3 raster & vector formats

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3 Raster & Vector Formats

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  • Electronic Charts: Raster and Vector Formats

  • DIGITAL SPATIAL DATA

    RASTER

    VECTOR

    Real World

  • The Basic Difference

    Raster charts are simply bitmap images created by scanning a paper chart

    Vector charts portray charted features as points, lines, or areas with amplifying information (attributes) found in an associated database

  • Raster Data Definition

    8 4 6 12 11

    12 2 3 6 0

    3 4 9 9 4

    8 5 10 3 16

    4 7 5 15 10

    A data type that stores

    information as cell values in a

    rectangular grid. A cell is often

    referred to as a picture element

    (pixel)

    6 C C B E

    B S B A A

    C F E A B

    B 5 10 3 16

    4 B B 15 10

    Integer

    Alpha Numeric

    0 1 0 1 1

    1 1 1 0 1

    1 0 0 1 1

    1 0 0 1 1

    1 0 1 0 0

    Binary

    0.2 2.1 0.2 1.1 1.6

    1.3 1.3 1.4 0.6 1.9

    2.1 3.3 0.9 1.4 1.8

    8.6 0.4 2.0 2.1 2.9

    3.4 2.5 8.1 0.5 2.0

    Float

  • Raster Charts

    A set of colored pixels representing chart information as a picture on computer screen

    Simply an array of pixels arranged in rows and columns

    Pixels are color coded, but do not represent features explicitly

  • The Appeal of Raster

    Looks like a paper chart

    Cheap and easy to produce (scan existing paper chart)

    Runs easily on PC

    World-wide availability

  • An intelligent form of digital geographic data where real world objects are represented by points, lines and polygons. An objects representation is described by attributes and coordinates.

    Examples include:

    Digitized Maps

    GIS Data

    Vector Data

  • Feature Entities

    simple point

    simple line

    simple polygon

    complex

    River Spatial Data

    Attribute Data

    LENGTH WIDTH

    2035.00 25.00

    ID

    1

    2 525.00 18.00

    #1 #2

    A Feature logically consists of both the spatial data linked

    with its attributes in a feature table.

    FEATURE ENTITIES

  • Vector Data

    Spatial Data Analysis

    2 5

    1

    4

    7 6

    Lake

    Features:

    Line Points:

    Connected Detached

    Area Text

    Lake

    Geographic data are separated

    into themes, tiled for speed of

    access and placed on CD-ROM Network Analysis

    30 30 N

    040 40 E 30 30 N

    040 50 E

  • Vector Topology

    Chain# Start Node End Node Left Poly Right Poly

    1 1 3 1 0

    2 3 4 2 0

    3 3 2 1 2

    4 1 2 0 1

    5 4 2 2 3

    6 2 5 0 3

    7 4 5 3 0

    8 6 6 4 3

    2 7 3

    1

    4

    3

    5 6

    1

    2

    3

    4

    8

    1 2

    4 5

    6

    0 (Universe or Outside polygon)

  • Paradigm Shift

    Looks different from a paper chart

    Underlying database allows queries and layer selection

    Zooming reveals detail Complex, expensive, and

    time-consuming to produce Needs more powerful

    computer and expensive display to meet IHO/DoD requirements

  • Raster and Vector Data Models

    Vector Representation

    X-AXIS

    500

    400

    300

    200

    100

    600 500 400 300 200 100

    Y-AXIS

    River

    House

    600

    Trees

    Trees

    B

    B

    B B

    B

    B

    B

    B G

    G

    BK

    B

    B

    B

    G

    G

    G G

    G

    Raster Representation

    1 2 3 4 5 6 7 8 9 10

    1

    2

    3

    4

    5

    6

    7

    8

    9

    10

    Real World

    G

    G

  • Raster Model

    Land

    Shoreline

    Water

    Vector Shoreline

  • Raster vs Vector Advantages and Disadvantages

    Looks like the map./ Standard Appearance

    Dumb Map: Very Little Ability for Automated Analysis

    Less Efficient Storage

    Zoom function restricted by pixel size

    Much Easier/Cheaper/ Faster to Produce

    Approximate look of the map/ User-Defined Appearance

    Smart Map: Can Allow Very Powerful Automated Analysis

    More Efficient Storage of Information

    Zoom function not restricted

    Time/Manpower Intensive to Produce

    NIMA Raster Products NIMA Vector Products

  • Summary

    Raster Chart:

    Scanned chart, represented as row and column of pixels

    Cheap and easy to produce and manipulate

    Vector Data:

    Information in the form of points, lines, and polygons w/supporting attribute database

    More difficult to produce and use, but contains more information and capability

    The future of Geospatial Information

  • ENC, DNC, or RNC????

  • Not all charts are equal.

    Many different formats exist for both raster and vector charts

    Most vector charts are digitized paper charts, thereby inheriting any errors (and possibly introducing some!)

    Countries are producing unique digital charts based on their interpretation of IHO standards

  • ENC

    DNC BSB

    ARCS

    C-MAP

    Navionics

    Transas

  • RNC, ENC, or DNC????

    RNC - Raster Nautical Chart

    a facsimile of a paper chart originated by, or distributed on the authority of, a government-authorized hydrographic office. (IHO S-61)

    ENC - Electronic Navigational Chart means the database, standardized as to content,

    structure and format, issued for use with ECDIS on the authority of government-authorized hydrographic offices (Sec. 2.2, IMO PS)

    IHO S-57 format

    DNC - Digital Nautical Chart

    Produced by NIMA in DoD standard Vector Product Format (VPF)

  • Which is better?

    Depends on your point of view.

    Raster is easier and cheaper to produce, but vector provides much more information and capability to the navigator. Vector is the future.

    NOAA BSB & British ARCs worldwide

    DoD standard is Vector Product Format --DNC. 5000 charts, but carto source

    ENC produced from original source data

  • Cartographic Source

  • Original Source Vector

    Data - Image Source

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