Raster to Vector, Vectorization

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Raster to Vector, Vectorization

• By Guy Stickler
• Ferris State University

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Definition The process of converting paper maps
into digital files.

• Basically the process of inputting paper drawings
  or documents into an electronic format, such as
  CAD or GIS so that the user has the ability to
  manipulate or view the map digitally. This also
  allows the user to view the image with
  coordinates attached.

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Why is it performed ?

• To assist in the creation of electronic maps and
  drawings that can aid in design and engineering.
• Scanners create Raster images which cannot be
  interpreted by CAD type programs. Thus these
  raster images must be converted into Vector
  images.
• However CAD programs cannot convert raster images
  into vector images, unless assisted by a
  conversion program.

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Know your enemy!

• Surveyors use coordinate geometry and analytical
  computations to construct a subdivision plan. An
  accurate but expensive approach.
• Many counties and cities use the inaccurate but
  inexpensive approach of raster to vector map
  conversion. These parcel maps are available
  on-line.
• To name a few counties
• Newaygo County at http//gis.countyofnewaygo.com/
  GIS/Home.htm
• Montcalm County at http//www.montcalm.org/maps.a
  sp
• Ottawa County GIS at http//www.miottawa.org/CoG
  ov/Depts/GIS/

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Kent County (REGIS project) http//www.gvmc-regi
s.org/
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Raster to vector Process

• Scan the map
• Upload the raster image into your Raster to
  Vector converter for example Raster Design by
  AutoDesk
• Use the coordinates of known points (section
  corners, GPS points) to orient the map.
• Convert map to vector file
• Check for errors and edit/correct these problems.

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There are three basic methods of performing
raster to vector operations.

• Manual
• Semi-Automatic
• Fully-Automatic

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Manual

• This is the most time consuming method.
• It can be the most accurate way to perform
  vectorization.

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Semi-Automatic

• Faster than manual. Slower than fully automatic
• High accuracy is still easily achievable.
• Most vectorization is done with this method.

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Fully-Automatic

• By far the fastest way to perform raster to
  vector conversions.
• Can have a lot of problems with accuracy.
• Multiple Free Programs Available

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Free Raster to Vector Programs Available.

• WinTopo, Raster to Vector Conversion Tool,
  http//homepage.ntlworld.com/heatons/softsoft/wint
  opo/index-free.htm
• AlgoLab, Raster to Vector Conversion Toolkit,
• http//www.algolab.com/r2v.htm
• Trix Systems, TracTrix, Raster to vector
  conversion, http//www.trixsystems.com/tractrix.h
  tml?sourcegooglekwraster_to_vector

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Uses

• Easy method to obtain initial approximated
  coordinates for corners.
• Archiving, can be used to store old maps,
  (Architectural/Mechanical drawings) reduces
  space.
• Digitize old maps, to use as a parcel layer for
  information purposes Not for engineering
  purposes.

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Problem in the Raster to Vector process

• Most software packages cannot recognize corner
  points if they are drawn as circles

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Problem in the Raster to Vector process

• Most software packages will draw a curve as a
  sequence of small line segments

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Problem in the Raster to Vector process

• Distances, bearings and curve information are not
  preserved.

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Conclusions

• Although the raster to vector method is
  inaccurate, and not acceptable for legal purposes
  or appropriate for detailed design and
  engineering work. It is a quick and inexpensive
  method to obtain parcel information.
• Many counties are now providing this parcel
  information on-line.
• Surveyors should be aware of the limitations and
  problems of parcel data obtained through raster
  to vector techniques.