Ulrich Krispel

Irregular lattices for complex shape grammar facade parsing

High-quality urban reconstruction requires more than multi-view reconstruction and local optimization. The structure of facades depends on the general layout, which has to be optimized globally. Shape grammars are an established method to express hierarchical spatial relationships, and are therefore suited as representing constraints for semantic facade interpretation. Usually inference uses numerical approximations, or hard-coded grammar schemes. Existing methods inspired by classical grammar parsing are not applicable on real-world images due to their prohibitively high complexity. This work provides feasible generic facade reconstruction by combining low-level classifiers with mid-level object detectors to infer an irregular lattice. The irregular lattice preserves the logical structure of the facade while reducing the search space to a manageable size. We introduce a novel method for handling symmetry and repetition within the generic grammar. We show competitive results on two datasets, namely the Paris 2010 and the Graz 50. The former includes only Hausmannian, while the latter includes Classicism, Biedermeier, Historicism, Art Nouveau and post-modern architectural styles.

A GML shape grammar for semantically enriched 3D building models

The creation of building and facility models is a tedious and complicated task. Existing CAD models are typically not well suited since they contain too much or not enough detail; the manual modeling approach does not scale; different views on the same model are needed, and different levels of detail and abstraction; and finally, conventional modeling tools are inappropriate for models with many internal parameter dependencies. As a solution to this problem we propose a combination of a procedural approach with shape grammars. The model is created in a top-down manner; high-level changeability and re-usability are much less of a problem; and it can be interactively evaluated to provide different views at runtime. We present some insights on the relation between imperative and declarative grammar descriptions, and show a detailed case study with facility surveillance as a practical application. Display Omitted Research Highlights? Simple shape grammar formalism based on GML. ? Example reconstruction of large-scale facility with interiors. ? Discussion of imperative vs. declarative grammar description paradigms. ? Semantic enrichment with annotations for semantic queries

A Survey of Algorithmic Shapes

In the context of computer-aided design, computer graphics and geometry processing, the idea of generative modeling is to allow the generation of highly complex objects based on a set of formal construction rules. Using these construction rules, a shape is described by a sequence of processing steps, rather than just by the result of all applied operations: shape design becomes rule design. Due to its very general nature, this approach can be applied to any domain and to any shape representation that provides a set of generating functions. The aim of this survey is to give an overview of the concepts and techniques of procedural and generative modeling, as well as their applications with a special focus on archeology and architecture.

Deformation-Aware Split Grammars for Architectural Models

With the current state of video games growing in scale, manual content creation may no longer be feasible in the future. Split grammars are a promising technology for large scale procedural generation of urban structures, which are very common in video games. Buildings with curved parts, however, can currently only be approximated by static pre-modeled assets, and rules apply only to planar surface parts. We present an extension to current split grammar systems that allows the generation of curved architecture through free-form deformations that can be introduced at any level in a grammar. Further subdivision rules can then adapt to these deformations to maintain length constraints, and repetitions can adjust to more or less space.

Constructive Roof Geometry

While the growing demand for new building models contained in virtual worlds, games, and movies, makes the easy and fast creation of modifiable models more and more important, 3D modeling of buildings can be a tedious task due to their sometimes complex geometry. For historic buildings, especially the roofs can be challenging. We present a new method of combining simple building solids to form more complex buildings, and give an emphasis on the blending of roof faces. This can be integrated in common pipelines for procedural modeling of buildings and will bring more expressiveness than existing methods.

Compilation of procedural models

Scripting techniques are used in various contexts. The field of application ranges from layout description languages (PostScript), user interface description languages (XUL) and classical scripting languages (JavaScript) to action nodes in scene graphs (VRMLScript) and web-based desktop applications (AJAX). All these applications have an increase of scripted components in common -- especially in computer graphics. As the interpretation of a geometric script is computationally more intensive than the handling of static geometry, optimization techniques, such as just-in-time compilation, are of great interest. Unfortunately, scripting languages tend to support features such as higher order functions or self-modification, etc. These language characteristic are difficult to compile into machine/byte-code. Therefore, we present a hybrid approach: an interpreter with an integrated compiler. In this way we speed up the script evaluation without having to remove any language features e.g. the possibility of self-modifications. We demonstrate its usage at XGML -- a dialect of the generative modeling language GML, which is characterized by its dynamic behavior.

Geometry simplification according to semantic constraints

The building industry and facility management is in a state of upheaval: The complexity of the real world is now represented in its digital counterpart. The established object-based file format “Industrial Foundation Classes (IFC)” developed by the International Alliance for Interoperability facilitates interoperability in the context of Building Information Modeling. Unfortunately, there is no feasible workflow for filtering energy-related information, e.g. a streamlined version of the building geometry. Simplification methods often fail on CAD data that is ignorant of domain specific semantic information (i.e. functional differences between a door and stucco are not reflected in the geometry and are therefore often ignored). With EU law now requiring energy performance certificates to be issued for all buildings, energy performance analysis becomes an increasingly important topic. Accurate, yet efficient calculation depends on simple building models. However, typical IFC models contain a lot of irrelevant data, in particular geometric representations, which are too detailed for energy performance analysis. Therefore, we propose an algorithm that extracts input models suitable for calculations directly from IFC models in a semi-automatic process. The key aspect of the algorithm is geometry simplification subject to semantic and functional groups; more specifically, the 3D representations of walls, slabs, windows, doors, etc. are reduced to a collection of surfaces describing the building’s thermal shell on one hand, and the material layers associated with it on the other hand. This simplification takes into account semantic constraints and expert knowledge. Furthermore, it works on “real-world” data; i.e. it is robust towards incomplete, imperfect and inconsistent data.

Constructive Roofs from Solid Building Primitives

The creation of building models has high importance, due to the demand for detailed buildings in virtual worlds, games, movies and geo information systems. Due to the high complexity of such models, especially in the urban context, their creation is often very demanding in resources. Procedural methods have been introduced to lessen these costs, and allow to specify a building or a class of buildings by a higher level approach, and leave the geometry generation to the system. While these systems allow to specify buildings in immense detail, roofs still pose a problem. Fully automatic roof generation algorithms might not yield desired results especially for reconstruction purposes, and complete manual specification can get very tedious due to complex geometric configurations. We present a new method for an abstract building specification, that allows to specify complex buildings from simpler parts with an emphasis on assisting the blending of roofs.

Dynamo - dynamic 3D models for the web: a declarative approach to dynamic and interactive 3D models on the web using x3dom

Animations aid greatly to a presentation of a sophisticated man-made object. With additional interactivity, a user can explore such an object to gain even better understanding. The authoring of such dynamic models is often very resource demanding, as the animations and logic of interaction has to be expressed in an authoring program; often using a programming language. Furthermore, the 3D model and its dynamic capabilites are tightly coupled, which makes it costly to integrate changes of the underlying 3D model - e.g. if a machine part changes. Contribution and Benefit. We present a novel scheme to define varying states of a 3D model in a decoupled, declarative manner using pattern matching. Furthermore, we demonstrate its capabilites for the web with an open source JavaScript implementation that operates on an x3dom model.