Patent Application
20100292955
The invention generally relates to methods and systems for measuring the microrelief of objects, and is particularly suited for characterizing the periphery of cylindrical objects such as trees, telephone poles, and pipes.
“Bark microrelief” is a term used to refer to the configuration of the bark surface of a tree with respect to the spatial patterning of bark texture (i.e. the surface profile). Bark microrelief is inherently different among tree species and within tree species as a function of age. The variability in bark microrelief of individual trees is of great importance to the ecophysiological functioning of forest ecosystems. In particular, the distribution of corticolous lichens and bryophytes is partly governed by bark texture and bark water storage capacity which, in turn, directly and significantly affects stemflow yield and chemistry. Parmelia sulcata Tayl., for instance, demonstrated a significant association with bark ridges, whereas Physcia grisea Lam. exhibited a significant association with bark furrows. Quantification of bark microrelief is a challenging but important endeavor to better understand the functional ecology of forest ecosystems. This measure may be utilized to examine change in bark microrelief with disease, lichen growth, or diurnal changes due to stem dehydration. Trees infected with beech bark disease, for example, exhibit physical deviations in the bark surface. Recognizing the importance of bark microrelief to the distribution of lichen species, an instrument to quantify bark microrelief was designed in the late 1960's. The instrument designed and described by Yarranton 1967 consisted of a hinged aluminum ring manually screwed into a tree. A total of 180 hand measurements were collected around the circumference of sample tree boles, accounting for a measurement every 2°. Hitherto no instrument existed to characterize the inherent variability of bark microrelief with high spatial resolution.
One aspect of the invention comprises a apparatus for determining microrelief of an object periphery, the apparatus comprising a ring for attachment to the object, the ring defining a path at a fixed distance from a central axis of the object; a carriage adapted to traverse the path defined by the ring; a non-contact measurement system mounted on the carriage; an advancement mechanism configured to incrementally advance the carriage to a plurality of locations along the path; and a processor configured to receive and process an output of the measurement system. The non-contact measurement system comprises a transmitter, such as a laser transmitter, adapted to transmit a beam of radiation toward the periphery of the object, and a detector, such as a CCD camera, adapted to detect at least a portion of the radiation reflected from the object. The processor is configured to process the measurement system output to determine a distance from the object periphery to the detector at each of the plurality of locations of the carriage along the path and to automatically determine the microrelief of the object periphery from the measured distances. The apparatus may be particularly adapted to determine bark microrelief of trees, poles, pipes, or any other types of cylindrical objects. The processor may be configured to provide an output in the form of a pictoral representation of the bark microrelief plotted in polar coordinates using the measured data provided by the measurement system.
The apparatus may further comprise a user interface and a power source connected to the processor. The same power source may also be connected to the measurement system and the advancement mechanism. The angle of incidence between the transmitter and the detector may be adjustable, and may be parallel or perpendicular to the plane of the ring. In one embodiment, the processor is programmed with instructions to cause the apparatus to perform the steps of (a) measuring the distance from the measurement system to the periphery of the object at a first location using the measurement system; (b) recording the distance from the measurement system to the periphery of the object in the processor memory; (c) incrementally advancing the carriage along the ring using the advancement mechanism; (d) repeating steps (a)-(c) until the carriage has fully traversed the ring; and (e) plotting the measured distances from the measurement system to the periphery of the object using polar coordinates to provide a pictoral representation of the bark microrelief.
Another aspect of the invention is a method for determining the microrelief of an object periphery, the method comprising the steps of (a) mounting a ring around the object at a fixed distance from a central axis of the object; (b) mounting on the ring a carriage containing a measurement system; (c) measuring, without contacting the object, a distance from the measurement system to the periphery of the object; (d) recording the distance from the measurement system to the periphery of the object; (e) incrementally advancing the carriage along the ring; and (f) repeating steps (c)-(e) until the carriage has fully traversed the ring. The method may further comprise (g) plotting the measured distances from the measurement system to the periphery of the object using polar coordinates to provide a pictoral representation of the bark microrelief.
Although illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.
