htrdr-obj.5 (3117B)
1 .\" Copyright (C) 2018-2019, 2022-2025 Centre National de la Recherche Scientifique 2 .\" Copyright (C) 2020-2022 Institut Mines Télécom Albi-Carmaux 3 .\" Copyright (C) 2022-2025 Institut Pierre-Simon Laplace 4 .\" Copyright (C) 2022-2025 Institut de Physique du Globe de Paris 5 .\" Copyright (C) 2018-2025 |Méso|Star> (contact@meso-star.com) 6 .\" Copyright (C) 2022-2025 Observatoire de Paris 7 .\" Copyright (C) 2022-2025 Université de Reims Champagne-Ardenne 8 .\" Copyright (C) 2022-2025 Université de Versaille Saint-Quentin 9 .\" Copyright (C) 2018-2019, 2022-2025 Université Paul Sabatier 10 .\" 11 .\" This program is free software: you can redistribute it and/or modify 12 .\" it under the terms of the GNU General Public License as published by 13 .\" the Free Software Foundation, either version 3 of the License, or 14 .\" (at your option) any later version. 15 .\" 16 .\" This program is distributed in the hope that it will be useful, 17 .\" but WITHOUT ANY WARRANTY; without even the implied warranty of 18 .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 19 .\" GNU General Public License for more details. 20 .\" 21 .\" You should have received a copy of the GNU General Public License 22 .\" along with this program. If not, see <http://www.gnu.org/licenses/>. 23 .Dd October 5, 2023 24 .Dt HTRDR-OBJ 5 25 .Os 26 .Sh NAME 27 .Nm htrdr-obj 28 .Nd geometric file format 29 .Sh DESCRIPTION 30 A 31 .Nm 32 file is an ordinary obj file composed solely of triangular meshes. 33 Its special feature is that each triangle must be included in a material 34 group as defined by the 35 .Li usemtl 36 directive. 37 And the form of the 38 .Li usemtl 39 directive must be as follows: 40 .Bd -ragged -offset Ds 41 .Li usemtl Va front_mtl Ns Oo : Ns Va interface_mtl Oc : Ns Va back_mtl 42 .Ed 43 .Pp 44 with 45 .Va front-mtl , 46 .Va interface-mtl 47 and 48 .Va back-mtl 49 the material names of the front, interface and back of the triangles 50 belonging to the group. 51 The interface material name is optional: it is used for thin geometries, 52 i.e. geometries with no thickness. 53 Material names can be composed of any character, with the exception of 54 spaces, tabs and the colon character used to separate the 55 aforementioned names. 56 Note that, by convention, a side of a triangle is said to be 57 "front-facing" when its vertices are ordered clockwise. 58 .Pp 59 The grammar of a 60 .Nm htrdr-obj 61 file is therefore a subset of the obj file format, with only one 62 specific convention concerning material names. 63 Consequently, any software supporting the obj file format can be used to 64 create or view a 65 .Nm 66 file. 67 .Sh EXAMPLES 68 Define a sheet of paper at the interface between air and concrete: 69 .Bd -literal -offset Ds 70 v -1.0 -1.0 0 71 v -1.0 1.0 0 72 v 1.0 -1.0 0 73 v 1.0 1.0 0 74 75 usemtl air:paper:concrete 76 f 1 2 3 77 f 3 2 4 78 .Ed 79 .Pp 80 Define a wooden cube whose faces along the Z axis are against a brick. 81 The other faces are in contact with the air: 82 .Bd -literal -offset Ds 83 v 0 0 0 84 v 1 0 0 85 v 0 1 0 86 v 1 1 0 87 v 0 0 1 88 v 1 0 1 89 v 0 1 1 90 v 1 1 1 91 92 usemtl wood:air 93 f 1 3 2 94 f 2 3 4 95 f 1 5 3 96 f 3 5 7 97 f 5 6 7 98 f 7 6 8 99 f 4 8 2 100 f 2 8 6 101 102 usemtl wood:brick 103 f 3 7 4 104 f 4 7 8 105 f 1 2 5 106 f 5 2 6 107 .Ed 108 .Sh HISTORY 109 The 110 .Nm 111 format was first developed for the 112 .Xr htrdr 1 113 program.