section.get_channels()[3]
        channel_rotation_y = transform_section.get_channels()[4]
        channel_rotation_z = transform_section.get_channels()[5]
 
        # camera_transform = camera_transform_array[index]
        # camera_location_x = camera_transform.get_editor_property("translation").get_editor_property("x")
        # camera_location_y = camera_transform.get_editor_property("translation").get_editor_property("y")
        # camera_location_z = camera_transform.get_editor_property("translation").get_editor_property("z")
 
        for i in range(len(camera_transform_array)):
            camera_transform = camera_transform_array[i]
            camera_location_x = camera_transform.get_editor_property("translation").get_editor_property("x")
            camera_location_y = camera_transform.get_editor_property("translation").get_editor_property("y")
            camera_location_z = camera_transform.get_editor_property("translation").get_editor_property("z")
            camera_rotation = camera_rotation_array[i]
            camera_rotate_roll = camera_rotation.get_editor_property("roll")
            camera_rotate_pitch = camera_rotation.get_editor_property("pitch")
            camera_rotate_yaw = camera_rotation.get_editor_property("yaw")
 
            new_time = unreal.FrameNumber(value=i)
            channel_location_x.add_key(new_time, camera_location_x, 0.0)
            channel_location_y.add_key(new_time, camera_location_y, 0.0)
            channel_location_z.add_key(new_time, camera_location_z, 0.0)
            channel_rotation_x.add_key(new_time, camera_rotate_roll, 0.0)
            channel_rotation_y.add_key(new_time, camera_rotate_pitch, 0.0)
            channel_rotation_z.add_key(new_time, camera_rotate_yaw, 0.0)
 
            # if i % 5 == 0:
            #     print(new_time, [camera_location_x, camera_location_y, camera_location_z, camera_rotate_roll, camera_rotate_pitch, camera_rotate_yaw])
 
 
        # add the binding for the camera cut section
        camera_binding_id = sequence.make_binding_id(camera_binding, unreal.MovieSceneObjectBindingSpace.LOCAL)
        camera_cut_section.set_camera_binding_id(camera_binding_id)
 
    # save sequence asset
    unreal.EditorAssetLibrary.save_loaded_asset(sequence, False)
 
    return sequence
 
 
# sequence movie
def render_sequence_to_movie(export_path, film_resolution, delay_every_frame, on_finished_callback):
    # 1) Create an instance of our UAutomatedLevelSequenceCapture and override all of the settings on it. This class is currently
    # set as a config class so settings will leak between the Unreal Sequencer Render-to-Movie UI and this object. To work around
    # this, we set every setting via the script so that no changes the user has made via the UI will affect the script version.
    # The users UI settings will be reset as an unfortunate side effect of this.
    capture_settings = unreal.AutomatedLevelSequenceCapture()
 
    # Set all POD settings on the UMovieSceneCapture
    # capture_settings.settings.output_directory = unreal.DirectoryPath("../../../unreal-render-release/Saved/VideoCaptures1/")
    capture_settings.settings.output_directory = unreal.DirectoryPath(export_path)
 
    # If you game mode is implemented in Blueprint, load_asset(...) is going to return you the C++ type ('Blueprint') and not what the BP says it inherits from.
    # Instead, because game_mode_override is a TSubclassOf<AGameModeBase> we can use unreal.load_class to get the UClass which is implicitly convertable.
    # ie: capture_settings.settings.game_mode_override = unreal.load_class(None, "/Game/AI/TestingSupport/AITestingGameMode.AITestingGameMode_C")
    capture_settings.settings.game_mode_override = None
    capture_settings.settings.output_format = "{camera}" + "_{frame}"
    capture_settings.settings.overwrite_existing = False
    capture_settings.settings.use_relative_frame_numbers = False
    capture_settings.settings.handle_frames = 0
    capture_settings.settings.zero_pad_frame_numbers = 4
    # If you wish to override the output framerate you can use these two lines, otherwise the framerate will be derived from the sequence being rendered
    capture_settings.settings.use_custom_frame_rate = False
    # capture_settings.settings.custom_frame_rate = unreal.FrameRate(24,1)
    capture_settings.settings.resolution.res_x = film_resolution
    capture_settings.settings.resolution.res_y = film_resolution
    capture_settings.settings.enable_texture_streaming = False
    capture_settings.settings.cinematic_engine_scalability = True
    capture_settings.settings.cinematic_mode = True
    capture_settings.settings.allow_movement = False  # Requires cinematic_mode = True
    capture_settings.settings.allow_turning = False  # Requires cinematic_mode = True
    capture_settings.settings.show_player = False  # Requires cinematic_mode = True
    capture_settings.settings.show_hud = False  # Requires cinematic_mode = True
    capture_settings.use_separate_process = False
    capture_settings.close_editor_when_capture_starts = False  # Requires use_separate_process = True
    capture_settings.additional_command_line_arguments = "-NOSCREENMESSAGES"  # Requires use_separate_process = True
    capture_settings.inherited_command_line_arguments = ""  # Requires use_separate_process = True
 
