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What fSpy does
fSpy is a standalone, open-source, cross-platform application for matching a 3D camera to a still photograph. Its source code is licensed under the GPL, and the project offers executable downloads. fSpy calculates camera parameters from image measurements; it does not create the photographed scene’s geometry for you.
You can use the resulting camera parameters in other 3D applications that allow camera settings to be entered. Without a dedicated importer, that handoff may mean manually copying the values.
How fSpy estimates a camera
The basic setup uses a real-world rectangular feature—such as a wall, floor, or building face—with edges known to run in two perpendicular directions. You mark the rectangle’s corners so fSpy can derive the corresponding vanishing points. A 3D origin control supplies a reference for the camera’s position. Together, the two vanishing directions and the origin form the five-point setup described in the fSpy tutorial.
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Vanishing directions and the origin
The vanishing points help determine focal length and camera orientation. The origin control defines the camera’s position relative to the scene axes. As you adjust controls, fSpy updates the calculated parameters. Shift-drag can be used for finer control.
Use the 3D guides to check whether the axes implied by the solve follow image features that should be straight and aligned. If the rectangle control does not fit the photograph, the tutorial describes moving the controls for each vanishing point independently instead.
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Axis assignment
fSpy color-codes the coordinate axes red, green, and blue and lets you assign axes to vanishing-point directions. Check this mapping before importing: the destination application may use a different convention for which direction is “up.” An axis mismatch can make an otherwise useful camera appear oriented incorrectly in the 3D scene.
Set scene scale and check the principal point
Establish real-world scale
A perspective match does not automatically tell you how large the scene is in real units. fSpy’s camera-to-origin distance starts at a fixed reasonable value; to set scale, provide a known dimension in the image and align the reference-distance handles to it. The tutorial demonstrates the process with a tile known to be 20 cm wide. That is an example measurement, not a required tile size.
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Use a dimension you can measure reliably and identify clearly in the photograph. Any uncertainty in that reference carries into the scene scale.
Adjust the principal point when needed
The principal point is where the ray through the center of the lens meets the sensor or film. It commonly lies at the image midpoint, but asymmetric cropping can shift that relationship. If you know the principal point, the tutorial says you can place it manually; in supported configurations, fSpy can infer it from a third perpendicular vanishing point.
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What if the image has only one vanishing direction?
A one-vanishing-point calibration is possible, but that visible direction by itself does not fully determine the camera. The tutorial says this setup requires additional information from the user: the camera’s focal length and the direction between the first and second vanishing points. If you do not know or cannot reasonably estimate those inputs, the image may not provide enough information for a dependable solve.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Import an fSpy project into Blender
The Blender importer is a separate add-on from the fSpy application. The importer repository’s published instructions describe this workflow:
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- Download the importer ZIP from the fSpy Blender importer repository.
- In Blender, open Preferences and install the add-on from the downloaded ZIP, then enable it.
- Use Blender’s Import menu to select the fSpy project file.
- Review the imported camera, named after the project file. The importer offers options to update a matching existing camera and to bring in the project image as the camera background.
The repository states that importer version 1.0.3 is compatible with Blender 2.80 and up; for older Blender versions, it directs users to version 1.0.2. That published compatibility floor does not by itself confirm that version 1.0.3 has been tested with every later Blender release, including Blender 4.2. For a particular Blender version, check the repository’s current release information and test the exact app and add-on versions you plan to use.
Where a camera match can be inaccurate
- Lens distortion: Curved distortion can make image lines depart from the straight perspective geometry the solve assumes. The tutorial identifies lens distortion as a possible source of error.
- Uncertain right angles: A feature that only appears to form exact right angles can lead to incorrect vanishing directions and a weaker solve.
- Weak or ambiguous perspective cues: The method relies on interpretable vanishing directions and correct assumptions about which scene directions are perpendicular. Sparse images may require additional focal-length, direction, principal-point, or scale information.
- Scale and crop assumptions: A scale based on an inaccurately measured object will be inaccurate, while asymmetric cropping can make an assumed image-center principal point unsuitable.
Check the 3D guides against several image features rather than relying on one corner or line. In one undated tutorial example, fSpy estimates a 26 mm focal length where the example camera/lens value is 24 mm. This illustrates a result from that project only; it is not a general accuracy statistic or benchmark.
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