JPH05324852A - Computer graphics technique - Google Patents

Abstract

PURPOSE:To effectively represent a sharp shadow by calculating the intersection of the border part of the shadow and a mesh by graphic arithmetic processing and setting the mesh along the border part of the shadow. CONSTITUTION:Shape modeling is performed so as to constitute wall surfaces, which constitute an interior space by CAD, with surface models. The surface models which are thus formed are divided into triangular meshes. The direction to the sunshine is decided on the basis of the respective normal directions of the respective meshes, only meshes which do not face the sun are selected, and parallel projection on other meshes which face the sun is performed. The intersections 3S and 3L of the projected meshes and the meshes on which the projection is performed are calculated. Further, the meshes on which the projection is performed are classified by set arithmetic into a project (crossing) part and a difference part. When the product or difference part is triangular, it is set as a new mesh 4S, but when not the part is divided into triangles and set as new meshes 4L.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a computer graphics technique, and more particularly to a computer graphics technique characterized by expressing a sharp shadow using a mesh. INDUSTRIAL APPLICABILITY The present invention can be widely used as a method of predicting the internal light environment of a building or an automobile at the design stage.

[0002]

2. Description of the Related Art Techniques such as ray tracing and the radiosity method have been proposed as means for obtaining highly realistic three-dimensional computer graphics images, and have been put to practical use in various fields as computer performance has improved. The radiosity method was proposed not as a computer graphics drawing method but as an analysis method for quantifying the mutual reflection between the walls in the room. Specifically, the walls forming the analysis space are divided into meshes, and the mutual reflection amount between the walls is calculated based on the geometrical positional relationship between the patches. Computer graphics based on the radiosity method are characterized by high realism because the mutual reflection between the walls is quantified.

[0003]

Although ray tracing can generate a very realistic image and can express a sharp shadow generated by a point light source, it has a problem that it takes too much calculation time. I'm holding. Further, ray tracing is a computer graphics rendering method, and is not suitable for global light environment analysis such as illuminance distribution.

On the other hand, the method of performing mesh division on the wall surface forming the analysis space, such as the radiosity method, is suitable for global light environment analysis, but it is a sharp point light source represented by direct sunlight. It was considered difficult to express the shadow. As a countermeasure for this, it is possible to divide the mesh into smaller pieces, but the increase in calculation time associated with this is a large loss.

The present invention is intended for use in internal light environment analysis of buildings, automobiles, etc., and uses meshes to perform global light environment analysis, and efficiently expresses sharp shadows. It is an object.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above-mentioned object, and calculates the intersection point of the shadow boundary portion and the mesh by the graphic calculation processing to make the mesh the shadow boundary portion. The present invention provides a computer graphics method characterized in that sharp shadows can be clearly expressed by resetting along the same, and particularly a computer graphics method suitable for three-dimensional expression.

Also in the present invention, a mesh division is applied to the wall surface forming the analysis space, as is done by the usual radiosity method. The shape of the mesh is not particularly limited,
A triangular mesh is preferably used. Although the fineness of the mesh is not limited, a coarse mesh is preferably used before the resetting of the mesh described below for the purpose of shortening the calculation time. The roughness of the mesh does not adversely affect the calculation accuracy. The feature of this method is that a sharp shadow can be expressed even with a coarse mesh.

The normal direction of the mesh is determined by each of the apex sequences forming the mesh. Therefore, it is possible to determine whether or not the light emitted from the point light source is facing. A mesh that does not face the light emitted from the light source is selected and projected onto another mesh that faces the light source according to the direction of the light.

The projected mesh is classified into a product (intersection) portion and a difference portion by a two-dimensional set operation of the projected mesh and the projected mesh (projected mesh) on the same plane. The mesh is reset by setting a new mesh for the product / difference portion. Here, the product part becomes the shadow part. A typical example of the present invention will be described below in detail with reference to the flowchart of FIG.

Shape Modeling A wall surface forming an indoor space is constructed by a surface model by CAD, that is, shape modeling is performed.

Mesh setting Each surface model created by shape modeling is divided into triangular meshes, that is, meshes are set. Even if the mesh is made finer in consideration of the calculation time, it is possible to generate a sharp shadow.

Setting of Light Source Calculation was carried out with the point light source as the sun. In this case, the light emitted from the light source is parallel light.

Selection of mesh not facing the sun The direction of the sun is determined based on the normal direction of each mesh, and only the mesh not facing the sun is selected and other meshes facing the sun are selected. Parallel projection to.

Set Operation If the projected mesh and the projected mesh intersect each other, the intersection of the two is calculated. Further, the mesh projected by the set operation is classified into a product (intersection) part and a difference part.

Resetting the mesh If the product or difference in the set operation is a triangle, set them as a new mesh, and if they are not triangles, divide them into triangles and set them as a new mesh. .. FIG. 2 shows the mesh before being reset, and FIG. 3 shows the mesh after being reset. That is, FIG. 2 and FIG.
1 is an element, 2 is a node, 5 is a boundary of a shadow, S is a shadow part, and L is a sunshine part. In FIG. 3, 3S, 3L
Is an intersection calculated along the boundary of the shadow, and the mesh is reset by using these as new nodes. Note that 3S and 3L are separated for ease of understanding,
Actually, both are on the same coordinate. Further, in FIG. 3, 4S and 4L are elements newly generated by resetting the mesh.

Illuminance Calculation After resetting the mesh, the direct sunlight illuminance at each node of the mesh is calculated. The direct sunlight illuminance is calculated by the calculation formula shown in Formula 1. In formula 1, Ed: sunlight illuminance at the node, Edn: direct sunlight from the normal surface, ti: visible light transmittance for each incident angle of the visible light-transmitting wall that blocks direct sunlight, φ: direct sunlight incident angle to the node is there.

[0017]

[Equation 1]

Rendering by Z-buffer By performing rendering by the Z-buffer according to the sunlight illuminance at each node of the mesh, it is possible to generate a three-dimensional computer graphics image having a sharp shadow even by the method using the mesh. It will be possible.

Conventionally, in order to express a sharp shadow by a method using a mesh, a method of making a mesh fine has been dealt with, but in the present method, a sharp shadow is expressed even with a coarse mesh. Have a unique characteristic. Further, since a mesh is used, the drawing speed when the viewpoint changes, for example, also has an overwhelming advantage over ray tracing which can express a sharp shadow.

[0020]

EFFECTS OF THE INVENTION According to the present invention, it is possible to efficiently express a sharp shadow due to a point light source represented by direct sunlight by a mesh, which has been difficult in the global light environment analysis using a mesh. Became. This technique
Since the mesh division is premised, it is possible to easily connect the analysis result to highly realistic three-dimensional computer graphics. In particular, in fields where global light environment analysis is required, such as architecture and automobiles, there is a great merit that efficient three-dimensional computer graphics can be efficiently generated.

[Brief description of drawings]

FIG. 1 is a flowchart showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a state of a mesh before resetting of the mesh.

FIG. 3 is an explanatory diagram showing a state of a mesh after resetting of the mesh.

[Explanation of symbols]

 1: Element 2: Node 3S, 3L: Intersection calculated along the boundary of the shadow 4S, 4L: Element generated by resetting the mesh 5: Boundary of the shadow

Claims (1)

[Claims] 1. An intersection of a shadow boundary and a mesh is calculated,
A computer graphics method characterized in that sharp shadows can be clearly expressed by resetting the mesh along the boundary of the shadow by a set operation.