Model preparation Guide

About

Mentioned criteria

1. Usable amount of vertexes (Depends on the use case mentioned below)

2. No inverted polygon faces (Depends on the use case mentioned below)

3. No duplicated vertexes

4. Use instanced assets instead of unique ones

5. No empty objects, parents, bones, or unnecessary stuff

6. The maximum object number in a single model should not be higher than 6K (We can go higher but it can make the model unusable for us)

7. Easy and understandable named materials, textures

8. Keep the maximum number of materials/textures per single object as low as possible (Depending on the use case)

9. Correctly created and assigned UVs

10. Small final file size (On the automatic Twinzo platform system file size limit is 100MB)

11. Supported formats

Criteria divided by use case

The single model used in the app

Non Scanned or Lidar based:

If we want to visualize only a single object in the app, usually criteria tolerance are much higher. For example, this single machine has over 500K vertices. Which is the top limit in terms of vertices amount. Everything higher will be most likely not usable. Also well amount of materials/textures on a single object can be higher.

Open

Non Scanned based model

Scanned or Lidar based:

For scanned or lidar-based meshes (In the case of lidar-point cloud converted to mesh), criteria are not as strict as for their counterparts. Usually, if your model has many vertices (under 2M) and the number of materials with textures is not exceedingly high (under 100), then your model should be fine (depending on your smartphone performance).

Multiple assets used in the app

If we want to visualize assets in the app, for example, something that is part of a factory/office and appears multiple times, criteria tolerance is much lower. For example, palette boxes, press machines, cranes, furniture, etc...

• 2K or less vertices - simple material or textures with/without UVs,

• 3K/4K or fewer vertices - important to visualize the model in more detail and it doesn’t appear numerous times,

• Models that are visualized 5, or 10 times in one scene without any additional used assets can have a higher amount of vertices with higher texture resolution and more UVs. For example parts of cities or factory/office complexes.

Visualizing multi-floor building

If you want to visualize a building that has multiple floor levels, it's important to try to separate each floor into individual parts with specific hierarchies so, in the end, we can switch between them.

We prepared a full guide on how to prepare the model if you want to do it yourself: https://twinzo.atlassian.net/l/cp/g9PJ2SxQ

Visualizing BIM models

However, we can process BIM models outside the automatic twinzo platform agent. You can learn more about it here → https://twinzo.atlassian.net/wiki/x/BYBFFg

Common model errors to look out for

These include the most common errors present in most models. These should be avoided and fixed.

1. Scaling and Units

• The model should use a real-life scale in meters (1 Editor Unit = 1 meter). Models outside of these ranges, or in different units, can cause precision issues.

• The main building volume should be roughly centered around the world origin (X = 0, Y = 0, Z = 0).

Open

2. Inverted polygon faces

The red inside faces visualize which parts of the mesh are going to be invisible (backface culling) when rendering in the application.

3. One-sided geometry

A single face will have its back side invisible (culled). Walls should be solid and have volume.

4. Vertex Normals

Vertex normals are vectors that define which way a vertex is pointing.

The purple lines on the image below are visualizing the normals of each vertex of the dome. (Red surfaces visualize inside faces that are going to be culled)

The Vertex normals on this house have been modified. Notice how the lighting looks wrong because the Vertex normals are not consistent with the faces.

5. Overlapping and Duplicated geometry

This step is very important. Overlapping geometry causes flickering (Z-fighting), and lighting errors, and such duplication wastes resources.

6. Cleaning up bottom faces

Cleaning up bottom faces and parts of the mesh that are never going to be seen saves texture space and computational resources. Downwards-facing geometry is never going to be seen in the twinzo application, therefore it only wastes memory and resources and should be removed from the model.

In the clip below:

1. Geometry is selected based on the normal facing direction

2. The selected downwards-oriented faces are deleted. (Red faces visualize inside faces that are going to be culled)

7. Object Instancing

This one is also very important to follow.

All 10 of the blue objects use the same mesh. They are all individual separate objects, but all of them use the same mesh.

Modifying the mesh of one instance reflects on all of the instances using that mesh.

In the clip below only the rightmost selected object is being modified, all other objects to the left of it reflect the changes because they are using the same mesh. They are instances.

All repeating or duplicated objects should use instances instead of “deep” copies that also use a duplicated mesh.

8. Object number

It is recommended to keep the number of individual objects under 6000 for a single scene. Fewer objects mean better computational performance for mobile devices and also it will reduce processing time. If your 3D model has many more objects, you can partially overcome this issue by using instances of “meshes with shared geometry” or merging objects that are divided into multiple separate pieces.

9. Materials

Objects should generally have the least possible amount of unique material slots assigned/used. E.g. There’s no need to have 5 different metal material types assigned to one object unless they’re vastly different in appearance.

The number of unique materials in the final exported file should be reduced to the minimum amount possible.

This means:

• No material duplicates (Metal Chrome, Metal Chrome.001, Metal Chrome.002, Metal Chrome.003, etc...)

• No redundant materials with very slight changes in color or other properties.

• All materials should be named properly, clearly, and descriptively. E.g. Wall Yellow, Metal Dark Rough, Glass, Plastic Orange Shiny, Carpet Brown, etc...

• If you are using PBR materials with various texture images and want to upload a model through the automatic twinzo platform agent, please visit this tutorial: How to embedd Textures into single file

10. Supported file formats

• Through automatic Twinzo platform - .fbx, .obj, and .mtl,

• The preferred file format is a binary .fbx,

• Possible to work with outside automatic twinzo platform agents - .fbx, .obj, .mtl, .stl, .stp, .ifc, .dae (limited) and glTF 2.0,

• Possible to export outside the automatic twinzo platform agent - .fbx, .obj, .mtl, .stp, .dae (limited), and glTF 2.0,

• The model file should have ~100Mb.

Every format has its limitations. Generally .fbx, glTF 2.0 or .obj are most suitable for us. Other formats like .stl or various .cad models cause different problems, like missing materials, unable to open, unable to properly convert, huge sizes, and no instances.

What software are we using?

• Unity 2022+

• Blender 3.6+

• Meshlab 2021.05+

• AutoCAD 2023

• CAD Assistant