1. GIS DATA INPUT USING SCANNERS AND DIGITIZERS
Charles Redd & Nathan Miller
Frequently, presenters must deliver material of a technical nature to an audience unfamiliar with the topic or vocabulary. The material may be complex or heavy with detail. To present technical material effectively, use the following guidelines from Dale Carnegie Training®.
Consider the amount of time available and prepare to organize your material. Narrow your topic. Divide your presentation into clear segments. Follow a logical progression. Maintain your focus throughout. Close the presentation with a summary, repetition of the key steps, or a logical conclusion.
Keep your audience in mind at all times. For example, be sure data is clear and information is relevant. Keep the level of detail and vocabulary appropriate for the audience. Use visuals to support key points or steps. Keep alert to the needs of your listeners, and you will have a more receptive audience.
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2. First Some History
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3. The Beginning ?
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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4. Did GIS Make 2,500 plus Years of Documents & Mapmaking Suddenly Obsolete ?
From cave paintings to satellite images
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5. 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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6. 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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7. Manual Digitizing ?
The majority of spatial data entered into a GIS is from manual digitizing.
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8. Manual Digitizing
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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9. GTCO CalComp Sonic Digitizer
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10. Types of Digitizers (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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11. Qualities of a Digitizer
Stability
The ability of the digitizer to maintain a value as the puck remains in one place.
Repeatability
Precision
Good digitizers accurate to inch
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12. Qualities of a Digitizer #2
Linearity
the ability to be within a specified distance of the correct value
Good digitizers are able to have a linearity of inch over 60 inches
Skew
The ability to produce coordinates in a true rectangle.
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13. Digitizing Procedures
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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14. Digitizing Procedures (cont)
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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15. Advantages of Digitizing
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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16. Digitizing Vendors
Altek
Calcomp
Didger
GTCO
Kurta
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17. Problems with Digitizing
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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18. Scanning Technology
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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19. Color Scanning Technology
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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20. Color Scanning Technology
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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21. Scanning Problems
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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22. Scanning Problems #2
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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23. Large Format Monochrome Scanners
IDEAL
Large Format Monochrome Scanners
Model
Price
max dpi
Paper Size
Speed
FSS 4300DSP
$6,675
200
36 in.
15 sec.
FSS 8300DSP
$10,425
800
17 dpi
FSS 12300DSP
$11,925
1200
25 dpi
FSS 18300DSP
$13,425
1800
34 dpi
Super Wide 2250
400
50 in.
3 in./sec.
Super Wide 2251
$14,925
6 in./sec
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24. Model Price max dpi Paper Size Speed ANAtech
max dpi
Paper Size
Speed
ANAtech
Binary & Grayscale Scanners
Evolution 4
$10,000
400
36 in.
200 dpi
Evolution 8
$11,000
800
Evolution Pro
$12,500
200 dpi
High Resolution Monochrome Scanners
1270 Digidot
$50,000
1270
27 in.
Unknown
Eagle 4225
$55,000
2540
42 in.
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25. Model Price max dpi Paper Size Speed Large Format Color Scanners
max dpi
Paper Size
Speed
Large Format Color Scanners
ESC 5010 DSP
$11,175
500
36 in.
36 dpi
FSC 8010 DSP
$14,925
800
48 dpi
Large Format Color Scanners
Colortrac 5480
$31,000
800
54 in.
200dpi
Eagle 6250C
$142,000
1000
62 in.
Unknown
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26. Vendors for Scanners Widecom Scanners Anatech Scanners
Anatech Scanners
Vidar Systems Corporation
Abakos Digital Images
Contex Scanning Technologies
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27. Digitizer or Scanner 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
Hardware less expensive
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28. 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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29. 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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30. Common Spatial Errors 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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31. Data Verification
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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32. Examples of Scanned and Aerial images
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33. Paris 1640
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34. Paris 2000
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35. Notre Dame
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36. 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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37. 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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38. One Eagle 6250C Color Scanner Costs more than two Dodge Vipers
Two $69,225 = $138,450
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