Who are our clients?

Beyond our own in-house work, we record historic structures as a consulting service primarily to other architects, engineers and other professionals in the preservation industry. We have also frequently contracted directly with developers, institutions and building owners. Frazier Associates has measured, recorded, and analyzed dimensional data for dozens of National Historic Landmark buildings.

What is photogrammetry?

As defined by the National Center for Preservation Technology and Training, photogrammetry is "the science to derive 3-D object information from a set of photographs". Simply put, photogrammetry is a tool to make reliable measurements from photographic images. Its advantages over measuring by hand are manifold - including increased accuracy, the ability to measure off-site, and the ability to collect a vast amount of information in a small amount of time.

What is laser scanning?

Laser scanning is a method of collecting three dimensional data by emitting light which bounces off of objects and thereby determines their placement. Laser scanning offers similar advantages to photogrammetry when compared to hand measuring.

How are photogrammetry and laser scanning alike?

These technologies offer architects a way to capture existing conditions data that is both faster and more accurate than traditional hand measuring. Both use light to determine the locations of existing forms and record these locations in what is known as a "point cloud." Yet while their differences in the field are considerable, these two technologies are both used to produce the same type of deliverable - an architectural drawing.

How are photogrammetry and laser scanning different?

The most striking difference between photogrammetry and laser scanning are in the other deliverables that each makes available beyond a CAD drawing. A few significant differences...

	Orthophotos created by photogrammetry are true digital photographs; orthographic images created from laser scans are images composed from a point cloud (i.e. not photographic in quality.)
	Point clouds produced through photogrammetry consist of carefully chosen points numbering in the hundreds, while laser scans produce point clouds with measurements that number in the millions, often creating a data management issue.
	When creating measured drawings using photogrammetry, the challenge is to select the right set of points to measure, when creating a drawing from a laser scan, the challenge is to sort through the data to locate which are the correct points to use to base drawings on.

Either way, these technologies remain tools in the process of creating drawings and other types of documentation. Neither can replace the critical decision making process and graphical judgments that lie at the heart of our consulting service. We often urge our clients to choose not between the means of production but between the quality of deliverables.

What is a hybrid drawing?

A hybrid drawing is what you get when you combine measured line drawings in vector format with photographic imagery in raster format. In AutoCAD™ software, hybrid drawings consist of DWG files with BMP, TIF, or JPG files attached to them in such a way that the resulting images reflect the same spatial conditions as the lines and polylines in the CAD drawing.

What is a vector drawing?

These are comprised of points, lines and arcs as defined by mathematical vertices. It is the basic language for CAD programs like AutoCAD™.

What is a raster image?

This is an image that is composed of a series of pixels. This is what you get when you scan (or digitize) a paper image. Raster images are what digital cameras produce. It is the basic language for imaging programs like Adobe Photoshop™.

Witherspoon Hall, Princeton, NY		The Irem Temple, Wilkes-Barre, PA		The Gilmore Cabin, Orange County, VA
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