1. 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
ASPRS Guevara – Visual Intelligence Proposed kps Definition Rev 1.14.14
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2. 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.
B.
C.
D.
7 kps will have an effective swath 5051' wide
11 kps will collect a swath 8,043' wide
19 kps will collect a swath 13,280' wide
…and so on.
kps
7
11
19
Width
5,051
8,043
13,280
30%
side lap
2,165
3,447
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:
A
B
C
Traveled
Distance/hour
792,000
792,000
792,000
Width
5,051
8,043
13,280
sq. feet
4,000,550,400
6,370,056,000
10,517,522,400
ASPRS Guevara – Visual Intelligence Proposed kps Definition Rev 1.14.14
sq. miles
144
228
377
Efficiency
1.00
1.59
2.63
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