3D model modeling specification
All the digital models mentioned in this article are made with 3D MAX. Even if the driving engines are different, the requirements for the models are basically the same. When a VR model is completed, the basic content it contains includes: scene size, unit, model classification collapse, naming, node editing, texture, coordinates, texture size, texture format, shader, etc. must conform to the production specification . A model file with clear classification, reduced number of faces, and standardized production is very necessary for program control management.
First, a brief introduction to the production process: material collection - model production - texture production - scene collapse, naming, UV coordinates - lighting rendering test - scene baking - scene adjustment and export.
Chapter 1, Model Making Specifications
1. Before model division, the model positioning standard must be determined. Usually this standard will be a CAD base map. The production personnel must determine the model position of their own division of labor according to the file with the CAD base map, and shall not make any modifications to this standard file. The CAD base map imported into MAX is preferably at (0, 0, 0) position, so that the initial model of the producer is near the zero point.
2. Unless otherwise specified, the unit is Meters.
3. Delete the redundant faces in the scene. When building the model, you don’t need to model the invisible places, and you can also delete the invisible faces. The main purpose is to improve the utilization of textures and reduce the number of faces in the entire scene to improve interaction. The speed at which the scene runs. Such as the bottom of the box, the back of the object attached to the wall, etc.
4. Keep the distance between the model faces. The recommended minimum distance is 1/2000 of the maximum scale of the current scene. For example: when making an indoor scene, the distance between the surfaces of the object should not be less than 2mm; when making an outdoor scene with a length (or width) of 1km, the distance between the surfaces of the object should not be less than 20cm. If the surface of the object is too close to each other, there will be a flickering phenomenon between the two surfaces alternately. Coplanar, leaky and reverse surfaces are not allowed between models, and invisible surfaces must be deleted. At the early stage of modeling, we must pay attention to check the coplanar, leaky and reverse situations.
5. Copy the objects that can be copied as much as possible. If an object with 1,000 faces is baked and copied 100 times, then the resources it consumes are basically the same as the resources consumed by an object.
6. It is best to use Editable Poly mesh modeling when modeling. This modeling method will not appear triangular surfaces during final baking. If Editable Mesh is used, triangular surfaces may appear during final baking.
7. The collapse of the model When a building model is modeled and textured, the model is then collapsed. This step is also a preparation for the next step of baking. So pay attention to some problems when collapsing:
(1) Collapse according to the principle of "one building, one object". If the volume is particularly large or the conjoined building can be divided into 2-3 objects, but before exporting, it must be collapsed into one object according to the building, and the village in the city must be collapsed according to the courtyard .
(2) Use Box to invert the collapsed object and switch to Poly mode. At this time, you need to check whether the texture is disordered;
(3) For collapsed objects, collapse according to buildings or plots, and do not collapse across regions;
(4) Carry out strict standard naming according to the requirements of the project on the name;
(5) The center of mass of all objects should be attributed to the center, and the object is locked after checking that the position of the object is correct;
Remarks: All objects are not allowed to have more than 20,000 triangular faces, otherwise an error will occur when exporting.
8. Name the model. Chinese names cannot be used, and English names must be used, otherwise there will be problems in the English system. The building model of the plot is not allowed to have the same name, and must be named according to the specification.
9. The planting method of the tree is a cross tree or a simple model tree. When planting trees, the relationship with the surrounding buildings should be taken into consideration. Trees should not be planted indiscriminately, but different tree species and positions should be placed according to the current situation; simple model trees should be planted in key building plots, and crosses should be planted on the corresponding places. Slice tree (for replacement); when exporting, the model tree and the corresponding cross-slice tree are a single tree, and other cross-slice trees can be collapsed together, but the number of faces cannot exceed 10,000.
10. The level of the model is the fineness of the model. Sometimes when we model, we have to judge the accuracy of the simulation model based on the specific location and importance of the building. Buildings can be classified into five levels. Among them, level one is the highest level, and level five is the lowest level. The number of faces of a single object should not be too large, after all, it is for virtual reality, not for making a single rendering. The number of faces of a single object should be controlled below 8000 faces.
11. Mirrored objects need to be corrected. To create a new model by mirror copying, you need to add a modification editor to correct it.
