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Is 80% Accuracy
Good Enoughpresented by
Charles E. Olson, Jr.Senior Image Analyst
Michigan Tech Research InstituteAnn Arbor, Michigan
Prepared for the ASPRS Semi-Annual Conference, Denver, CO, November 2008
Accuracy can mean different things to different people.
This paper addresses only accuracy of thematic data.
Accuracy can mean different things to different people.
This paper addresses only accuracy of thematic data.
The Interagency Steering Committee on Land Use Interpretation and Classification wrote:
“The minimum level of interpretation accuracy in the identification of land use and land cover categories from remote sensor data should be at least 85 percent.”
(Anderson, et al., 1971).
Accuracy means different things to different people.
This paper addresses only accuracy of thematic data.
The Interagency Steering Committee on Land Use Interpretation and Classification wrote:
“The minimum level of interpretation accuracy in the identification of land use and land cover categories from remote sensor data should be at least 85 percent.”
(Anderson, et al., 1971).
At the time this proposal was made, this level of accuracy was routine and it was essentially a “lowest common denominator” approach.
Washtenaw County Mapping Project
Photo Scale: 1:24,000
Compilation Scale: 1:48,000
Classification Scheme
Based on U.S. Geological Survey Circular 671
Hierarchical to Level IV
Nine Level I Classes
Twenty-eight Level II Classes
Fifty-nine Level III Classes
More than one thousand Level IV Classes
Accuracy
96% at Level II
92% at Level III
How did we do it?
By using all of the Image Interpretation “tools”
Existing maps - sources of existing data about the terrain.
Stereoscopes - viewing the photos and seeing the terrain in 3D.
Scales - for measuring and determining feature size.
Terrain sense - understanding the multiple facets of any terrain.
- animals, especially the human animal
- soils and rocks
- vegetation
- topography
- water
The EIIs - elements of image interpretation
Computer screens are today’s medium of choice
Human interpreters do on their computer screens what we
used to do with paper prints.
But the interpretation process remains the same.
Computer users can drape maps over their image data, can measure and determine sizes, can view the terrain in 3-D, can use the EIIs (but seldom do), and seldom have the broad sense of terrain required of a good interpreter.
Shape Shadow Site
Size Pattern Association
Tone Texture Resolution
Of these nine EIIs, computer-based interpretation algorithms
rely almost completely on just one: Tone
The Elements of Image Interpretation (Olson, 1960)
Shape Shadow Site
Size Pattern Association
Tone Texture Resolution
Of these nine EIIs, computer-based interpretation algorithms
rely almost completely on just one: Tone
The Elements of Image Interpretation (Olson, 1960)
When used with the deductive process that Bob Colwell (1954) called “… the convergence of evidence … “ useful results almost always follow.
Agricultural Fields near Ann Arbor, MI September 11
University of Michigan photo
Map Date: 1954
Photo Date: 1952
What happened to these small “ponds?”
and
Are they significant?
Agricultural Fields near Ann Arbor, MI September 11
University of Michigan photo
Low oblique photos taken in 1983.
Changing Relationships
Rapid growth of computer based interpretation systems has resulted in lowering minimum level of accuracy to 80%.
Cost of computer hardware and software, and the personnel to keep it running, often leaves no funds to do it any other way.
If the computer can’t do it, it can’t be done.
Rapid rise in GIS usage.
As long as it fits neatly into the data base, it’s OK.
Computer processing is often faster than manual processing.
Is that speed really necessary when it comes at the cost of reduced accuracy?
How Much Accuracy Do We Really Need?
Is 80% actually good enough?
The market place says YES.
Clients are willing to buy it.
What is the long-range cost?
A 1% increase can be worth $10 million.
Will providing poorer data to decision makers come back to haunt our profession?
The market says YES,
because clients buy it.
The market says YES,
because clients buy it.
But we can do better.
95% accuracy used to be routine.
The market says YES,
because clients buy it.
But we can do better.
95% accuracy used to be routine.
If we didn’t get 95% accuracy we didn’t get paid.
Thank you for listening.
I will be happy to answer questions if time permits, or after the session is over.
Prepared for the ASPRS Semi-Annual Conference, Denver, CO, November 2008