What Is 3D Phase Measurement in Video Borescopes?

What Happens During a 3DPM Capture?

A 3DPM capture records a sequence of frames. The system records white-light images that help track the camera's position relative to the target. It also fires groups of LEDs in sequence to project phase-shifted fringe patterns. Calibration data connects the observed pattern displacement to the known geometry of the tip and camera.

1. The tip illuminates the scene. White-light frames establish the visible surface and help the system detect movement during acquisition.
2. The projection LEDs fire in sequence. Each exposure places a shifted line pattern across the same surface.
3. The surface changes the pattern. Peaks, depressions, curves, edges, and gaps displace or interrupt the projected lines.
4. The processor combines the captures. Phase-shift analysis and tip calibration convert the optical response into surface coordinates.
5. The instrument builds the point cloud. The saved measurement image is linked to a rotatable model used for cursor placement and dimensional calculations.

In the demonstrated Mentor Visual iQ workflow, this sequence takes about two seconds. The projected patterns are not normally shown to the inspector during capture. The visible result is the inspection image and its calculated 3D surface.

Why the Probe Must Stay Still

The processor assumes that every white-light and fringe-pattern exposure describes the same camera position and target geometry. Movement during the sequence can misalign the frames. The resulting point cloud may contain ripples, doubled edges, spikes, disconnected patches, or noise that does not exist on the component.

Hand-held stability may be adequate in some access conditions, but a probe suspended in free space can continue to move even when the operator feels steady. Contact with a vibrating component can cause the same problem. For sensitive measurements, brace the insertion tube or use a probe holder, gripper, or access-port fixture. Keep the component stationary as well.

Stillness during acquisition protects the surface calculation. A perfectly positioned cursor cannot repair data corrupted during capture. When the point cloud does not resemble the component, recapture the scene.

Measurement on Demand: The Practical Difference

A compatible 3DPM tip can provide the viewing angle and depth of field needed for inspection, then capture measurement data when the inspector finds an indication. The operator does not need to withdraw the probe, exchange the viewing optic for a stereo measurement tip, navigate back through the access route, and relocate the same feature.

This matters inside engines and other complex assets where the probe may pass through several bends before reaching the target. Returning to the same location can change the attack angle, working distance, lighting, or component position. Keeping the same tip preserves the inspection context and shortens the path from detection to measurement.

Measurement on demand does not make every live image measurable. The operator still needs a stable capture, sufficient structured-light coverage, a suitable target distance, and enough valid surface data around both the indication and its reference geometry.

The Point Cloud Is the Measurement Audit

The number on the screen is the end of a geometric calculation. The point cloud shows the surface that produced that number. Inspectors can rotate it, view it edge-on, change the depth-map display, and select cursors directly in three-dimensional space.

Start with the full point cloud. Its job is orientation: does the calculated surface look like the component, and is the tip pointed where the white-light image suggests? Look for unexpected waves, spikes, holes, detached islands, or surfaces bridged across a physical gap.

Then open the measurement point cloud. This view isolates the active measurement and the nearby surface. For measurements that use a reference plane, its depth map colors the perpendicular distance from that plane. That makes a shallow pit, raised weld, tilted plane, or noisy extreme easier to identify.

A cursor can be precise and still be wrong

One training example measured blade-tip clearance from a cursor that appeared reasonable in the camera image. Rotating the point cloud showed that a reference cursor sat above the shroud instead of on it. Moving the cursor onto the shroud changed the displayed result from about 0.042 in. to about 0.062 in.

The example is useful because both numbers looked believable. The error came from the reference geometry, not from the number of decimal places. For clearance, depth, and plane-based measurements, view the plane edge-on and confirm that every reference cursor touches the intended surface.

MTD, Signal Strength, and the Measurement Envelope

MTD means maximum target distance. For an active measurement, it identifies the distance from the tip to the farthest cursor point used in that measurement. MTD is a setup indicator and does not specify accuracy.

Distance affects how much usable information the system receives. A small defect occupies fewer pixels as the probe moves away. The projected pattern also returns less useful spatial detail. Noise may then become similar in size to the feature being measured. The instrument can display a result even when the captured surface is not good enough for the decision.

