Geographic Information Systems
Data Input and Editing

Mark Foley
mark.foley@dit.ie

Data Input and Editing

Encoding

Analogue & Digital Data

The data stream

The data stream (continued)

Methods of data input

Digitizing table and PC workstation

Point and stream mode digitizing

Point mode – person digitizing decides where to place each individual point such as to most accurately represent the line within the accepted tolerances of the digitizer. Points are placed closer together where the line is most complex and where the line changes direction. Points are placed further apart where the line is less complex or made up of straight line segments.

Point mode – person digitizing decides where to place each individual point such as to most accurately represent the line within the accepted tolerances of the digitizer. Points are placed closer together where the line is most complex and where the line changes direction. Points are placed further apart where the line is less complex or made up of straight line segments.

Point and stream mode digitizing

Stream mode – person digitizing decides on time or distance interval between the digitizing hardware registering each point as the the person digitizing moves the cursor along the line. Points are placed closer together where the line is most complex only as the person digitizing slows the movement of the cursor down to more accurately follow the line. Points are placed further apart where the line is less complex or made of straight line segments allowing the person digitizing to move the cursor more quickly

Stream mode – person digitizing decides on time or distance interval between the digitizing hardware registering each point as the the person digitizing moves the cursor along the line. Points are placed closer together where the line is most complex only as the person digitizing slows the movement of the cursor down to more accurately follow the line. Points are placed further apart where the line is less complex or made of straight line segments allowing the person digitizing to move the cursor more quickly

Bézier curves and splines

Bézier curves are defined by four points; a start and end point (nodes) and two control points. When using Bézier curves to define curves when digitizing a curve between two points, the control points are used to mathematically determine the arc (path) of the curve on leaving the start point and on arriving at the end point. Bézier curves are used in many vector drawing/drafting packages such as Adobe Postscript.

Bézier curves are defined by four points; a start and end point (nodes) and two control points. When using Bézier curves to define curves when digitizing a curve between two points, the control points are used to mathematically determine the arc (path) of the curve on leaving the start point and on arriving at the end point. Bézier curves are used in many vector drawing/drafting packages such as Adobe Postscript.

Bézier curves and splines

Splines are mathematically interpolated curves that pass through a finite number of control points (e.g. P0–P3). They can be exact (i.e. pass exactly through the control points) or approximating (i.e. pass approximately)

Splines are mathematically interpolated curves that pass through a finite number of control points (e.g. P0–P3). They can be exact (i.e. pass exactly through the control points) or approximating (i.e. pass approximately)

Electronic data transfer

Digitizing software