Step 1: You need to select the mirrored object, then enter the Utilities panel, click Reset XForm, and then click Reset Selected; Step 2: Enter the modfiy panel, select the Normal command, and reverse the normal.
12. The solution to the black seam of the baked object. When baking, if the picture is not large enough, black seams will often appear on the edges. Handling tips:
1) If it is more complicated to make a bird's-eye view of the building, you can merge the building into one object to become multiple materials, and then fully bake the building as a whole; this can save a lot of resources.
2) For buildings and terrains, it is necessary to check the tile ratio of the texture material of the model. For the far surface (or grass), you can consider using a realistic map to tile, and the number of tiles is less. For the ground material at the far end, if the number of tiles is large, the sense of reality will be poor.
Chapter 2, Material Mapping Specifications
1. Material and map types. We are currently using Unity3D software as the simulation development platform. This software has some special requirements for the material of the model. In the 3dsMax we use, not all materials are supported by Unity3D software. Only the following materials are supported by Unity3D software. support. Standard (standard material) The default general shader. Basically all current simulation systems support this material type. Multi/Sub-Object (multi-dimensional/sub-object material) combines multiple materials into a composite material, which is assigned to different sub-object selection levels of an object. It should be noted that in the production of VR scenes, the sub-materials in the Multi/Sub-Object material must be Standard standard materials. Otherwise it is not supported by unity3d. We must collapse all the objects together before making the model for baking textures, and the collapsed new object will automatically generate a new Multi/Sub-Object multi-dimensional/sub-object material. Therefore, this material type is often used in our simulation productions.
2. Texture channel and texture type. Unity3D currently only supports the Bitmap texture type, and all other texture types do not support it. Only Diffuse Color (diffuse reflection) and self-Illumination (self-illumination, used to export lightmap) texture channels are supported. After the Self-Illumination (opaque) texture channel bakes the lightmap, you need to set the channel of this texture channel as the new channel after baking, and point the generated lightmap to self-Illumination.
3. The file format and size of the texture. The original texture of the building is JPG without channels, and 32-bit TGA with channels, but the maximum size should not exceed 2048; the texture file size must be 2 to the Nth power (8, 16, 32, 64, 128, 256, 512) , the maximum texture size cannot exceed (1024×1024). Save texture maps as TGA format when baking.
4. Texture and material application rules
(1) Textures cannot be named in Chinese, and cannot have the same name;
(2) The name of the shader is consistent with the name of the object;
(3) The naming of the parent-child hierarchy of the shader must be consistent;
(4) The same type of texture must use a shader;
(5) Except for objects that need to be represented by double-sided materials, other objects cannot use double-sided materials;
(6) The ID number of the shader must be consistent with the ID number of the object.
(7) If you use CompleteMap to bake, a Shell material will be automatically generated after baking, and the Shell material must be changed to Standard standard material, and the channels must be consistent, otherwise the texture cannot be exported correctly.
(8) Textures with an Alpha channel must be named with _al to distinguish them.
5. Channel texture application rules. When the model needs to be processed through channels, it is necessary to make textures with channels. When making the channel texture of the tree, it is best to change the transparent part to the main color of the tree, so that the color of the effective edge part can be correct when rendering. Channel textures take up more resources than ordinary textures of the same size during program rendering. Channel texture names should end with -AL.
Chapter 3, Model Baking and Export
model baking
1. Scene lighting
(1) Rendering method: Use the Light Tracer ray tracing that comes with Max for rendering.
(2) Lighting effect control: This project will give a fixed baking light before baking. The height, angle and parameters of the light cannot be adjusted. You can move the light group to your own block in the top view. You must use the light Merge scenes and bake.
2. Baking texture method There are two baking methods for architectural models: one is LightMap baking and pasting method, and the texture rendered by this kind of baked map only has shadow information and does not contain basic textures. Specifically applied to the production of model files with clearer textures (such as terrain), the principle is to superimpose the basic texture map of the model and the LightMap shadow map. The advantage is that the texture of the final model is relatively clear, and repeated texture maps can be used to save texture resources; the baked model can be directly exported to FBX files without modifying the map channel. The disadvantage is that the LightingMap texture does not contain highlight information; the other is the CompleteMap baking method. The advantage of this baked texture method is that the rendered texture itself has basic texture and light and shadow information, but the disadvantage is that there is no detail texture, and it is near Textures are blurry at times.
