Mesh - PIX4Dmatic

Mesh

The following processing options can be adjusted when enabling the mesh generation:

• Input (Optional)
• Template
• Texture size
• Deghosting
• Decimation
• Plane-aware
• Interior improvement
• Sky mask
• Smoothing
• Exports

Information: The Mesh can be visualized directly in PIX4Dmatic, in the 3D view. To access the 3D view:

• In the menu bar, click View > Switch to 3D, or
• Click the 3D button on the screen , or
• Use shortcut 3.

It can also be uploaded to PIX4Dcloud, for visualization. For more: How to upload or replace results to PIX4Dcloud.

Input (Optional)

It allows selecting the input point cloud for the Mesh generation. The following options are available:

• Dense point cloud (default): The point cloud generated from images during the Densify step.
• Depth point cloud: The point cloud generated from LiDAR depth maps.
• Depth & dense fusion: The point cloud that present a fusion of the dense and depth point cloud.

Template

This option enables distinguished default parameters for the mesh generation algorithms used for the different types of datasets imported into the software. The following templates are available for the Mesh generation:

• Aerial (default): Ideal for scenes with a larger extent. Typically drone flight size projects that contain oblique or nadir data.
• PIX4Dcatch: For projects with limited extent. Optimized for hand-held captured data with PIX4DCatch.
• Thin structures: For projects that capture thin structures, i.e., cables, powerline tower structures, and antennas.

Texture size

Texture Size (1024x1024 - 32768x32768 pixels, default 8192x8192 pixels): Parameter used to define the resolution of the texture of the Mesh.

Deghosting

This option enables different parameters for the mesh generation algorithms used for the different types of datasets to improve the mesh results. It can remove objects and can be beneficial in case of highly complex geometries. The following deghosting options are available for the Mesh generation:

• Weak (default): Ideal for soft outlier detection. Recommended in general cases. It may cause artifacts though, with moving objects or thin structures such as cables, powerline tower structures, and antennas.
• Strong: Aggressive outlier detection. May give better results when the geometry is highly complex (e.g. telecom towers) or when a lot of objects are moving in the scene (e.g. pedestrian street). The downside of the strong setting is that it could cause desaturation of color and loss of sharpness.

Decimation

Decimation (1.000.000 default): The maximum number of triangles in the final Mesh. The number will depend on the geometry and the size of the project.

The final number of Triangles created during the Mesh can be found:

• In the project log files:

[Decimate mesh geometry](Info) Triangle count: ######

• In the Status center, under the Decimate mesh geometry step:
  

Plane-aware

This option, when selected, enables the use of planes and polygons to improve the mesh quality. It is possible to select or deselect the desired layers, that have been created in the project. This option is only enabled when at least one polygon/plane is created and associated with a layer. 

PIX4Dmatic allows for the manual creation of Planes/Polygons. To create these features, ensure that a point cloud is visible, click on Tools, and select Polygon. Alternatively, the keyboard shortcut P can activate the tool. Once activated, vertices will snap to the point cloud, MTPs, or ITPs. Left-click to add vertices. Right-click to add the final vertex and complete the Plane/Polygon.

After creating the Polygon, the following options are available by right-clicking: 

• Invert selection
• Delete polygon
• Move to layer
• Flip polygon normals
  • The Normals is a line that is perpendicular to the plane. It indicates the direction or what would be considered the plane's outer surface. The Plane normals can be turned on by going to the 3D viewer settings and toggling on the Normals. Magenta arrows display the Plane normals, as viewed in the image below. Correctly setting the direction of the Plane normals provides for a better mesh reconstruction and viewing experience. Ensuring that the normals of a plane point to the direction of the cameras used to capture that surface is imperative. To flip the Plane normals, right-click on the plane and select Flip normal.
    
• Set polygon to planar
• Set polygon to non-planar
• Create section from polygon

Interior improvement

When creating and editing Planes for interior scenes, it is recommended to use the Backface culling feature in the Settings. When enabled, this feature allows for backward transparency for the Planes. The Plane will be opaque when viewed from the front. However, it will be transparent when viewed from behind. This allows for an obstructed view of interior scenes.

Sky mask

Sky mask utilizes the generated mask during the Dense point cloud step to improve the mesh quality. It is enabled by default when the Sky filter option is enabled while running the Dense point cloud step.

Smoothing

This option, when enabled, affects the mesh geometry and applies a smoothing effect to the generated mesh.

Exports

From the Exports section, the following can be exported after processing the Mesh step:

• Point cloud from mesh .laz
• Mesh

Pointcloud from mesh .laz

PIX4Dmatic allows the generation and export of point clouds from the mesh. The default Density (pts/m³) or a customized one can be selected while exporting the new point cloud from the mesh. The expected point cloud size and the total number of points are also displayed while exporting the point clouds. This way, a point cloud is generated even for areas that are not directly reconstructed and holes no longer exist in the reconstructed point cloud. The point cloud generated from the mesh is in .laz format.

Note: This point cloud is expected to have a much bigger size than the point cloud files that are generated during the Dense point cloud step.

Mesh

Access: Once processed, the Mesh can be exported from the file menu ( File>Export mesh...) or the processing panel ( Exports>Mesh).

The following formats are available when exporting the Mesh:

• obj (default): PIX4Dmatic exports a Mesh obj that is not georeferenced. It has coordinates in a local coordinate system (Export CRS: Default) centered around the project. With some external viewers, it is possible to add an offset.xyz file to correctly position the Mesh. Once completed, the Mesh will have the same precision as the mesh viewed in PIX4Dmatic. The project_name_offset.xyz file contains the offset of the project and is stored in the folder with the .obj file. The export CRS can also be selected as the Project CRS. 
  
  
• .ply: When this format is chosen, the texture coordinates can be picked between per face and per vertex. Meshes with per vertex coordinates can be imported in Blender and Meshlab. Meshes exported with per face coordinates can be imported into Meshlab. 
• Cesium 3D Tiles: The Cesium 3D Tiles are georeferenced. This format allows the Mesh to be easily shared and displayed across many third-party software and 3D platforms. The primary purpose of 3D Tiles is to improve the streaming and rendering performance of massive heterogeneous datasets. The foundation of 3D Tiles is a spatial data structure that enables Hierarchical Level of Detail (HLOD). When selecting and exporting the Cesium 3D Tiles a .json file and various .b3dm files are generated inside the folder project_name-cesium_mesh.
• slpk: A Scene Layer Package (SLPK) file is an openly published file format for 3D geospatial data, designed as a package for storage or exchange that captures all resources for a "scene layer" structured according to the Indexed 3D Scene Layer (I3S) specification. Mesh (LOD) can be exported as .slpk for ESRI compatibility. The SLPK Mesh file is geo-referenced, and the exported multi-LOD mesh in .slpk format is named project_name-mesh.slpk.