scientific

IUFRO Wind and Trees International Conference, July 31- August 4, 2011 Department of Plant Biology, USDA Forest Service, The University of Georgia

Capturing the Damped Oscillation Paths of Individual Branch Tips Using a Digital Pen Recorder
P.Pickett

Under various wind loads, individual trees are chosen for optimal wind exposure. The tips of branches are fitted with digital pens, which draw ink lines tracking branch tip paths, capturing the movement over time.

This work is part of a long-term interdisciplinary artistic and scientific project, with the aim of capturing a more complete and dynamic expression of the array of excitation behaviors exhibited by branch tips as they absorb and release the effects of wind. Experiments begun in 1999 used pen and ink, on paper and photographs of the trees. By 2008, in an attempt to overcome some of the limitations caused by the weight and interaction of the drawing apparatus, video footage of the tree and branch was combined with 3-D tracking software in order to attempt to trace the branch movement, and to capture branch excitation, at a distance.

While research and experimentation continues in order to move beyond the 2-D accumulation of lines, towards a 3-D representation of branches through space; the digital pen recordings begin to address the unfolding of time. The resulting digital file, will “replay” the “drawing”, as it has been created over time, along with an accompanying soundtrack. In addition, in spite of the digital pen’s weight and analog interaction with paper, it will provide the ability to analyze the direction, amplitude and frequency of the oscillations of the branch during a sudden or sustained gust. Empirical data is noted, including duration, time of day, wind speed, temperature, meteorological conditions, elevation, location and date. To complete the picture, a video is simultaneously made of the entire tree and the selected branch, and synced with the digital drawing in order to compare the effects of the wind on the entire tree with the responses of the individual branch tip.

Bio-mechanics, influence of branches on tree sway, branches of tree as individual damped oscillators

International Conference on Wind and Trees IUFRO August 5-9, 2007
University of British Columbia, Vancouver, BC

Tree Drawings: Recording Wind Conditions
P. Pickett

The following describes a devised method of capturing “drawings” of the movement of branches under a wide variety of airflow circumstances. This graphic model is produced by attaching a pen to the lower branch of a tree and, on a tripod, carefully positioning a drawing surface to best record the resulting marks. Reacting to the wind, branch movement produces patterns that are characteristic of the type of tree, position of branch, leaf shape, wind velocity and direction, surrounding canopy profile, turbulence, terrain, temperature, etc. (Tree identification was taught to me by father, who studied forestry at Oregon State University.) In early experiments, beginning in 1999, designed to make visual models of (usually) invisible forces, I used a convenient backyard pear tree at the Dan Flavin Art Institute, on eastern Long island, in order to record the winds’ effect on trees.

Currently native trees are preferred and locations are chosen based on the prevalence of extreme wind conditions (Paloverde in the Banning Pass, California; kiawe at Makapuu, Hawaii; a grove of aspen near Laramie, Wyoming; krummholtzed (dwarfed) black spruce on Mt. Washington, New Hampshire.) As a general guide I use the NREL wind resource maps. For local conditions I consult NOAA and raw sensor data from the NWS. Once at a location, many hours are spent observing the winds’ relationship to the specific terrain, comparing the predicted wind-speeds with on-site measurements using a Kestrel 4000 anemometer, documenting and photographing examples of thigmomorphogenesis (winds’ effect on tree growth). I then choose a particularly wind affected tree, and a branch whose movements are a good representative of that species characteristic gestures. The duration of a drawing is anywhere from ½ hour to 5 hours. The title of each drawing includes documentation of the conditions (eg, Knobcone pine – 1 hr – winds NW 12-28, gusting to 31 mph – just above the “Old Ridge Route”, Leibre Mtn., Elevation 4500’, Southern California, Sat. May 27, 2007.)

Digital video tracking imagery of tree movement interactions with gusting airflow conditions

P. Pickett
ABSTRACT
In order to trace the movements of trees as they interact with gusting wind in a complex terrain, illustrations are produced using a 3-D tracking program. The animation of specific tree behavior will be based on digital information chosen from within field-gathered footage to show the paths of foliage, branch and tree movement. The biomechanical response of leaves, branches, limbs, canopy, and/or trunk displacement can be captured, and a story told of the effects of gusting wind conditions upon a single tree, and further, over the forest and/or across edge terrain. By choosing tracking points on trees from the entire framed landscape, the response of an individual tree in the foreground can be seen within the context of the surrounding canopy. The trailing imagery can illustrate specific wind loading strategies, and show range of movement from crown to lower branches. Wind speed data are recorded in the field during filming and are provided for each digitally animated, video-captured event. Gust excitation and sway response, as well as the characteristic movements of distinct elements (trees, forest canopy, shrubs, grasses), can be individually expressed in this process using the vocabulary of art.
1. Introduction
Art and science share the need to give visual expression to events, data, forces, ideas – things that might not otherwise be seen. Working between the disciplines, I am interested in the physicality and expressiveness of measurable circumstances, and in the accumulation, over time, of this visual information.
My interest in the effects of wind on trees began in 1999 as part of a series of works designed to expand the definition of drawing to include marks made in response to the stimulation of an external phenomenon. I looked beyond traditional artistic responses to light and its visual effects, to the environment for examples of forces that would only be made visible by their effects and corresponding response characteristics I imagined visual residues accumulating around the branches of trees swaying in the wind.
I began with “Tree Drawings”, in which I attached a pen to the end of a branch and positioned a drawing surface (paper, panel, photo of the tree) below in order to capture the track of the branch movement when excited by the wind. It was an experiment designed to begin to capture the movement of individual branches under a wide variety of wind conditions. Patterns emerged that were at once aesthetically pleasing and informative.
Building upon and proceeding from an analog representation of branch excitation, this digital video-tracking project is designed to more fully realize the original drawing experiments, and to create a more dynamic picture event of tree behavior.
2. Measurable circumstances – the process
What follows is a snapshot of the first steps taken in what will be a long-term motion-drawing project. Video footage is gathered while on drawing expeditions in the field, from a variety of wind conditions and terrains. This process does not require foreign tracking objects to be inserted into the tree. Relying solely on the video footage of the trees for tracking information will allow for the greatest flexibility in capturing the behavior of very tall trees, trees in difficult terrain, trees at a distance, or a larger view of the landscape.
Once in the studio, the footage is sorted and edited. Crucial to the process is finding digital tools that will provide dependable data for the array of compositing programs that will be utilized later in the process to create the most expressive and animated pictures of tree movement. Using a 3-D tracking system, the footage of trees in gusting conditions is analyzed for the best examples of clearly identifiable tracking points.
Set to run automatically, the tracking program chooses 2-D points to solve for motion and, if they exist, to solve for 3-D coordinates. Trails follow tracker coordinates and serve as a tracer-picture of the path of the branch tip, resulting ultimately in the ability to represent the wind-effect-on-trees-event over time. In supervised tracking, each feature is selected manually, monitored and corrected as needed to follow a selected set of pixels throughout the shot. A black and white version allows for easier supervised tracking, especially at lower resolutions.
3. Conclusion
Attempts to “picture” an event in nature, whether by drawing, painting, graphs, diagrams, statistical modeling, measured experiments, or photographic processes: all are but approximations and tell only part of the story. The results of this project promises to continue the conversation between a phenomenon, its recording, and an artists’ response. It will evolve within languages both aesthetic and useful