1 ASPRS Guevara – Visual Intelligence Proposed kps Definition Rev 1.14.14

On kps – kilo pixel swath By Dr. Armando Guevara – www.visualintell.com @wherescience www.linkedin.com/pub/armando-guevara/b/3a2/987/

1. - Concept definition and proposal

In an effort to clearly guide customers’ decision when considering buying a

sensor the time has come to establish a digital measure that reflects simply

sensor collection capacity per unit of time.

The term “frame” (as used in the aerial film paradigm) no longer makes sense in

the digital world and is increasingly confusing to the end customer. When

evaluating a new camera, vendors will show up with very large frame, large frame,

medium frame systems, and they are all different sizes. The term “megapixel” can also

be confusing since it is not a clear metric of mapping collection capacity; further,

CCD (coupled charge device i.e. the imaging sensor) aspect ratio used in by the sensor

system, depending on how it is oriented along-track, can deliver different radiometric

and geometric quality results.

With sensor evaluated attributes all being equal “apples to apples”- i.e. all have the

same image geometric and radiometric quality, performance, reliability, ease and

speed of workflow etc., a pivotal selection criteria is the cost of ownership and

operating cost; both of which are impacted by collection cost. A key efficiency of

collection metric/attribute is defined by: “At a required GSD, how much area can

be collected in a given unit of time”. The answer to this is effectively defined by

the swath of the sensor in number of pixels.

2. - Introducing “kps”

A kps is the number of pixels across track covered by a sensor, in other words, the

number of pixels in the swath. 1 kps = one thousand pixel wide swath.

Example: collect at 1 foot pixels (30 cm) –impact of kps

2 ASPRS Guevara – Visual Intelligence Proposed kps Definition Rev 1.14.14

3. - kps - a base measure to establishing digital aerial camera collection efficiency

It is often difficult to differentiate the competing claims of different digital aerial camera

manufacturers when it comes to efficiency. There are many aspects that contribute to the

efficiency, but one simple measure is for the same aircraft speed, how much area is collected

per hour of flying?

There are many factors that impact the cost of a successful aerial metric geoimaging

project, including but not limited to camera focal length, CCD size and flying height. For digital

cameras, the project is designed for a specific nominal ground sample distance or GSD. No

matter what flying height, focal length, or CCD size, the amount of area covered is the

nominal GSD times the number of pixels in the selected width of the CCD array (x or y

orientation – typically the largest number of pixels on the CCD is in x so if more depth is

desired the CCD can be rotated with x becoming y).

Normal block collection of a project will factor in a 30% side lap between flight lines.

Examples of pixels swath with “CCD configurations” of:

A. 7 kps will have an effective swath 5051' wide

B. 11 kps will collect a swath 8,043' wide

C. 19 kps will collect a swath 13,280' wide

D. …and so on.

30%

kps Width side lap

7 5,051 2,165

11 8,043 3,447

19 13,280 5,691

In a project example with a flying speed of 150 miles an hour times 5,280 feet in a mile,

the aircraft travels approximately 792,000 feet an hour. Efficiency results for the above kps

example are shown on the following chart:

Traveled

Distance/hour Width sq. feet sq. miles Efficiency

A 792,000 5,051 4,000,550,400 144 1.00

B 792,000 8,043 6,370,056,000 228 1.59

C 792,000 13,280 10,517,522,400 377 2.63