Point of Beginning - October 2009 - (Page 40)

fromthegroundup | BY MARK E. MEADE, PE, PLS, CP Change in the air. As I walk out the front door of our office each evening, I pass by a pile of boxes set for overnight shipping. I am always amazed that a typical day includes between 10 and 20 packages, with considerably more heading out during our peak season. All contain different types of geospatial data that are ready for use by our clients for a multitude of applications. But it’s not just the numbers that continue to surprise me; I am also somewhat amazed at how our delivery system has evolved over the last several years. of pavement for a roadway or the limits of a sidewalk, our clients want to view the actual road or sidewalk in an image so that they can make inferences well beyond simply the physical location of the road. In addition to location, they want to see important qualities like pavement type, surface conditions and physical appearance. A similar argument could be made regarding buildings in a mapping project. An image contains significantly more information than a closed polygon that only represents the building footprint. In addition to the added information, digital orthophotos can have a significant advantage over planimetric maps in terms of considerably reduced project costs if planimetric feature compilation is reduced in lieu of an orthophoto deliverable. Horizontal accuracy is not sacrificed in digital orthophotos; accuracies here should be similar to planimetric maps created from the same controlled imagery. But these improvements come at a cost in terms of data storage. Where a typical planimetric map for a 5,000-foot by 5,000-foot tile might be measured as a few megabytes, an uncompressed color digital orthophoto of the same area at a 6-inch pixel resolution would be around 300 megabytes. At 335 megabytes per square mile (a 5,000-foot by 5,000-foot tile contains 0.90 square miles), it doesn’t take long to accumulate a lot of digital data on an orthophoto project. LiDAR is also a contributing factor in the data explosion. This incredibly capable technology has resulted in a number of large mapping projects for our office over the last several years. One of the primary reasons is cost. Elevation models developed from LiDAR are created at a small fraction of the cost of models developed from stereo compilation of controlled aerial imagery. But the LiDAR sensor is indiscriminate and places the same density of points on the ground throughout the project area regardless of whether the ground is flat, rolling or mountainous. This differs from a traditional mapping approach where the number of ground points placed by a trained compiler would be appropriate for both the amount of undulation in the ground and the required vertical accuracies. Compilers place significantly fewer points in flat or more “predictable” areas and considerably more in areas with substantial and unpredictable elevation change. This task is labor intensive, but it results in an efficient digital elevation model that, special section: mapping D Digital orthophotos co contain significantly m more information th than planimetric lin line maps and can al also be less costly if planimetric fe feature compilation is reduced in lieu of an orthophoto de deliverable. Ten years ago, Mylar or paper plots were a required deliverable for virtually all of our projects. Today, I'm not sure I could even find a roll of Mylar for one of our plotters. What’s more, I can’t remember seeing a shipping tube in the last 18 months that would accommodate the plots in an outgoing delivery stack. Delivery tubes in our office have been replaced with DVDs and, more frequently today, portable hard drives. In fact, more than 350 portable hard drives were shipped from our office last year, and those totaled more than 200 terabytes of storage. Also, understand that these numbers were compiled for just one of our office locations, not across the entire enterprise. The Data Explosion M Mark E. Meade, PE, PLS, CP, is PE vice president of vi Photo Science in its Ph Lexington, Ky., office. L So what has changed in this profession to result in such a significant shift in the way we deliver the results of our professional efforts? For one, detailed planimetric line maps have been replaced, for the most part, with digital orthophotos. Instead of interpreting two lines that represent the edges OCTOBER 2009 | Point of Beginning | www.pobonline.com http://www.pobonline.com

Table of Contents for the Digital Edition of Point of Beginning - October 2009

Point of Beginning - October 2009
Web Site/Digital Edition Contents
Editor’s Points
Control on the Edge
Hurricane Watch
The Need for Speed
A Digital Desert
31 Degrees of Latitude
Taming the Wild GIS
The Magic Bullet
From the Ground Up
Professional Topography
Safety Sense
The Business Side
New & Notable
Classified Ads
Fun & Games
Ad Index

Point of Beginning - October 2009