Surface Topography Measurement 

using GelSight Elastomeric Sensor

Marcus A. Brubaker (marcus@cadreresearchlabs.com)

Cadre Research Labs

With:

Ryan H. Lilien

Micah K. Johnson

Todd Weller (Oakland Police Dept, Criminalistics Lab)

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Marcus A Brubaker (Marcus@CadreResearchLabs.com)

What is GelSight?

Cookie

Clear Elastomer

Paint

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Marcus A Brubaker (Marcus@CadreResearchLabs.com)

What is GelSight?

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What is GelSight?

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Why is it difficult to measure surface geometry?

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Emery board

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Hard elastomer

Tire tread

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Soft elastomer

Soap bubbles Bubbles touching GelSight

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Oregano leaf

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Oregano leaf: close-up

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Oregano leaf: close-up

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Skin topography

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How does GelSight work?

• The gel is visco-elastic.

• Under pressure it flows, filling the holes.

• The specimen is “coated” with a layer of thin elastic paint.

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Peacock feather

Direct view GelSight view

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Glue droplets on Post-it note

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Elements

reflected 

Lambertian 

Model 

eye

Measuring 3D shape with GelSight

Classic computer vision problem: “shape-from-shading”

Diffuse (Lambertian) shading

If there are multiple images with different light sources

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Setup

Camera

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Dime under sensor 3D Rendering Close up

Surface Topography Measurement

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GelSight measurement of cartridge cases

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GelSight measurement of cartridge cases

We measured the breech face impressions on six fired cartridge cases from 

three consecutively manufactured firearms

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GelSight measurement of cartridge cases

Confidential - Do Not Distribute

Confidential - D

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Matching of breech-face impressions

Matching GelSight measurements of breech-face impressions

• Select feature points on the 3D surface which are identifiable and invariant 

to moderate amounts of scaling and changes in impression depth

• Match impressions by matching these feature points

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Matching of breech-face impressions

Correspondence of features (match)

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Matching of breech-face impressions

Correspondence of features (non-match)

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Matching of breech-face impressions

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Marcus A Brubaker (Marcus@CadreResearchLabs.com)

Conclusions

GelSight sensor provides a new way of looking at surfaces

• Non-destructively painting the surface removes material effects

Accurate 3D reconstruction of surface topography

• 3D surface measurement removes influence of lighting

A novel approach for matching breech face impressions with 3D geometry

• Matching feature points provides a high level of distinguishability

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Validation

Lenticular sheet

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Rubert specimens

#530: Period 100μm, Height 3μm

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Rubert specimens

#525: Period 135μm, Height 19μm

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