Charles Redd & Nathan Miller
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 GIS was born in Canada in the 1960’s to manage Canada’s large natural resources.
 The success of the merger of computers, database, and mapmaking was a big success.
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Did GIS Make 2,500 plus Years of
Documents & Mapmaking
Suddenly Obsolete ?
From cave paintings to satellite images
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Hard Copy Data with GIS
Significance
• Maps
• Aerial Photos
• Tables of spatial information (coordinates)
• Tables of Non-spatial information attributes
• Engineering and Architectural plans
• Land and Geological Surveys
• Caveman Drawings? Maybe
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How can we use pre-GIS data and non-digital data in our GIS
• Digitize existing graphical information!
– Some of the first methods to digitize graphical information involved overlaying the map with a grid marked on a clear sheet of Mylar.
Information that was within each grid was visually observed and entered by keyboard into the GIS.
• Attribute data from existing tables was hand entered.
• There must be a better way!
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The majority of spatial data entered into a
GIS is from manual digitizing.
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• The digitizing tablet and table allow information to be traced from an existing map or graphic.
• Three different types of tables or tablets exist.
– (1) Acoustic – the digitizing pen emits a high frequency sound that is received by microphones at the corners of the work area, triangulation is used to calculate the x and y coordinate of the pen.
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(Continued)
• (2) Resistivity uses two charged pads separated by a thin air gap, x and y coordinates are determined when the pads make contact.
• (3) The most widely used in large scale digitizers is the electronic digitizing tablet.
Embedded below the surface of the table or the tablet is a grid of wires that measure the strength of the signal from the puck or the pen
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– Stability
• The ability of the digitizer to maintain a value as the puck remains in one place.
– Repeatability
• Precision
• Good digitizers accurate to 0.001 inch
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– Linearity
• the ability to be within a specified distance of the correct value
• Good digitizers are able to have a linearity of 0.003 inch over 60 inches
– Skew
• The ability to produce coordinates in a true rectangle.
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• The Map is fixed to the digitizing table.
• Three or more control points are digitized.
– Easily identified points (intersections of major streets, major peaks, points on coastline)
– These coordinates will be known or verified
– The digitizing area is registered to the map area.
• Digitizing the map can be done in two ways.
– In point mode , the operator identifies the points captured explicitly by pressing a button.
– In stream mode the points are captured at regular intervals (time or distance)
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• Point mode is done subjectively by the operator (no two operators will digitize the same).
• Stream mode generates a large number of points, many of which will be redundant.
• Most digitizing is done in point mode.
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• Low initial capital cost
• Flexible and adapts to different types of data
• Easily mastered skill
• Digitizing devices are reliable
• Generally the quality of data is high
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• Altek
• Calcomp
• Didger
• GTCO
• Kurta
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• Paper maps are unstable, they stretch or shrink, sometimes while they are on the digitizing table.
• The accuracy depends on the dedication of the operator and his training and skill.
• Accuracy also depends on the quality of the source documents.
• Paper maps weren’t prepared “digitally” correct, but to visually impart information, for example if railroads, highways and tunnels pass through a mountain pass the pass may be drawn larger to accommodate the drawing.
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• Converts paper maps into digital format by capturing features as cells, or pixels.
• Cells are captured using a scanner head made up of photosensitive cells.
• Advanced large format scanners have heads with 8000 photosensitive cells
• Each sensor is able to record a pixel rated between 0 (black) to 255 (white) and any graytones between.
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• Color images use the same technique but the image is scanned for red, blue and green.
• Older scanners required the image being scanned to pass the scanning head in three passes.
• Vectorization often requires color scanning
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• Filters allow the head to pass the image once scanning all three colors at once
• The latest technology: full width, single line, sensor array scanning uses a line of
LED’s which capture the image
• LED scanners can create images using
16.8 million colors at speeds several times faster than previously obtained.
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• Higher resolutions aren’t always the answer to better data; often the additional “noise” and resulting clean up of data can cause higher resolution to not be the best solution, a balance between detail and additional manual clean-up must be struck.
• Paper maps are not “dimensionally stable” and a great deal of variation occurs as the maps age.