The present invention will be further described based on embodiments as examples, but embodiments of this invention are not limited to these examples. Additional embodiments of this invention may include, but are not limited to instruments for the measurement of the microrelief of the periphery of any object, such as, for example, the measurement of corrosion or deterioration of the exterior of a pipe, such as in a pipeline. While ideal for measurement of microrelief of the periphery of cylindrical or substantially cylindrical objects, the instrument described herein is not limited to specific types of measurements, specific objects to be measured, or specific periphery geometries.
The instrument described herein provides a viable alternative for the quantification of microrelief. This instrument may be employed by scientists to better understand plant physiological ecology. As shown in
An exemplary carriage assembly 300 shown in
In one exemplary arrangement, camera 314 is mounted to camera frame 316, as shown in
The camera frame 416 may be mounted on the carriage assembly 400 in a horizontal orientation as shown in
As shown in
The laser emitter and the CCD sensor may be aligned such that the range to the target can be calculated through triangulation of the brightest pixel in the CCD image. The CCD sensor is secured in place by the camera frame 316,416, as shown in
As described above, the laser rangefinder sits on a mobile carriage assembly. The carriage assembly may be aluminum or fiberglass chassis and may have a durable, waterproof plastic housing. The carriage assembly may be powered by, for example, a removable lithium-polymer or similar high density battery attached to the chassis and controlled by an on-board microcontroller. Aluminum “undriven” (non-powered) wheels 342, 442 are pinned such that they ride on the inner diameter of the ring, holding the carriage in alignment as it travels around the tree. The laser emitter and CCD sensor, which together make up the rangefinder hardware, are precisely located on machined features such that they always point at the central axis of the ring.
As shown in
When in use, the entire apparatus may be driven by a controller/processor (not shown), such as a laptop computer, personal digital assistant (PDA), or a dedicated interface device containing data storage. The entire apparatus and may draw power from the laptop's battery, the PDA's battery, a power source within the dedicated interface device, or a power source located on the carriage assembly. The system is not limited to any particular type of power source, data transfer connection, or processor type.
Ring 102 may comprise, for example, machined aluminum with steel support blocks 104, but is not limited to any particular materials of construction. Ring 102 typically has a diameter suitably larger than the objects desired for measurement and has a thickness suitable for providing rigidity and stability while supporting the ring and carriage assembly. A prototype machined aluminum ring was constructed having an outer diameter of 84 cm and a thickness of 1.27 cm.
As shown in
Once the aluminum ring 202 has been completely assembled, threaded anchors 208 may be adjusted to secure the aluminum ring 202 to the tree. Anchors 108 are typically sharpened at their distal ends 110 and are thin enough to avoid interfering with bark surface measurements at input positions, but thick enough to securely anchor ring 102 and any corresponding instrumentation to the tree. The thickness and materials of construction of the anchors are chosen not only to enable support of the instrument but also to prevent deformation while attached to the tree.
One embodiment, not pictured, may comprise a kit comprising the carriage assembly and related control and processing electronics as described herein, in combination with a series of rings of varying diameters, preferably machined from aluminum or molded from lightweight fiberglass. The rings may have a difference of approximately six inches between their inner and outer diameters, and may come in an increment of sizes beginning at roughly 15 inches in the inner diameter and reaching as large as 30 or 40 inches in the inner diameter. Such a kit will permit use of the measurement apparatus in connection with trees or other objects of varying diameter.
To operate the system, the ring is attached to the tree, the carriage placed at an arbitrary starting point, and the apparatus activated. The controller/processor causes the motor to move the carriage around the ring while the laser diode or line generator projects a beam or line onto the object in the center of the ring to be measured. The camera captures image data from the measurement region, and the controller/processor triangulates the range to the object through the location of the laser light in the image data. This image data is then transmitted back to the controller/processor and stored. The servo motor drives the carriage around the ring incrementally while taking and recording a distance measurement at each increment, pursuant to the flowchart shown in
The flowchart shown in
For distance measurement using a triangulation methodology, the controller/processor receives images from the sensor, finds the brightest pixel, and triangulates distances from it. As measurement depends on the laser point containing the brightest pixel, it may be preferable to shield the measurement area from any sources of bright or direct light during operation. To ensure consistent measurements of bark microrelief, it may be preferable to use the instrument under uniformly overcast skies to minimize subcanopy radiation flux that may interfere with the camera recognizing the laser signal. The ring of the invention should preferably be positioned orthogonal to the tree using a level, to ensure accurate and precise measurements.
