A non-Lambertian photometric stereo under perspective projection

Under the perspective projection assumption,non-Lambertian photometric stereo is a highly non-linear problem.In this study,we present an optimized framework for reconstructing the surface normal and depth with non-Lambertian reflection models under perspective projection.By decomposing the images into diffuse and specular components,we compute the surface normal and reflectance simultaneously.We also propose a variational formulation that is robust and useful for surface reconstruction.The experiments show that our method accurately reconstructs both the surface shape and reflectance of colorful objects with non-Lambertian surfaces.

DETERMINATION OF UNKNOWN CAMERA PARAMETERS FOR THE PERSPECTIVE IMAGES

To obtain an accurate 3 D object configuration from images,the essential perspective characteristics must be considered. Several new inverse transformation relations of the perspective image lines are given. Utilizing the analytic transformation relations, an optimization procedure for obtaining the unknown camera parameters of images is presented in this paper. A 3 D reproduction method and examples are introduced.

A Hidden-Removal Model of Dam Perspective Drawing

Aming at water conservancy project visualization, a hidden-removal method of dam perspective drawings is realized by building a hidden-removal mathematical model for overlapping points location to set up the hidden relationship among point and plane, plane and plane in space. On this basis, as an example of panel rockfill dam, a dam hidden-removal perspective drawing is generated in different directions and different visual angles through adapting VC＋＋ and OpenGL visualizing technology. The results show that the data construction of the model is simple which can overcome the disadvantages of considerable and complicated calculation. This method also provides the new means to draw hidden-removal perspective drawings for those landforms and ground objects.

Optimization of Enterprise Training System from The Perspective of Project Management

At present,there are a series of problems in the enterprise training system,such as the lack of systematic management,imperfect management and control measures,the lack of scienti＇c evaluation system,and so on.With the rapid development of information technology,the members of the enterprise should not only strengthen their own learning,but also promote each other.The training system of the enterprise should effectively take these needs as the preferred factors to establish and optimize the system.Based on this urgent need,this paper will put forward some thoughts on the optimization of enterprise training system from the perspective of project management.

Spacecraft Pose Estimation Based on Different Camera Models

Spacecraft pose estimation is an important technology to maintain or change the spacecraft orientation in space.For spacecraft pose estimation,when two spacecraft are relatively distant,the depth information of the space point is less than that of the measuring distance,so the camera model can be seen as a weak perspective projection model.In this paper,a spacecraft pose estimation algorithm based on four symmetrical points of the spacecraft outline is proposed.The analytical solution of the spacecraft pose is obtained by solving the weak perspective projection model,which can satisfy the requirements of the measurement model when the measurement distance is long.The optimal solution is obtained from the weak perspective projection model to the perspective projection model,which can meet the measurement requirements when the measuring distance is small.The simulation results show that the proposed algorithm can obtain better results,even though the noise is large.

Calibration method for multi-line structured light vision sensor based on Plücker line

For the rapid calibration of multi-line structured light system,a method based on Plücker line was proposed.Most of the conventional line-structured light calibration methods extract the feature points and transform the coordinates of points to obtain the plane equation.However,a large number of points lead to complicated operation which is not suitable for the application scenarios of multi-line structured light.To solve this issue,a new calibration method was proposed that applied the form of Plücker matrix throughout the whole calibration process,instead of using the point characteristics directly.The advantage of this method is that the light plane equation can be obtained quickly and accurately in the camera coordinate frame.Correspondingly a planar target particularly for calibrating multi-line structured light was also designed.The regular lines were transformed into Plücker lines by extending the two-dimensional image plane and defining a new image space.To transform the coordinate frame of Plücker lines,the perspective projection mathematical model was re-expressed based on the Plücker matrix.According to the properties of the line and plane in the Plücker space,a linear matrix equation was efficiently constructed by combining the Plücker matrices of several coplanar lines so that the line-structured light plane equation could be furtherly solved.The experiments performed validate the proposed method and demonstrate the significant improvement in the calibration accuracy,when the test distance is 1.8 m,the root mean square(RMS)error of the three-dimensional point is within 0.08 mm.

Linear perspective shape-from-shading method with two images

Shape-from-shading(SFS) is one of the important approaches of 3-D surface reconstruction in computer vision. Since reflectance map equation in SFS is a nonlinear partial differential equation(PDE) with two unknown variables, SFS with one image is ill-posed in mathematical sense. A linear perspective SFS method with two images is proposed to deal with the problem. We assume that two images with different light source directions are captured firstly. Orthogonal projection is not as accurate as perspective one to simulate imaging processes. Two reflectance map equations are established based on the Lambertian model under perspective projection, and the equations are further transformed into one linear PDE. Then the iterative semi-Lagrangian algorithm is used to approximate the solution. Finally, 3-D height values of pixel points in imaging planes are solved by the numerical interpolation method. Experimental results of both hemisphere and complex surfaces show that the proposed method can reconstruct surfaces accurately.

Everything moves:The rapid changes in photogrammetry and remote sensing

Changes in technology are coming at an ever increasing pace.This holds for photogrammetry and remote sensing as well.“Everything moves”-this is why I chose this topic to shed some light on some of the recent developments.Naturally,this undertaking can never be complete in the sense of covering all developments in Photogrammetry and Remote Sensing.Besides,the impact of Deep Learning in photogrammetry is not mentioned in this paper.This is a very personal account.People may not agree with some of my findings,but this is in the nature of science.In any case,this contribution is meant as a tribute to Gottfried’s successful lifelong work.It is not a scientific paper in the traditional sense but rather a collection of thoughts that emerged over the 50 years of my professional career.It is also meant for an audience who has not necessarily a deep photogrammetric expert know-how.

Photometric stereo for strong specular highlights

Photometric stereo is a fundamental technique in computer vision known to produce 3D shape with high accuracy. It uses several input images of a static scene taken from one and the same camera position but under varying illumination. The vast majority of studies in this 3D reconstruction method assume orthographic projection for the camera model.In addition, they mainly use the Lambertian reflectance model as the way that light scatters at surfaces.Thus, providing reliable photometric stereo results from real world objects still remains a challenging task. We address 3D reconstruction by use of a more realistic set of assumptions, combining for the first time the complete Blinn–Phong reflectance model and perspective projection. Furthermore, we compare two different methods of incorporating the perspective projection into our model. Experiments are performed on both synthetic and real world images; the latter do not benefit from laboratory conditions. The results show the high potential of our method even for complex real world applications such as medical endoscopy images which may include many specular highlights.