• Documents must be clean (no smudges or extra marks or lines).
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• Text may accidentally be scanned as line features in automatic feature recognition.
• Specialized symbols (for example marsh or asphalt) may not be detected as such.
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IDEAL
Large Format
Monochrome Scanners
Model
FSS 4300DSP
FSS 8300DSP
FSS 12300DSP
FSS 18300DSP
Super Wide 2250
Super Wide 2251
Price
$6,675
$10,425
$11,925
$13,425
$13,425
$14,925 max dpi
Paper
Size Speed
200 36 in.
15 sec.
800 36 in.
17 sec.@200 dpi
1200
1800
36 in.
36 in.
25 sec.@200 dpi
34 sec.@200 dpi
400 50 in.
3 in./sec.
800 50 in.
6 in./sec
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Model
ANAtech
Binary & Grayscale Scanners
Price
Evolution 4 $10,000
Evolution 8
Evolution Pro
High Resolution
Monochrome Scanners
1270 Digidot
Eagle 4225
$11,000
$12,500
$50,000
$55,000 max dpi
Paper
Size Speed
400 36 in.
800 36 in.
800 36 in.
3"/sec @
200 dpi
3"/sec @
200 dpi
6.4"/sec @
200 dpi
1270 27 in.
Unknown
2540 42 in.
Unknown
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Model
Large Format
Color
Scanners
Price
ESC 5010 DSP $11,175
FSC 8010 DSP
Large Format
Color
Scanners
Colortrac
5480
Eagle 6250C
$14,925
$31,000
$142,000
4/12/2020 max dpi
Paper
Size Speed
500 36 in.
800 36 in.
36 sec.@200 dpi
48 sec.@200 dpi
800 54 in.
1000 62 in.
1.5"/sec. @
200dpi
Unknown
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• Widecom Scanners
– www.widecom.com/
• Anatech Scanners
– www.anatech.com/
• Vidar Systems Corporation
– www.delinfotek.com/
• Abakos Digital Images
– www.abakos.com.au/
• Contex Scanning Technologies
– www.caddcentreindia.com/
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• Scanners
– Speed and ease
– Raster data without intelligence; manual or automatic vectorisation possible.
– Usually produces large files that need compression
– Hardware is expensive
• Digitizers
– Labor intensive
– Requires skilled operator
– Vector (intelligent) data
– Labor intensive
– Hardware less expensive
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Scanning & Digitizing Input Errors
• Incompleteness of the spatial data; missing points, line segments, and polygons.
• Location placement errors of spatial data; careless digitizing or poor quality of the original source.
• Distortion of spatial data; base maps that aren’t scale correct over the entire image or from material stretch in paper maps.
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Scanning & Digitizing Input Errors
#2
• Incorrect linkage between spatial and attribute data; misplaced labels or unique identifiers being assigned during manual key entry or during the initial setup.
• Attribute data is wrong or incomplete; missing data records or data records from different time periods.
• Redundant information, including vertices, text, nodes, and arcs.
• Incorrect label information and placement.
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• Slivers or gaps in the line work.
• Dead ends, dangling arcs, overshoots and undershoots.
• Bow ties or weird polygons caused by inappropriate closings of connecting features.
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• Visual review; usually done by reviewing a check plot (hard copy).
• Cleanup of lines and junctions; this process is usually done by software and then through manual editing.
• Check source maps, if additional copies of the same map are available compare them to see if stretching of the map has occurred.
• Check output drawing to see if text or symbols were read as features if software is used to convert the drawings.
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Summary of Presentation or….
Things I Learned Preparing this
Report
• Scanning while initially faster may not be the fastest solution for your data input.
• Source information needs to be carefully assessed before a method of data conversion is selected.
• The skill and motivation of staff should be evaluated before a method is selected.
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Summary of Presentation or….
Things I Learned Preparing this
Report #2
• Acoustic or Sonic Digitizers Exist
• Digitizing can be as accurate as .001 of an inch
• Color scanners are needed for automatic vectorization
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One Eagle 6250C Color Scanner
Costs more than two Dodge Vipers
Scanner $142,000
Two Vipers @ $69,225
= $138,450
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