An Oblique-imagery Case with Pix4Dmapper

Lisa Chen

Pix4D today

• Terrestrial / Aerial mapping

• 3D modeling

• Headquarters in Lausanne (CH)

• Pix4D Inc. San Francisco (USA)

• Office Shanghai (China)

• 50 employees

• More than 140 partners worldwide

• 8000+ active users

• 50+ projects on cloud every day

Various Sensors Supported

Case Information

Location: NashvilleNumber of Images: 596Ground Sampling Distance: 8 cmImage Acquisition Time: 15 minutesProcessing Time: 6 hoursNo Ground Control Points Used

Flight Plan

Patented Flight Plan

Manned Aircraft with Xcam-B Sensor Onboard

Sample Images from the Camera Rig

Pix4Dmapper Process

Finding Keypoints on Each Image Matching the Found Keypoints Among All the Images

Densified 3D Point Cloud Generate DSM and Orthomosaic

Initial Processing

Camera Rigs

The Camera Rig Used in the Project

The Camera Positions and 3D Point Cloud displayed in Pix4Dmapper rayCloud Interface

Camera RigsRelative Position of the Camera Rig

Indicates images from Camera Rigs in Pix4Dmapper

Camera Rig Calibration Interface Which Shows the Relatives and Corresponded Accuracy

rayCloud Editor

rayCloud in 3D is corresponded to the Original Images

Matched Points shown in Orange Circle

rayCloud

Two ray intersection has large error in the direction of the rays

rayCloud

Reduce the Error by intersecting from Multiview images

Error Ellipse (Ellipsoid)

Check the Accuracy of the Manual Tie Points by Viewing the Error Ellipse in rayCloud Editor Interface

Error Ellipse (Ellipsoid)

Check the Accuracy of the Manual Tie Points by Reviewing the Statistics on the Right and the Optimized Position on the Images

Point cloud and Mesh

3D Patches and NCC ScoreGenerate (by default) 7x7 3D patches from the feature points

Each records the point location and the norms

The 3D patches will describe the surface in more details

Image Pyramid

Multiscale: Image Pyramids ComputedLarge Objects may not be well defined by 3D (default) 7x7 patchesWith Multi Image Scale, Objects can then be well described

Dense Matching

The advantage of acquiring oblique imagery:

Assist both the initial and dense matching

Get more information on the façades which better defines the surfaces, especially for building corners

3D Textured Mesh Generated

Computed Triangle meshes and the textures The smoothness of the interpolation depends on the derivatives taken (C0 C1 C2)For oblique image cases, more triangles will provide sharper edges due to more content for the façades