From Photos to 3D Spatial Data
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This guide will cover using Agisoft Metashape to produce a point cloud and/or mesh from a set of photos.
Agisoft Metashape Professional v.1.6.2 was used in this article.
When first entering the program, it helps to recognise the layout of the software. In Figure 1, the following highlighted sections are:
Red: Workspace and reference panel. Here, a list of your chunks, images and points as well as markers and reference points are located.
Blue: The model space. This is where you interact with the photogrammetry model, a gumball is always present to give you orientation along with the axes gizmo in the bottom-right. There is also a Photos tab that will appear if one tries to edit a photograph
Yellow: Photos, console and job timeline. Photos timeline is the important one here; they show the status of each image (aligned, marked) and allow one to add markers in each image. The console tab is used for debugging and the job tab is not used.
Orange: Quick access toolbar. Various tools, and options are located here.
Command
Function
Right Mouse Button (Hold)
Pan
Left Mouse Button (Hold)
Rotates around the gumball
Ctrl + Scroll Wheel
Change perspective angle
Metashape is a fairly straightforward software to use, the majority of the workflow is covered by going down the [Workflow] menu on the top.
Ensure the GPU is enabled, this will speed up processing times considerably.
Under [Tools > Preferences > GPU], ensure the GPU device is enabled. On University systems, these are GeForce RTX 2080 and GeForce GTX 1080.
The first step is to add the photos you have taken to the software.
Right-Click in the Workspace, and add a [New Chunk]. Metashape processes a set of images as a 'chunk'; think of it as a layer in Photoshop or other software. Figure 2, 3 & 4 shows how chunks and photos are added.
TIP: You can select and use/view any chunk by double-clicking it.
Use [Workflow > Add Photos] to open up your system's File Explorer, navigate to your photos and select all of them.
Once the photos are added, they will appear in the Photos panel and will be listed in the chunk in the Workspace on the left (Figure 5).
When your photos have all been inserted into Metashape, the next step is to instruct Metashape to align the photos.
Metashape uses a process where it will generate Feature Points called tie-points through triangulation of the photos. This process can vary in processing time depending on the quality selected.
Use [Workflow > Align Photos] to begin the alignment process.
In general, 'Medium' settings are a good compromise between processing time and output quality. The other settings can be left as is as well. If you require higher quality you can adjust it accordingly but be wary of time.
When completed, one can see the position of the image's capture location mapped out around the tie-points. These are called cameras by Metashape.
If your photos do not align properly at this stage, it would be wise to reconsider your matrix, or refer to the Advanced Techniques: Manual Markers to assist in the alignment process.
It is useful to know how to show and hide elements in the model space as well as shortcut controls. Open [Model>Show/Hide Items] to view a list of interface elements.
The important ones to keep note are:
[Show Cameras] controls the visibility of the cameras that surround the model.
[Show Thumbnails] controls the visibility of the cameras thumbnail image.
[Show Markers] controls the visibility of the markers in the model space.
[Show Trackball] controls the visibility of the trackball at the centre of the model space. Note that the trackball is not visible when other tools such as the Selection tool is used.
[Show Grid] controls the visibility of the grid.
Some of these visibility controls are also located on the toolbar.
The process of aligning photos tend to generate some tie-points that are floating far away and surrounding the model. Cleaning this up will greatly assist the legibility of the object in further processes.
In the toolbar, look for the Selection tool (see image below). The drop down menu shows several selection options such as [Rectangular], [Circular] and [Free-Form]; choose whichever is applicable.
Then, one can select the stray/unwanted tie-points in the model space by marquee selecting (left click and drag) these points. Simply hit the Delete on the keyboard to remove these points.
Dense clouds are essentially a high count (and therefore high detail) point cloud that is generated by interpolating and point matching the existing tie-points and data from the images.
It allows the generation of meshes and detail reproduction of the object. This part of the process does take a lot of time. Do plan ahead.
To do this, go to [Workflow > Build Dense Cloud].
In the Build Dense Cloud dialogue box, choose your quality settings. It is recommended to set 'Medium' quality for a balance of processing time and quality. Stick to the default settings for the rest.
Once the dense cloud has been built, it does not appear on the screen immediately. You can control the visibility of the dense cloud through the toolbar. Locate the Dense Cloud icon (see image below) and click on it to make the dense cloud visible.
Agisoft Metashape can produce a mesh from the dense cloud that can be exported out to other softwares for fabrication purposes.
To do this, go to [Workflow > Build Mesh].
When the Build Mesh dialogue box appears, select the mesh quality that you desire.
All Export options are found under [File > Export]
Agisoft Metashape can export to a variety of standard file types.
Point clouds contain exact points and information pertaining to each point, such as colour and the normal plane of the point.
In the Export Options, you can choose which of these qualities to save. Usually you would want the Source Data to be the [Dense Cloud] for a complete point cloud.
Do not convert colour to 8-bit.
TIP: .PLY, .XYZ and .E57 are common Point Cloud filetypes. Use .PLY if you intend to use this object with Rhinoceros 3D.
Meshes are exported in a similar way.
TIP: .OBJ and .PLY are common Mesh filetypes.
With a point cloud/mesh generated, you can now take measurements.
Show Images allows you to view snapped images to double-check the alignment.