The live signal-strength range guide provides another distance cue with a 3DPM tip attached. More bars generally indicate a stronger return for the scan. During measurement, an orange outline around the result or MTD value warns that the measurement may be too small for the current distance. Move closer or select a larger measurement region, then recapture and inspect the new point cloud.

For small depth measurements below 0.010 in., current Waygate guidance says close placement can matter more than a perfectly sharp white-light image. A slightly out-of-focus 3DPM image may still produce better depth data than a sharp image captured too far away. This does not apply to 3D Stereo, which needs a focused image for feature matching.

Choosing a 3DPM Tip

Choose the viewing direction first. The access port and target position determine whether the camera must look forward or to the side. Then match the optical range to the feature size and available standoff distance. Published depth-of-field values are selection guidance; usable measurement range also depends on surface finish, required accuracy, measurement type, and reflection.

The green side-view design extends measurement range through wider spacing between its projection sources, brighter optics, and larger LEDs. That capability comes with a physical tradeoff: the tip is longer, so it may be harder to steer through tight access or around nearby geometry. The orange forward-view tip makes the opposite trade, favoring close focus and small-feature work over long-range brightness.

Pattern direction matters on narrow targets

The long dimension of a narrow surface should cross the projected pattern lines rather than run parallel to them. Black, orange, yellow, and green tips project horizontal lines in the displayed image, so a narrow target should appear vertically. Blue and red side-view tips project vertical lines, so the target should appear horizontally.

This orientation places more pattern transitions across the usable surface. If the target cannot be rotated, change the probe roll or choose another compatible viewing direction.

How to Read 3DPM Masks and Warnings

Yellow data is not the same as red data. Yellow warns about potential quality loss; red means no calculated surface coordinate is available. Data close to a red boundary deserves extra scrutiny because noise can affect the apparent edge. A Measurement Plane can provide projected reference geometry for certain missing-edge tasks, but it does not create measured surface data inside the red region.

3DPM Measurement Tools That Need More Than Cursor Placement

Length, Point to Line, Depth, Area, and Multi-Segment define familiar dimensions. The tools below add surface searches, projected geometry, or automated feature mapping. They can reduce repetitive cursor work, but the inspector remains responsible for validating the result.

Depth Assist

A Depth measurement uses three cursors to define a reference plane and a fourth cursor to report perpendicular height or depth. Depth Assist searches the nearby surface and proposes the deepest point, highest point, or a point on a blade tip. It saves time locating an extreme, but the proposed cursor must still land on real geometry rather than a noise spike.

Area Depth Profile

Area Depth Profile sweeps many profile slices across a region defined by three cursors and returns the slice containing the highest or lowest point. It fits corrosion fields, erosion, impact damage, weld height, and wear grooves where one manually placed profile could miss the worst location.

This tool can also select a noise peak. For a small indication, move as close as access permits, use an off-perpendicular view, and inspect whether the feature rises clearly above local point-cloud noise. On a curved parent surface, place the two reference profile lines so they follow the surface contour; do not send the profile slices along the direction of curvature.

Measurement Plane

A Measurement Plane is an aid used with another measurement type. Three cursors establish a mathematical plane on valid reference data. Length, Point to Line, Multi-Segment, or Area cursors can then be projected onto that plane across a missing edge or noisy region.

The plane is always mathematically flat, even when the selected component surface is curved. That makes reference-cursor placement critical. Use the green mask to maximize agreement with the surviving local surface, rotate the point cloud, and view the plane edge-on before measuring missing material.

Blade Tip Clearance

Blade Tip Clearance identifies the blade and liner, maps the visible blade edge, and reports minimum, maximum, and average clearance across the accepted region. A long-range green side-view 3DPM tip can capture near and far surface data across a wider scene, which helps include the blade edge and liner in one point cloud.

Review the liner plane, the mapped blade-edge line, excluded end regions, and every advisory message. Honeycomb liners, shrouded tips, irregular edges, glare, and missing 3D data can limit the automated result.

Radius Gauge

Radius Gauge places a 3D circle of known radius or diameter on the captured surface or on a Measurement Plane. It provides a visual size comparison for rounded damage or component features. The circle follows the surface perspective in the point cloud, so it is more informative than laying a flat circle over a 2D image. It remains a gauge comparison rather than an automatic defect classification.

