Transcript Document

GIS DATA INPUT USING
SCANNERS AND
DIGITIZERS
Charles Redd & Nathan Miller
7/17/2015
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First Some History
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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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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
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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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Manual Digitizing ?
The majority of spatial
data entered into a
GIS is from manual
digitizing.
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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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GTCO CalComp Sonic Digitizer
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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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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 0.001 inch
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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 0.003 inch over 60 inches
– Skew
• The ability to produce coordinates in a true
rectangle.
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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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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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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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Digitizing Vendors
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Altek
Calcomp
Didger
GTCO
Kurta
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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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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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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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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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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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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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IDEAL
Large Format
Monochrome Scanners
Model
FSS 4300DSP
FSS 8300DSP
FSS 12300DSP
Price
$6,675
$10,425
$11,925
max
dpi
200
800
1200
Paper
Size
Speed
36 in.
15 sec.
36 in.
17 sec.@200
dpi
36 in.
25 sec.@200
dpi
FSS 18300DSP
$13,425
1800
36 in.
34 sec.@200
dpi
Super Wide 2250
$13,425
400
50 in.
3 in./sec.
Super Wide 2251
$14,925
800
50 in.
6 in./sec
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Model
Price
max Paper
dpi Size
Speed
ANAtech
Binary & Grayscale Scanners
400 36 in.
3"/sec @
200 dpi
800 36 in.
3"/sec @
200 dpi
$12,500
800 36 in.
6.4"/sec @
200 dpi
1270 Digidot
$50,000
1270 27 in.
Unknown
Eagle 4225
$55,000
2540 42 in.
Unknown
Evolution 4
Evolution 8
Evolution Pro
$10,000
$11,000
High Resolution
Monochrome Scanners
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Model
Price
max
dpi
Paper
Size
Speed
Large Format
Color
Scanners
ESC 5010 DSP
FSC 8010 DSP
$11,175
$14,925
500
800
36 in.
36 sec.@200
dpi
36 in.
48 sec.@200
dpi
Large Format
Color
Scanners
Colortrac
5480
Eagle 6250C
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$31,000
800 54 in.
$142,000
1000 62 in.
1.5"/sec. @
200dpi
Unknown
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Vendors for Scanners
• 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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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
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• 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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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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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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Examples of Scanned and
Aerial images
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Paris 1640
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Paris 2000
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Notre Dame
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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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