XL4C4D - Adding the Graph Transformation Language XL to CINEMA 4D

A plug-in for the 3D modeling application CINEMA 4D is presented which allows to use the graph transformation language XL to transform the 3D scene graph of CINEMA 4D. XL extends Java by graph query and rewrite facilities via a data model interface, the default rewrite mechanism is that of relational growth grammars which are based on parallel single-pushout derivations. We illustrate the plug-in at several examples, some of which make use of advanced 3D features

Realization and Extension of the Xfrog Approach for Plant Modelling in the Graph-Grammar Based Language XL

Two well-known approaches for modelling virtual vegetation are grammar-based methods (L-systems) and the Xfrog method, which is based on graph transformations expanding "multiplier" nodes. We show that both approaches can be unified in the framework of "relational growth grammars", a variant of parallel graph grammars. We demonstrate this possibility and the synergistic benefits of the combination of both methods at simple plant models which were processed using our open-source software GroIMP

Parallel Graph Grammars with Instantiation Rules Allow Efficient Structural Factorization of Virtual Vegetation

Parallel rewriting of typed attributed graphs, based on the single-pushout approach extended by connection transformations, serves as the backbone of the multi-paradigm language XL, which is widely used in functional-structural plant modelling. XL allows to define instantiation rules, which enable an instancing of graphs at runtime for frequently occurring substructures, e.g., in 3-d models of botanical trees. This helps to save computer memory during complex simulations of vegetation structure. Instantiation rules can be called recursively and with references to graph nodes, thus providing a unifying formal framework for various concepts from the literature: object instancing, structural factorization, Xfrog multiplier nodes, L-systems with interpretation. We give simple examples and measure the computation time for an idealized growing virtual plant, taken from the GreenLab model, in its implementation with instantiation rules in XL, compared to a version without instantiation rules

Growth grammars simulating trees – an extension of L-systems incorporating local variables and sensitivity.

The rule-based formal language of ‘stochastic sensitive growth grammars’ was designed to describe algorithmically the changing morphology of forest trees during their lifetime under the impact of endogenous and exogenous factors, and to generate 3-D simulations of tree structures in a systematic manner. The description in the form of grammars allows the precise specification of structural models with functional components. These grammars (extended L-systems) can be interpreted by the software GROGRA (Growth grammar interpreter) yielding time series of attributed 3-D structures representing plants. With some recent extensions of the growth-grammar language (sensitive functions, local variables) it is possible to model environmental control of shoot growth and some simple allocation strategies, and to obtain typical competition effects in tree stands qualitatively in the model

CT-Based Attenuation Correction in I-123-Ioflupane SPECT

Purpose Attenuation correction (AC) based on low-dose computed tomography (CT) could be more accurate in brain single-photon emission computed tomography (SPECT) than the widely used Chang method, and, therefore, has the potential to improve both semi-quantitative analysis and visual image interpretation. The present study evaluated CT-based AC for dopamine transporter SPECT with I-123-ioflupane. Materials and methods Sixty-two consecutive patients in whom I-123-ioflupane SPECT including low-dose CT had been performed were recruited retrospectively at 3 centres. For each patient, 3 different SPECT images were reconstructed: without AC, with Chang AC and with CT-based AC. Distribution volume ratio (DVR) images were obtained by scaling voxel intensities using the whole brain without striata as reference. For assessing the impact of AC on semi-quantitative analysis, specific-to-background ratios (SBR) in caudate and putamen were obtained by fully automated SPM8-based region of interest (ROI) analysis and tested for their diagnostic power using receiver-operator- characteristic (ROC) analysis. For assessing the impact of AC on visual image reading, screenshots of stereotactically normalized DVR images presented in randomized order were interpreted independently by two raters at each centre. Results CT-based AC resulted in intermediate SBRs about half way between no AC and Chang. Maximum area under the ROC curve was achieved by the putamen SBR, with negligible impact of AC (0.924, 0.935 and 0.938 for no, CT-based and Chang AC). Diagnostic accuracy of visual interpretation also did not depend on AC. Conclusions The impact of CT-based versus Chang AC on the interpretation of I-123-ioflupane SPECT is negligible. Therefore, CT-based AC cannot be recommended for routine use in clinical patient care, not least because of the additional radiation exposure

Towards universality of growth grammars: Models of Bell, Pagès, and Takenaka revisited

"Growth grammars" are extended parametric Lindenmayer systems, enriched by some novel features (expand operator, global sensitivity, interpretive rules, arithmetical-structural operators). They can serve as a formal basis for describing functional-structural plant models from the literature. This is demonstrated on three well-known models having in common that they were originally developed without using any formal grammars: an early, but quite general structural plant simulator by Bell, a root model by Pagès and Kervella, and an above-ground tree model (involving competition for light) by Takenaka. The study considers the special extensions of L-systems necessary to rebuild some characteristic features of each of these models. The obtained degree of universality and the current limitations of the growth-grammar approach with respect to functional-structural tree models are discussed.Vers l'universalité des grammaires de croissance : une nouvelle rencontre entre les modèles de Bell, Pagès et Takenaka. Les "grammaires de croissance" sont une version étendue de systèmes de Lindenmayer paramétrisés, élargi par quelques propriétés nouvelles (opérateur d'expansion, sensitivité globale, règles interprétatives, opérateurs arithmétiques-structuraux). Ils peuvent servir comme une base formelle pour la déscription de modèles fonctionnels-structuraux déjà publiés. Cette possibilité est démontrée par trois modèles bien connu qui ont en commun la qualité d'être développé sans utilisation de quelque grammaire formelle : un simulateur structural des plantes de Bell, un modèle de racines de Pagès et Kervella, et un modèle d'arbre sur-sol (inclus la concurrence pour la lumière) de Takenaka. Cette étude considère les extensions spéciales de L-systèmes qui sont nécessaire pour reconstruire quelques propriétés caractéristiques de chacun de ces modèles. Le degré d'universalité obtenu et les limitations actuelles de l'approche de grammaires de croissance en relation avec les modèles fonctionnels-structuraux d'arbre sont discutées

Specification of morphological models with L-systems and relational growth grammars

Among the techniques for the creation of photorealistic virtual organisms, particularly plants, and in scientific models of vegetation structure, rule-based specifications (formal grammars) play a prominent role. Lindenmayer systems (L-systems) are the most widespread formalism of this sort, but certain types of graph grammars, combined with standard object-oriented programming, offer even more possibilities to specify ruledriven developments of 3-dimensional arrangements, morphology of virtual organisms and underlying processes like, e.g., metabolic reactions. Examples of grammar rules and the virtual geometrical structures generated from them, all realizable with the open-source software GroIMP (www.grogra.de), are shown. This grammar-based approach is often not directly used for the specification of a picture as a pattern of graphical elements in a plane, but for virtual 3-dimensional scenes, which are then rendered visible using standard techniques of geometry-based computer graphics. 1. Introduction: Rule-based modelling of development The programme for a computer-based simulation of a process is often specified by writin