Why Off-Perpendicular Views Often Produce Better 3DPM Data

A straight-on view may send mirror-like reflections from a shiny surface back into the camera. Those reflections can wash out the projected pattern and create yellow or red data. Tilting the view redirects the specular reflection away from the lens while preserving enough pattern coverage for the surface calculation.

This guidance is especially important for small depth and Area Depth Profile measurements. The target and its reference surface must remain visible, and the angle cannot be so steep that the feature hides behind an edge or falls into projection shadow. Use the point cloud and masks to judge the result instead of assuming one angle is always best.

A Practical 3DPM Failure and Recapture Example

Consider a shallow dent on a curved blade surface. In a poor capture, the tip is farther away than necessary and almost perpendicular to a shiny target. The point cloud shows bumps across the parent material, the dent shape is not distinct, and the automated profile selects a positive noise peak even though the visible feature is a depression.

The corrective capture uses a close-focus forward-view tip, moves nearer to the target, and approaches from an oblique angle. The reference profile lines follow the blade curvature. In the new point cloud, the parent surface is smoother, the depression has the expected shape, and the reported result is negative relative to the reference surface.

A measurement tool can return a number from poor data. Accept the result only when the sign, feature shape, mask behavior, cursor geometry, and surrounding noise all agree.

3D Phase Measurement vs 3D Stereo

Both methods create a point cloud, but this cluster concerns the structured-light workflow. The comparison below is included only to identify conditions where a different capture method may be more suitable.

Choose between the methods by testing the proposed probe, tip, measurement type, target distance, and surface on representative known samples. One universal accuracy claim cannot describe every application.

Field Protocol for a Defensible 3DPM Result

1. Define the required dimension. Identify the maintenance limit and whether it depends on length, perpendicular depth, area, profile, missing geometry, or clearance.
2. Use a qualified procedure. Confirm operator qualification, approved technique, units, and acceptance criteria.
3. Inspect and verify the system. Clean the probe and tip optics, secure the tip, and complete the prescribed checks with the applicable traceable verification block.
4. Select the tip for access and scale. Match viewing direction, near and far optical range, feature size, and projected-pattern orientation.
5. Move close enough. Fill the image with the feature and a usable reference surface. Watch the signal guide and MTD.
6. Control the angle. Redirect glare and avoid projection shadow while keeping the entire measurement geometry visible.
7. Stabilize the probe and component. Hold both still through the full white-light and fringe-pattern sequence.
8. Read the data masks. Avoid yellow data for sensitive depth work and do not place direct measurements in red data.
9. Rotate the point cloud. Confirm the surface shape, reference plane, cursor contact, and feature sign.
10. Use the depth map. Make sure a small feature is distinct from local 3D noise.
11. Audit automated geometry. Verify Depth Assist, Area Depth Profile, Blade Tip Clearance, and other proposed results.
12. Recapture weak data. Post-processing and cursor movement cannot recover missing or motion-corrupted surface information.

Saving and Re-Measuring 3DPM Data

A saved 3DPM image can contain more than the displayed measurement. In ZMap format, the file stores computed 3D surface data for later re-measurement and produces a smaller file. PMap stores the original projected-pattern images so the software can process the 3D data again; it is generally reserved for development and troubleshooting.

Supported on-device or desktop workflows can reopen the measurement, add or move cursors, clear results, rotate the point cloud, and export point-cloud data. Preserve the original file when later review matters. A flattened screenshot records the visible result but does not retain the same measurement data.

Re-measurement can correct cursor placement. It cannot correct a capture made from too far away, through severe glare, or while the probe moved. Those conditions require a new field capture.

Choosing a Video Borescope for 3DPM

The Mentor Visual iQ+ video borescope is the primary Waygate platform to evaluate when the inspection requires 3D Phase Measurement, interactive point-cloud review, advanced measurement tools, and compatible forward-view or side-view tips. Confirm the exact probe, tip, software, and license configuration before purchase or rental.

The Mentor Flex+ VideoProbe supports different inspection and measurement configurations. Choose between systems using the access diameter, working length, viewing direction, target distance, surface condition, measurement type, and reporting workflow rather than the instrument name alone.