User:Mav/Introduction to GIS notes by maveric149/2002-03-05 Lecture
Introduction to GIS notes by maveric149 2002-03-05 Lecture
Errors
Location errors:
- missing polygons
- distored line
- dangling arcs
- unclosed plygons
- Over shoots and Under shoots - Edited by A.Narayana Murthy.
Topological erros:
false relationships between objects
Spatial data editng
matching linesar features across the border of several maps
- line simplification
- line smoothing
- transfer features between maps
Location errors
superimposition of digital v. hard copy source map
Sources of error
human, scanning and tracing, conversion of coordinates
Topolgical erros
- violate topological convention (dangling node, from an over/under-shoot of line)
- Other examples; unclosed polygon
Process
- constuct topology
- determine tpypes of errors that eist
- remove errors and rebuild topology
- iterate to find al errors
Examples
- removal of dangle length
- setting fuzzy tolerance to make digital line snap to the real world one.
- if you spicifiy too big a tolerance, then other feature may be affected
Edgematching
needed step antime source data has coverage between two adjacent areas.
- select on map to be "edit" coverage and the other to be the "snap coverage.
Non-topological editing
delete, omove, cut and paste (whole polygons)
- each plgon is unconnected to other one in no0topo GIS
- reshaping
- deleting vertex
- adding vertex
- split or merge polygons
Other editing funtions
- line simplification
- line desification adds points to selected line at specified intervals
- line smoothing uses math fucintion to modify existing lines