3 raster & vector formats

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