Measurement Sciences

Objectives

Cartography depends on information collected by other disciplines. The source for a particular map will depend on the purpose of the map and the budget available. Different technologies have an effect on the type of information available and its accuracy. Geometric structure depends on sources, but each of these uses triangles as the root of the technology in some way or another.

Surveying:

Different types: geodetic, land (property), topographic (now less common)

• Ground measurement: direct measurement of angles and distances

• GPS: high accuracy (down to cm) in XYZ; quick answers (military uses real time; geodetic surveying minutes) using timing signals (distance) from satellites

Photogrammetry

Topographic mapping from stereo pairs of airphotos (replaced old "plane table" surveys)
Developed out of military uses in WWI, but first used in civilian TVA
Mechanism: take photographs (9"X9" cameras with calibrated lens)

Photointerpretation:

Use of airphotographs in land assessment
Land Cover: vegetation, flooding, mineral surveys...
Land Use: more human input required to determine actual use

Remote Sensing:

actually should include airphotography, but often restricted to satellite sources
should also include photointerpretation of satellite imagery but often restricted
to digital processing of imagery data....
Classification of images: usually land cover
Stereo satellite coverage.... Photogrammetry from above?

The basic secret: Triangles!

Each method of surveying turns into some kind of triangle, using Euclid's scheme to solve for the parts you don't have...

• Practical demonstration of "plane table" on the overheads
• GPS unit demo after class

Digitizing:

exisiting maps must be measured to convert for the computer.
Manual digitizers measure position on a tablet, operator moves cursor
point mode (one at a time), line following in time or distance sampling
Scanners: hardware to measure positions and follow lines automatically
two flavors: raster (image) scanners, line followers (vector)

Resources for more information:

Surveying

• Geodesy for the Layman (person)
• GPS tutorial at Geographer's Craft Project (now at Colorado);
  

Airphoto

• Aldrich 1979 Review of Remote Sensing capabilities (obsolete for satelites, but fine on airphotos)
• Sources for national airphoto projects (EROS Data Center)
• Digital Orthophoto Quads (DOQs) produced for whole 49 states of USA (Alaska always different...)

Remote Sensing developments

• Shuttle Radar Mission: measured topography between 60 North and 58 South to 30 meters (100 meter version freely available worldwide, 30 m inside USA... maybe by fall 2001)
• Landsat 7: the most recent in a series going back to 1972, now distributed by US Geological Survey
• a more recent (1999) article from Forest Service applying satellite sources
• Terra (NASA platform) supports ASTER and MODIS.
• Earth Observing System (EO-1) - will it continue? what will happen to the "experimental" Landsat? Is it the Advanced Land Imager?
• SPOT: the French alternative
• Space Imaging Corp. (one of many commercial ventures) has IKONOS 1 meter color images (5 m too) in service, and ready for SALE at their CARTERRA store (Look at some examples)

Version of 9 May 2003