    # Set all the POD settings on UAutomatedLevelSequenceCapture
    capture_settings.use_custom_start_frame = False  # If False, the system will automatically calculate the start based on sequence content
    capture_settings.use_custom_end_frame = False  # If False, the system will automatically calculate the end based on sequence content
    capture_settings.custom_start_frame = unreal.FrameNumber(0)  # Requires use_custom_start_frame = True
    capture_settings.custom_end_frame = unreal.FrameNumber(0)  # Requires use_custom_end_frame = True
    capture_settings.warm_up_frame_count = 0
    capture_settings.delay_before_warm_up = 0
    capture_settings.delay_before_shot_warm_up = 0
    capture_settings.delay_every_frame = delay_every_frame
    capture_settings.write_edit_decision_list = True
 
    # Tell the capture settings which level sequence to render with these settings. The asset does not need to be loaded,
    # as we're only capturing the path to it and when the PIE instance is created it will load the specified asset.
    # If you only had a reference to the level sequence, you could use "unreal.SoftObjectPath(mysequence.get_path_name())"
    capture_settings.level_sequence_asset = unreal.SoftObjectPath(sequence_asset_path)
    # To configure the video output we need to tell the capture settings which capture protocol to use. The various supported
    # capture protocols can be found by setting the Unreal Content Browser to "Engine C++ Classes" and filtering for "Protocol"
    # ie: CompositionGraphCaptureProtocol, ImageSequenceProtocol_PNG, etc. Do note that some of the listed protocols are not intended
    # to be used directly.
    # Right click on a Protocol and use "Copy Reference" and then remove the extra formatting around it. ie:
    # Class'/Script/MovieSceneCapture.ImageSequenceProtocol_PNG' gets transformed into "/Script/MovieSceneCapture.ImageSequenceProtocol_PNG"
    capture_settings.set_image_capture_protocol_type(
        unreal.load_class(None, "/Script/MovieSceneCapture.ImageSequenceProtocol_PNG"))
    # After we have set the capture protocol to a soft class path we can start editing the settings for the instance of the protocol that is internallyc reated.
    capture_settings.get_image_capture_protocol().compression_quality = 85
    # Finally invoke Sequencer's Render to Movie functionality. This will examine the specified settings object and either construct a new PIE instance to render in,
    # or create and launch a new process (optionally shutting down your editor).
    unreal.SequencerTools.render_movie(capture_settings, on_finished_callback)
 
 
# sequence end call back
def on_render_movie_finished(success):
    unreal.log('on_render_movie_finished is called')
    if success:
        unreal.log('---end LevelSequenceTask')
 
 
# check asset is exist
def check_sequence_asset_exist(root_dir):
    sequence_path = os.path.join(root_dir, 'Content', 'Render_Sequence.uasset')
    if (os.path.exists(sequence_path)):
        unreal.log('---sequence is exist os path---')
        os.remove(sequence_path)
    else:
        unreal.log('---sequence is not exist os path---')
 
    if unreal.EditorAssetLibrary.does_asset_exist(sequence_asset_path):
        unreal.log('---sequence dose asset exist---')
        unreal.EditorAssetLibrary.delete_asset(sequence_asset_path)
    else:
        unreal.log('---sequence does not asset exist---')
 
    sequence_asset_data = unreal.AssetRegistryHelpers.get_asset_registry().get_asset_by_object_path(sequence_asset_path)
    if sequence_asset_data:
        unreal.log('---sequence is exist on content---')
        sequence_asset = unreal.AssetData.get_asset(sequence_asset_data)
        unreal.EditorAssetLibrary.delete_loaded_asset(sequence_asset)
    else:
        unreal.log('---sequence is not exit on content---')
 
 
def main():
    # bind event
    on_finished_callback = unreal.OnRenderMovieStopped()
    on_finished_callback.bind_callable(on_render_movie_finished)
 
    # get json file
    root_dir = unreal.SystemLibrary.get_project_directory()
    json_path = os.path.join(root_dir, 'RawData', 'camera_data.json')
 
    # get json data
    camera_transform_array, camera_rotation_array, camera_name_array, export_path, film_fov, film_resolution, delay_every_frame = read_json_file(
        json_path)
 
    # check sequence is asset
    check_sequence_asset_exist(root_dir)
 
    # create sequence
    create_sequence('Render_Sequence', camera_transform_array, camera_rotation_array, camera_name_array, film_fov)
 
    # run sequence
    render_sequence_to_movie(export_path, film_resolution, delay_every_frame, on_finished_callback)

3. 渲染结果

上图即为渲染的多视点图片，每张图片对应的相机姿态也是确定的。

至此，在 UE4 中利用 python 实现自动化渲染的整个过程就结束了。在这里留下一个小问题：

UE4 中的相机姿态数据我们是无法直接使用的，如何将其转化为 NeRF 中的相机姿态数据呢？大家可以自行探索一下，后续文章再对这一部分的内容进行讲解。

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