Global overlap analysis

Detecting minimal overlaps with ARTIST STUDIO

Author: Herbert Heppner, Team Lead Software Technology / Publish date 18.12.2025

When working with larger or non-rectangular patches, users often need to precisely control local overlaps to ensure full surface coverage. Although laminate imperfections caused by draping effects or placement tolerances are typically very small in Fiber Patch Placement, narrow safety margins may require a detailed analysis of the laminate. In these cases, it is important to verify that minimum overlap requirements between adjacent patches are consistently met and that no small gaps remain hidden within the laminate.

To support this task, ARTIST STUDIO now includes a dedicated global overlap analysis feature. It provides a reliable evaluation of overlap quality across the entire lay-up. This enables users to quickly identify and resolve critical areas, ensuring robust laminate quality even for demanding geometries. In the example below, patches with insufficient overlap are highlighted in light red color, and the corresponding failing edges are marked accordingly. There is a single gap inside the laminate, formed by three patches and another gap at the boundary that is associated with the edges of two patches. 

Another example shows the results for the same part after the previously identified gaps have been closed. In this case, however, the required minimum overlap was increased from 1 mm to 7 mm. Two edges are still highlighted because their local geometry results in an overlap of only 6.12 mm. This exact value can be retrieved from the results dialog. By clicking on a result, the corresponding patch will be highlighted for efficient analysis.

Why conventional overlap measurements fail 

To introduce the topic, it is helpful to first consider a straightforward and intuitive approach to evaluating overlaps: measuring the maximum 3D distance between corresponding patch edges. For certain well-defined geometries, this method can deliver acceptable results. In some cases, it is even possible to automate the identification of matching edge pairs and evaluate their mutual distances. The example below illustrates this naïve approach to overlap measurement. 

However, there are many situations where an automated edge-based algorithm will fail – and even manual selection of “corresponding” edges becomes impractical. The examples below demonstrate that defining overlap through (nearly) parallel edges is inherently ambiguous (left). This edge-to-edge approach becomes completely unsuitable once patches have arbitrary shapes or overlap at non-orthogonal angles (right). For complex 3D surfaces, where patches may exhibit significant curvature or appear almost folded, further issues arise that are not even reflected in these simplified cases.

These limitations prompted our software team to question whether edge-to-edge distance measurements truly address the underlying problem. The core challenge becomes clear in the next example: multiple neighboring patches (N1–N5) overlap a central target patch. None of the neighbors fully overlaps one of the target patch’s edges – a situation that is very typical, especially when working with patches of constant shape. Additionally, a global gap becomes visible. Based on the previously described edge-to-edge definition, how would it be possible to ensure that the target patch is sufficiently overlapped on all sides?

Ultimately, any solution must be robust enough to guarantee that, once users specify an admissible overlap range, the system reliably detects every violation – ensuring full laminate integrity and eliminating the risk of hidden coverage gaps.   

A practical method for universal overlap measurement

Our solution to this challenge begins with transforming the 3D problem into a 2D one, as illustrated below. 

By projecting all neighboring patches onto the target patch – the patch currently being evaluated – the algorithm significantly reduces geometric complexity. Multiple overlapping regions are merged into simplified polylines that accurately represent how the surrounding laminate interacts with the target patch. Once projected, this polyline is mapped onto the internal 2D coordinate system of the target patch. This greatly simplifies both the computational analysis and the user’s interpretation of the results.

It is important to note that the approximation only needs to be accurate inside the patch boundary; the algorithm does not consider regions extending beyond the target patch. As shown in the right-hand figure, this approach makes it straightforward to identify unprotected openings within the merged overlap region. For a complete laminate assessment, this projection and polyline analysis is carried out individually for every patch based on its respective neighbors.

A second key question, however, still needed to be addressed: How can we define overlap distance universally and consistently for any FPP laminate? The breakthrough came from addressing the target patch and not the neighboring patches. 

The central image above illustrates the merged overlap boundary of all neighboring patches around the green target patch. The dotted polyline represents the combined boundaries, while the gray area indicates the part of the target patch that is effectively overlapped by neighboring patches. Because this polyline can form highly irregular shapes, a direct overlap measurement is not feasible.

Instead, as shown in the rightmost image, the shape of the target patch is offset inward in multiple steps. For each increment, the system checks whether the currently offset target patch polyline intersects the neighborhood polyline. As soon as an intersection is detected, the algorithm has identified the minimum overlap distance for that specific patch.

This method provides a robust and universal definition of overlap that is suitable for complex 3D laminates, ensuring that any violation of the admissible overlap range is reliably detected. 

Integrating surface boundaries into overlap analysis

The presented approach not only evaluates patch-to-patch overlaps but also accounts for patch-to-boundary overlaps. This is essential for maintaining a consistent laminate thickness when placing patches along the outer edges of a part. As shown in the figure below, the part boundary is projected onto the target patch in the same way as neighboring patches. The projected boundary is then inverted and merged with the internal overlap polygons generated by neighboring patches. Once this combined polyline is created, the remaining analysis follows the same procedure as previously described.

Note: Support for arbitrary boundaries is currently available as a beta feature. In particular, boundaries consisting not only of straight edges may result in limitations in overlap detection, including potential false-positive and false-negative classifications

Why local overlaps matter in large patch FPP

Ten years ago, Fiber Patch Placement primarily relied on small, rectangular patches – often hundreds or even thousands per laminate. The shape of each patch played only a minor role; the key design challenge was optimizing the overlaps between the many patches by shifting their position.

Today, we refer to this approach as Small Patch FPP, which naturally implies the existence of its counterpart: Large Patch FPP. This newer concept focuses on significantly fewer but individually tailored, larger patches. The figure below illustrates the fundamental differences between both approaches.

With Large Patch FPP, the relevance of local patch-to-patch overlaps increases substantially. Unlike small-patch lay-ups – where overlap patterns tend to average out – the performance and reliability of large-patch laminates depend heavily on the precise definition and control of each overlap. Our previously existing overlap analysis tools were originally developed for Small Patch FPP and optimized for evaluating overlap along the fiber direction to enhance mechanical performance. However, they were not designed for accurately measuring overlaps – especially in the transverse direction – or for handling the irregular shapes characteristic of tailored large patches.
This makes the development of a general, robust overlap definition a nontrivial challenge when working with large, variable patch geometries.

Precise lay-up on double-curved surfaces and impact on weight-critical composite applications

There is no other technology on the market that is able to efficiently place composite material plies onto double curved surfaces. Cevotec achieves tight tolerances through optimal integration of hardware (SAMBA production systems) and CAD/CAM software (ARTIST STUDIO).

Aerospace applications often require weight minimization on double-curved surfaces. For components requiring full surface coverage with a single patch layer, this necessitates minimizing overlaps and precisely controlling the overlap window.