Bentley ContextCapture Center 官方智能三维使用教程

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"Smart3D（ContextCapture Center）是一款由Bentley Systems, Incorporated开发的专业三维建模软件，主要用于倾斜摄影测量数据的处理和三维重建。本官方使用教程提供了详尽的操作指南，覆盖了从项目创建到空三计算，再到三维模型重建的全过程。" 在该教程中，用户将学习如何利用Smart3D（也被称为ContextCapture Center）进行以下关键步骤： 1. **项目创建**：首先，用户需要了解如何设置新项目，这包括导入倾斜摄影的数据，如多视角影像照片，以及配置项目参数，如输出分辨率、坐标系统等。 2. **空三计算（Bundle Adjustment）**：空三计算是将多个二维图像对应到同一三维空间的关键步骤。教程会指导用户如何进行自动匹配点、控制点添加和优化，以确保影像的精确对齐和三维重建的精度。 3. **三维重建（Mesh Generation）**：在空三计算完成后，软件将生成三维点云，并进一步构建三角网格模型（Mesh）。这一过程涉及到点云过滤、纹理映射等技术，以生成逼真的三维场景模型。 4. **纹理映射**：利用空三计算得到的影像信息，软件可以将真实色彩贴合到模型表面，使得最终的三维模型具有高保真的视觉效果。 5. **数据管理与导出**：用户将学习如何在软件中查看、编辑和管理模型，以及如何导出不同格式的成果，如OBJ、3DS、LAS等，以供其他应用程序或平台使用。 6. **高级功能**：教程可能还会涵盖一些高级特性，如建筑物立面提取、地表分析、体积计算、GIS集成等，这些对于城市规划、地理信息系统（GIS）、测绘等领域尤其重要。 7. **许可与版权**：软件的使用受到特定的软件许可证协议约束，用户应了解并遵守版权和保密条款，特别是对于美国政府机构用户，软件使用有特定的限制权利规定。通过这个详细的官方教程，用户不仅能掌握Smart3D的基本操作，还能深入理解倾斜摄影测量的原理和技术，从而高效地利用该工具进行三维建模和分析。

Preparing the Imagery Dataset

Photo acquisition

Overlap

Each part of the subject should be photographed from at least three distinct - but not radically different -

viewpoints. The overlap between consecutive photographs should typically exceed two thirds. Different

viewpoints of the same part of the subject should be less than 15 degrees apart.

For simple subjects, you can achieve this by taking approximately 30-50 evenly spaced photographs all around

the subject.

For aerial photography, a longitudinal overlap of 80% and lateral overlap of 50% or more are recommended. To

achieve best results, acquire both vertical and oblique photographs, in order to simultaneously recover building

facades, narrow streets and courtyards. ContextCapture is remarkably robust for unstructured acquisition. You

may however prepare a flight plan for more systematic acquisitions.

Camera models

ContextCapture supports a wide range of cameras: mobile phone, compact digital, DSLR, fisheye,

photogrammetric, and multi-camera systems. It can process still photographs or extracted video frames from

digital video cameras. It does not support linear pushbroom cameras. It does not support rolling shutter cameras

under fast motion.

Although ContextCapture does not require a minimum camera resolution, a higher resolution camera allows

acquisition of a subject at a given precision with fewer photographs, and thus more quickly, than a lower

resolution camera.

ContextCapture needs to know the width of your camera's sensor. If your camera model is not already listed in

our database, you will be asked to enter this information. If you are unsure of your camera's specifications, you

can consult your camera owner's manual or the Digital Photography Review website: http://

www.dpreview.com/products.

Projected Pixel Size

In the sequel, the projected pixel size means the extension of the classical ground resolution to a more general,

possibly not aerial, acquisition configuration.

ContextCapture 16 User Guide

The resolution and precision of the generated 3D model is directly related to the projected pixel size on the

subject. In order to achieve a desired projected pixel size, you must adopt a proper combination of focal length

and distance to the subject, as defined by the formula below:

projected pixel size × focal length × photo's largest dimension = sensor width × distance to the subject

[m / pixel] [mm] [pixel] [mm] [m]

Uniform projected pixel size across the entire image is not required since ContextCapture will automatically

propagate variations in projected pixel size to the resolution and precision of the generated 3D model.

ContextCapture is unable, however, to join together photographs of radically different projected pixel sizes. If a

wide range is required, photographs with intermediate values should be used to create a smooth transition.

Focal Length

Using a fixed focal length throughout the acquisition process is recommended.

To achieve a non-uniform projected pixel size, vary the distance to the subject. If you cannot avoid several focal

length settings, e.g., if the distance to the subject is constrained, shoot several series of photographs, each with a

fixed focal length.

When using a zoom lens, make sure its position remains fixed over a series of photographs. You can use a piece

of adhesive tape with a manual zoom lens to keep it in place.

