Detecting surface irregularities using isophotes

doi:10.1016/0167-8396(84)90028-1

Computer Aided Geometric Design

Volume 1, Issue 2, November 1984, Pages 163-168

https://doi.org/10.1016/0167-8396(84)90028-1 Get rights and content

Abstract

This contribution refers to the use of lines of equal light intensity, called isophotes, for detecting irregularities of free form surfaces in car body construction. The isophotes show irregularities of surface smoothness, of the Gaussian curvature and of the distribution of the surface normals. The algorithm described wasrealized in the CADCAM-system Ogsurf-P a, Volkswagen development for car body design and manufacturing.

References (7)

H. Henning
Fuenfachsiges NC-Fraesen gekruemmter Flaechen
(1972)
E. Kamke
Differentialgleichungen, Loesungsmethoden und Loesungen
(1956)
B. Klass
Correction of local surface irregularities using reflection lines

There are more references available in the full text version of this article.

Cited by (77)

Contour curves and isophotes on rational ruled surfaces
2018, Computer Aided Geometric Design
Ruled surfaces, i.e., surfaces generated by a one-parametric set of lines, are widely used in the field of applied geometry. An isophote on a surface is a curve consisting of those surface points whose normals form a constant angle with a fixed vector. Choosing the angle equal to $π / 2$ we obtain a special instance of the isophote – the so called contour curve. While contours on rational ruled surfaces are rational curves, this is no longer true for the isophotes. Hence we will provide a formula for their genus. Moreover we will show that the only surfaces with a rational generic contour are just the rational ruled surfaces and a particular class of cubic surfaces. In addition we will deal with a reconstruction of ruled surfaces from their silhouettes.
Using isophotes and shadows to interactively model normal and height fields
2016, Computers and Graphics (Pergamon)
Citation Excerpt :
3D sketch modeling research has also noted the use of shading as a handle for editing a 3D shape by editing its smooth shading [26]; their approach requires a pre-existing 3D shape and is not designed to create one purely from shading. Isophotes and reflection lines: Fair surface design often employs isophotes and reflection lines [27] to directly visualize the continuity of the surface gradient [28]. Deslandes and Bonner [29] describe an approach for exactly specifying reflection lines by modifying an existing 3D shape.
We introduce an interactive modeling tool for designing (a) a smooth 3D normal field from the isophotes of a discretely shaded 2D image and (b) lifting the normal field into a smooth height field given a cast shadow. Block or cartoon shading is a visual style in which artists depict a smoothly shaded 3D object using a small number of discrete brightness values, manifested as regions or bands of constant color. In our approach, artists trace isophotes, or curves of constant brightness, along the boundaries between constant color bands. Our algorithm first estimates light directions and computes 3D normals along the object silhouette and at intersections between isophotes from different light sources. We then propagate these 3D normals smoothly along isophotes, and subsequently throughout the interior of the shape. We describe our user interface for editing isophotes and correcting unintended normals produced by our algorithm. We also describe a technique for lifting the generated normal field into a height field given the boundary of the shadow cast by the object. We validate our approach with a perceptual experiment and comparisons to ground truth data. Finally, we present a set of 3D renderings created using our interface.
Flexible G<sup>1</sup> interpolation of quad meshes
2014, Graphical Models
Citation Excerpt :
The meshes were taken from Cindy Grimm’s web site.1 We use either isophotes [35] or global illumination rendering using photon mapping to highlight the visual smoothness of our results. Fig. 17 illustrates many examples with various shapes, curvature behaviors and topological types.
Transforming an arbitrary mesh into a smooth G¹ surface has been the subject of intensive research works. To get a visual pleasing shape without any imperfection even in the presence of extraordinary mesh vertices is still a challenging problem in particular when interpolation of the mesh vertices is required. We present a new local method, which produces visually smooth shapes while solving the interpolation problem. It consists of combining low degree biquartic Bézier patches with minimum number of pieces per mesh face, assembled together with G¹-continuity. All surface control points are given explicitly. The construction is local and free of zero-twists. We further show that within this economical class of surfaces it is however possible to derive a sufficient number of meaningful degrees of freedom so that standard optimization techniques result in high quality surfaces.
Computing parallel curves on parametric surfaces
2014, Applied Mathematical Modelling
Citation Excerpt :
But researchers in the field have identified a list of classical families of curves that qualify as characteristic curves, simply because they account for some well-known properties of the surface. For the visual properties we can use reflection lines [19], highlight lines [20], and isophotes [21], which help to evaluate the behavior and aesthetics of the surface under illumination models, as it is usually done, for instance, in the automotive and aerospace industries. Geometric properties can be analyzed through contour lines [22], lines of curvature [22], geodesic paths [22,23], helical curves [24], asymptotic lines [25], scalar and vector fields [26], etc.
Generating parallel curves on parametric surfaces is an important issue in many industrial settings. Given an initial curve (called the base curve or generator) on a parametric surface, the goal is to obtain curves on the surface that are parallel to the generator. By parallel curves we mean curves that are at a given distance from the generator, where distance is measured point-wise along certain characteristic curves (on the surface) orthogonal to the generator. Except for a few particular cases, computing these parallel curves is a very difficult and challenging problem. In fact, only partial, incomplete solutions have been reported so far in the literature. In this paper we introduce a simple yet efficient method to fill this gap. In clear contrast with other existing techniques, the most important feature of our method is its generality: it can be successfully applied to any differentiable parametric surface and to any kind of characteristic curves on surfaces. To evaluate our proposal, some illustrative examples (not addressed with previous methods) for the cases of section, vector-field, and geodesic parallels are discussed. Our experimental results show the excellent performance of the method even for the complex case of NURBS surfaces.
Dynamic-template processing for passive thermograms: Applied to automotive stamping split detection
2008, NDT and E International
This manuscript introduces a passive thermal-vision modality to detect splits and tears in automotive stampings in real time. This system scans 3D temperature maps of high reflective steel panels, with complex geometry in addition to the drawing die, to locate abnormal temperature readings indicative of high local wrinkling pressure (cause of metal splitting). Preprocessing utilizes a coefficient-correction map to account for the emissivity dependency on part geometries, and the stamping-die changing the thermal profile. Also, a pattern-matching algorithm is used to synchronize the thermal analysis with the die location (stamping pace) through a new concept of matching thermal histograms. A new image-processing routine named “dynamic-template” is developed to retrieve the split's shape and identify its location. The template is computed through a region of interest (ROI) approach with a dynamic threshold, while accounting for spatial deviations (mainly press-line vibration). The developed hardware and software are implemented on an automotive press-line, and the real-time thermal acquisition is processed to illustrate the system performance and success; different split shapes and sizes are detected under actual operating conditions.
Numerical computing of isophote curves, general helices, and relatively normal-slant helices in Minkowski 3-space
2024, Mathematical Methods in the Applied Sciences

View all citing articles on Scopus

View full text

Detecting surface irregularities using isophotes

Abstract

Fuenfachsiges NC-Fraesen gekruemmter Flaechen

Differentialgleichungen, Loesungsmethoden und Loesungen

Correction of local surface irregularities using reflection lines