Recommended external pattern projector for D405 (visible, 7 cm working distance)
Hello,
I'm planning to use D405 for close-range depth measurement at a fixed working distance of about 7 cm. The surfaces are soft, translucent, organic material with moist, glossy and matte regions, and they show significant subsurface scattering. They are often low-texture, so I want to add an external random-dot projector to improve stereo matching.
My constraints:
- Wavelength: since the D405 senses visible light, I'm planning a green (~520 nm) direct-diode laser. I've ruled out red because it penetrates these translucent surfaces and scatters beneath them, which blurs the dots. Blue is also an option, though it may be absorbed more in the darker areas.
- Pattern: pseudo-random dots, ideally 15,000+ dots, sized for the D405's FOV at 7 cm.
- Exposure: pulsed for at most 10 ms per capture, triggered in sync with the camera.
- Safety: IEC 60825-1 Class 1 preferred, since people will be nearby.
My questions:
- Has anyone used a specific external projector with the D405 successfully? I'd appreciate product names or part numbers. I'm currently considering the Osela RPP (custom 520 nm), Lasermate GMS/GMP series, or a Holo/Or random DOE with a single-mode 520 nm diode.
- What dot density or dot size works best with the D405's stereo matcher at close range? Is there a point where too many dots hurt matching?
- Are there recommended depth presets or settings (exposure, gain, post-processing) when using an external visible projector on the D405?
- At 7 cm, will the projector's dots be sharp enough, given that DOE patterns are usually designed for the far field? Has anyone needed a projector focused specifically for such a short distance?
Thank you for any experience or suggestions.
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Hi Venkata Subbarao Thanks very much for your questions.
1. I have previously suggested using a visible dot pattern projector like the one at the link below, though I have not tested it myself. A dot pattern is the ideal type of projection to use with RealSense cameras.
https://github.com/realsenseai/librealsense/issues/13036#issuecomment-2242839115
2. The more dots that are projected into the camera's field of view, the better the depth analysis. The image below is considered to be an ideal dot pattern projection.
3. There are not recommended settings for a visible pattern projection other than that it resembles the ideal image above as closely as possible.
4. RealSense's guide paper (below) for using an external projector with RealSense cameras recommends choosing a projector with a programmable dot density if possible so that the density can be increased or decreased depending on resolution.
https://dev.realsenseai.com/docs/projectors/
Guidance on visible projectors can be found in Section 6 of this guide.
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Hi MartyX Grover, Thanks for the detailed explanation and link.
A general question out of curiosity: the D415/D435 family pairs IR stereo sensors with a separate RGB sensor and a built-in IR dot projector, but the D405 uses its two visible-light sensors for both depth and color and has no projector. Was there a specific technical reason for that choice at close range ?
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The left and right sensors on D405 are IR sensors like the rest of the 400 Series family. D405 does not have a dedicated RGB sensor or an IR projector though. It does not have a projector because the IR sensors have an "IR-Cut" filter attached to them that prevents the camera from seeing near-infrared light frequencies like those used by the projector, only visible light frequencies. The omission of an RGB sensor enables D405 to be a compact size, less wide than D415 / D435.
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