Wide-angle or fish-eye lens can be used if the suited camera model type is specified, ContextCapture can

automatically estimate extreme lens distortion.

Do not use digital zoom.

Exposure

Select exposure settings that will avoid the motion blur, defocus, noise, and over or under-exposure that can

seriously alter 3D reconstruction.

Manual exposure reduces the likelihood of color discrepancies in the texture map of the generated 3D model,

and is therefore recommended for those with the necessary photography skills and under fairly stable and

uniform lighting conditions. Otherwise, automatic exposure may be used.

Turning off optical or digital image stabilization is recommended.

Lighting

Ambient, constant lighting is preferable to direct and/or time-varying lighting, since the latter increases the risk

of overexposure and underexposure. For indoor acquisition, fixed lights are preferable to flash, and for outdoor

acquisition, clouds (high-altitude cirrus clouds, no rain) are preferable to sun. If photos must be taken on a

sunny day, take them around noon to minimize shadow areas.

Please note that correctly-exposed shadows do not affect the performance of ContextCapture , but will appear in

the texture map of the generated 3D model.

Photo Retouching

Before inputting photographs into ContextCapture , do not manipulate them, by resizing, cropping, rotating,

denoising, sharpening or adjusting brightness, contrast, saturation or hue. Make sure to deactivate your

camera's auto-rotate feature.

Preparing the Imagery Dataset

Photo acquisition

ContextCapture 17 User Guide

ContextCapture does not support stitched panoramic photographs. It requires the original photographs which

were used to create the panorama.

Photogroups

For optimal precision and performance, ContextCapture must group all photos taken by the same physical

camera with identical focal length and dimensions (identical interior orientation) in one photogroup.

ContextCapture can automatically determine relevant photogroups if photos are organized in subdirectories

according to the cameras used to shoot them: photos taken by different physical cameras (even if they are the

same model) should be placed in separate subdirectories. Conversely, all photos taken by the same physical

camera should be placed in the same subdirectory.

Masks

A mask can be associated to a photo to cause specific parts of the image (e.g., moving obstacles, reflections) to be

ignored in the workflow. A valid mask is a black and white TIFF image with the same dimensions as the photo.

Pixels of the photo corresponding to black pixels of the mask will be ignored during aerotriangulation and

reconstruction.

Masks are associated to input photographs through their file name:

• Associate a mask to one photo: for a photo named "fileName.ext", the mask file must be named

"fileName_mask.tif" and placed in the same directory as the corresponding photo.

Example: for a photograph "IMG0002564.jpg", the corresponding mask should be "IMG0002564_mask.tif"

• Associate a mask to an entire directory (requires photos of same dimensions): if present in a directory, the

file "mask.tif" is used as a mask for all photos contained in this directory.

Masks can also be assigned to photos from the user interface once photos are loaded.

Input data file formats

ContextCapture natively supports photographs in JPEG and TIFF formats. It can also read some of the more

common RAW formats. ContextCapture uses Exif metadata if present.

Supported file formats:

• JPEG

• Tag Image File Format (TIFF)

• Panasonic RAW (RW2)

• Canon RAW (CRW, CR2)

• Nikon RAW (NEF)

• Sony RAW (ARW)

• Hasselblad (3FR)

• Adobe Digital Negative (DNG)

• JPEG 2000

ContextCapture can also import frames from video files in the following formats:

• Audio Video Interleave (AVI)

• MPEG-1/MPEG-2 (MPG)

Preparing the Imagery Dataset

Input data file formats

ContextCapture 18 User Guide

• MPEG-4 (MP4)

• Windows Media Video (WMV)

• Quicktime (MOV)

Point cloud file formats

ContextCapture supports two common point cloud formats able to store scan positions:

• ASTM E57 file format (.e57)

• Cyclone point cloud export format (.ptx)

Positioning data

One of ContextCapture e's breakthrough features is its ability to handle photographs that have no positioning

data. In such a case, ContextCapture generates a 3D model with arbitrary position, rotation and scale, yet with a

plausible up vector. However, ContextCapture also natively supports several types of positioning data including

GPS tags, control points and can import potentially any other positioning data through position/rotation import

or complete block import.

GPS tags, if present in Exif metadata or in an accompanying XMP file, are automatically extracted, and can be

used to georeference the generated 3D model.

Incomplete GPS tags are ignored (with latitude and longitude coordinates but without altitude).

GPS altitude reference Sea level and WGS 84 ellipsoid are supported.

Control points should be used whenever you need better-than-GPS georeferencing accuracy, or whenever you

want to eliminate long-range geometric distortion caused by numerical error accumulation across the subject's

extent. Georeferencing requires a minimum of three control points. Addressing long-range effects demands a

higher number of well-distributed control points. The 3D position of control points must be obtained via

traditional surveying methods. For each control point, you will have to manually point out a few (2 minimum, 3+

recommended) 2D measurements in photographs through the Smart3DCapture Master graphical user interface

or a third-party tool.

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