The carriage assembly may be connected to the controller/processor via a hardwired connection or a wireless connection. Both the motor and the camera may be connected to the laptop, PDA or dedicated interface device through independent USB cables, which may need to be kept from tangling or pulling out. In the alternative, wireless connections and an independent power source connected to the carriage may be provided. In one embodiment, using an RF link or similar wireless telemetry device, a microcontroller residing on the carriage may transmit the range and incremental position to a nearby interface device being used by the operator. The interface device may include a processor capable of receiving the data, correcting for the ring size and range to target, and plotting the data on the screen for the operator as it is being received. The interface device may then save the data and the plot when the measurement is complete.
In alternative embodiments, other methods of calculation may be used to determine the range of the target, including but not limited to single laser time of flight, scanning beam laser triangulation, scanning beam laser time of flight, structured light, motorized touch probe, ultrasonic/infrared ranging, binocular stereo depth mapping, optic flow mapping, photogrammetric coordinate measurement, or any other method of calculation for an automated distance measurement that is known in the art.
In one experimental example, the data corresponding to the range measurements made by the device were saved in the form of raw, comma-delimited ASCII files. Each entry recorded included the laser rangefinder's triangulation distance and the position on the ring. A computer was used to process the data by subtracting the rangefinder measurements from the ring diameter and plotting the result in polar coordinates. A ±1° mean-point filter was then applied to reduce noise in the data while preserving the shape of the surface. The software used for processing the data also allowed the operator to perform a quick visual check to make sure the data was complete before disassembling the ring from the tree. Typical operation of the invention will provide a detailed cross section of the tree bole in less than fifteen minutes, including instrument set-up.
Sampling resolution is important for quantifying bark microrelief. If the tree bole profile is thought of as a discrete signal, the Nyquist frequency is the critical sampling frequency which must be met or exceeded in order to capture all components of the system. The Nyquist frequency is defined as double the maximum frequency component of the system. In distance-based signal systems, like a tree bole profile, this means that the spacing between sampling points should be half of the width of the smallest ridge the instrument is intended to capture. For a tree bole cross-section, as measured by the instrument described by Yarranton, the angular distance between sampling points is 2°. Thus, the narrowest ridge Yarranton can theoretically detect is 4° around the instrument's central axis. For a 10 cm diameter tree, the most narrow measurable ridge is 0.34 cm, while a 40 cm diameter tree's most narrow measurable ridge is 1.4 cm. The disclosed invention reads a measurement every 0.33°, making it possible to measure ridges 6 times smaller than the Yarranton design. Using a laser rangefinder and a servo motor and controller for positioning shortens data collection time and enhances data quality by reducing opportunity for human error. Computer-controlled positioning allows for increased sampling resolution without increasing the human effort needed in the data collection process. Furthermore, this instrument can be utilized to record tree bole cross sections in multiple locations along the trunk, providing some element of three-dimensionality in the estimation of bark surfaces.
Thus, embodiments of the present invention differ significantly from the Yarranton device as summarized in the following table:
A polar graph comparing measurements of bark microrelief between the automated instrument and the digital calipers demonstrates that the instrument provides a robust and accurate measure of bark microrelief with a mean absolute error of only 0.83 mm as shown in
One measure of quantitative bark microrelief is the ratio of a tree bole's estimated bark area (cm2) (the path length of the cross-section multiplied by the thickness of the bark) to cross sectional area (cm2) (the area occupied by the tree bole). The path length cross section is acquired by the instrument described herein and bark thickness can be acquired by a standard bark thickness gauge. This measure of bark microrelief has utility to a broad scientific community as it provides a meaningful metric to gain a more holistic understanding of the functional ecology of forest ecosystems.
Validation data demonstrates that the disclosed invention is accurate to <1 mm. Polar resolution is 0.33°, which is roughly 2 mm along the prototype ring. This is a greater resolution than can be achieved by hand. Because of this enhanced resolution and measurement accuracy, data provided by this instrument for measuring bark microrelief supplies researchers with a level of characterization that has been previously unavailable.
The instrument for measuring bark microrelief was validated on several utility poles and several species of trees. As shown in
This application claims priority to U.S. Provisional Application Ser. No. 61/178,708, filed May 15, 2009, which is incorporated herein, in its entirety, by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61178708 | May 2009 | US |