3. Baked map settings
①CompleteMap baking method When setting CompleteMap baking, you should pay attention to the following points:
a) The texture channel and object UV coordinate channel must be 1 channel;
b) The storage format of baked texture files is TGA format;
Use the existing channel, the default is 3, and the shadow participates in the baking calculation to create a new Baked material file format type, the target map column.
② The LightingMap baking method is different from the CompleteMap setting when performing the LightingMap baking setting:
a) The texture channel and object UV coordinate channel must be 3 channels;
b) The shadow mode of the light during baking is Adv.RayTraced shadow;
Create a new Baked material, enable direct lighting and shadows to participate in baking calculations, and enable indirect lighting. The target map column file format type uses existing channels, and the default is 3.
c) When baking with LightingMap, the background color should be changed to white to avoid black edges; while baking with CompleteMap, the background color should be changed to a color similar to the texture.
d) After baking with lightmap, you need to change the material back to Standard, then copy the newly generated map to Standard's self-Illumination, and set the correct texture channel.
4. Texture UV editing must be done manually. Model export
1. Change the baked shader to a standard shader, set the channel to 1, and set the self-illumination to 100;
2. Keep all object names, shader names, and texture names consistent
3. Merge vertices (the size should be appropriate);
4. Clear the scene, delete all objects except the main useful objects;
5. Clear the shader and delete the redundant shader (unimportant textures should be reduced);
6. Export fbx as required (check to see if you want to group and export);
Export actions as the case may be
Chapter 4, Scenario Model Acceptance Model Production Process Model Acceptance Process Model Acceptance Criteria
Chapter 5, Model Backup
Submit standard documents
Standard backup mode:
l. UV coordinates: store the UV coordinates edited before the terrain type and building baking;
2. Export fbx: store the final exported terrain and building fbx files;
3. Baking map: store the final map of the terrain and the final baking map of the building, in tga format, and there is a converted map in it;
4. Original textures: store all the textures of landforms and buildings during the production process;
5. Max file: the original model, without any collapse, the file with UVW map coordinates. Before baking, the model has been collapsed, the UV has been developed, and the light rendering test file has been debugged. The baked model is a file that has been baked without any processing. Exported the model, processed the baked objects, merged the vertices, and deleted all the files of useless objects.
Chapter 6, Project Naming Requirements (Refer to the Modeling Specification Items.docx document for details)
1. Building model naming: area name_jz_number; such as: SH01_01_jz_01, SH01_01_jz_02...
2. Naming of architectural textures: model name_number; such as: SH01_01_jz_01_01...
3. Terrain model naming: area name_dx_number; such as: SH01_01_dx_01……
4. Terrain map naming: model name_number; such as: SH01_01_dx_01_01...
5. Hollow texture: add "_al" suffix
6. The glass that needs special effects should be added with "_bl" suffix; (the ones that need special effects should be baked with a single object)
Chapter 7, Create each data path
1. Aerial photo storage path
2. MAX files exported from CAD in each area
3. Photo information
4. Public texture library information
5. All information provided by the customer
Chapter VIII, Special Production Requirements
1. Walls, guardrails, canopies, carports, etc. should be made according to the actual situation.
2. When the photos do not match the drawings, the actual photos shall prevail.
3. The shops along the street should be consistent with the actual situation as much as possible.
4. When estimating the size, try to use the reference objects in the photo, such as people, cars, trees, etc.
5. Except for key buildings, the model should be simplified as much as possible, and the textures should be refined. If the structure can be expressed with textures, it should be represented with textures as much as possible.
6. The types and colors of greening should be as consistent as possible.
7. The structure on the top of the building and the ancillary facilities on the top should be made according to the actual situation as much as possible.
8. When mapping the building, the height of the parapet wall should be reserved at the top to avoid windows reaching the top of the building.
9. The building should have an entrance.
10. The terrain and greenery should be abundant.
11. Newsstands, bus stops, substation boxes, chimneys, signal towers, etc. should be made simply to enrich the scene.
12. The UV size of all textures should be accurate to avoid distortion.