Lecture 5 - Spatial Database Development | CSS 4200, Study notes of Agricultural engineering

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CSS 4200

Geographic Information Systems Lecture 5: –^ Spatial Database Development

Database Issues in GIS

•^

GIS applications often require spatial queriesand searching– Contiguity– Connectivity– Containment– Visualization

•^

Need to consider temporal issues

•^

Generally separate GIS data layers

Primary Data Collection

• Other field surveys

• many types of data

collected using site visits,tallies, interviews, etc.

• require careful attention to

sampling design

Secondary Data Collection Methods

• Text Entry• Coordinate Geometry (COGO)• File conversion• Manual digitizing• Automated digitizing

Tablet Digitizing

•^

Tablet digitizing requires a person to entercoordinate information through the use of a

digitizing

tablet

and

digitizing puck

• A

digitizing tablet

is a hard surface with a fine electrical

wire grid under the surface.

• Digitizing tablets are either firm, more stationary tables

or rollup boards designed for portability.

• A

digitizing puck

is an electrical device with cross hairs

and multiple buttons to perform data entry operations.

• An operator then enters the information using the puck.

Getting the Map in the Computer

Convert hardcopy map toelectronic form throughmanual digitization

Convert hardcopy mapelectronic form using on-screen digitizing or digitalorthophotograph

Condition of sourcedocument is veryimportant

Tablet Digitizing – how it works

•^

When the user places the digitizing puckover a location on the tablet, and pressesone of the buttons, the wire meshbeneath the tablet records the location ofthe puck.

-^

Digitizing tablets are very accurate, withmore expensive tablets able to measureobjects to within 0.006 mm.

-^

The coordinate, as referenced by thetablet is then stored in the computer.

x,y

Heads-up Digitizing

-^

Similar to regularmanual digitizing

-^

Done with a mouse on-screen– Generally with an

image in thebackground

-^

Usually less precise

-^

Usually faster

Digitizing – heads up digitizing

-^

Heads up digitizing is a combination of scanning andmanual digitizing.

-^

The main steps in heads up digitizing typically include:–

Scanning the map

• a user can scan the map at a high resolution. -^

Geo-referencing the map

• using mathematical transformation

methods, the user can enter control points on screen andtransform the scanned image to real world coordinates.

-^

Digitizing the map

• the user can zoom to specific areas on

screen and trace points, lines, or polygons on the map. Becausethe maps are already in the correct geographic coordinate systemanything digitized on top of the map will also be in the correctcoordinate system.

Advantages of ‘Geodatabases’

•^

Faster performance

, at times by a factor of 100 or more in

interactive GIS operations as compared to older architectures.

-^

Reliable

, conflict-free editing of complex data in a multi-user

environment.

-^

Freedom

to choose almost any DBMS vendor (as long as

they can support the spatial data types).

-^

Heterogeneous

, free form utilization of Enterprise servers.

•^

DBMS safety

. If the DBMS crashes while working on an

Enterprise project the project is still safe and can be savedwith no loss of data.

-^

Network fault tolerance

. If the network crashes while

working on an Enterprise project the project is still safe.

-^

Ability to use Internet.

The high bandwidth requirements of

older architectures mean that connecting over Internet to aremote DBMS is not usually realistic.