Data Collection Flashcards
What are the stages in data collection projects?
Planning, preparation, collection, post processing, and evaluation.
What is known as primary data collection?
Data collected from direct measurement.
What is known as secondary data collection?
Data collected by using existing data
What is the primary data collection technique for raster data?
Digital Remote Sensing
What are the secondary data collection techniques for raster data?
Scanned maps/airphotos and Digital Elevation Models.
What are the primary data collecting techniques for vector data?
GPS and survey measurements
What are the secondary data collection techniques for vector data?
Topographic surveys and place locations (lat,Lon) from gazeteers.
What are the characteristics of surveying?
Locations are determined by angle and distance measurements, common for cadastral maps, construction/engineering.
What are the characteristics of GPS?
Uses satellite geometry to determine position of a point on earth’s surface.
How is secondary data captured?
Through a collection of raster and vector data from maps, photographs, plans, etc.
What does Spector secondary data capture involve?
Digitizing
What are the three types of digitizing?
Raster-to-vector conversion, manual, and “heads up”
What are the properties of raster-to-vector?
Consistent, semi-automated, but requires substantial user intervention in some cases
What are the characteristics of “heads-up” digitizing?
Directly on computer screen, source data scanned maps/documents or remote sensing, user must georefrence the base data.
What is known as rectification?
The rearrangement of locations to correspond to a specific (geographic) reference system.
What is known as registration?
The rearrangement of locations in one dataset to correspond with the same locations in a reference data set.
What are the steps in the process of differential transformation (“rubber-sheeting”)?
- Define a set of ground control points 2. Fit a mathematical model to describe the relationship between the source and reference component of the GCPs as location
What are the steps in the process of non-linear transformation (“rubber sheeting”)?
- Define a set of gcps. 2. Fit a function (model) to transform the base data into some coordinate system.
What makes a good GCP?
Temporally consistent, easy to identify, and well distributed.
What is the Route Mean Square Error?
The square root of the sum of the squared deviations between the source and reference components of GCP.
What are the digitized features of interests?
Nodes and Vertices
What is a node?
The start and endpoints of a line
What is a vertice?
Points in between the nodes that define a shape.
What are the human errors in digitizing?
Dangles, switchbacks, overshoots/undershoots, silver polygons.
What is a spaghetti data model?
A collection of points that lack topology.
What is known as topology?
The relations used to validate the geometry of points, lines, and polygons.
What does topology focus on?
On qualitative information.
What are the primary topological relations?
Connectivity, Orientation, Adjacency, and Containment
What is the vector data structure?
Node/arc/polygon topology
What is known as arc-node topology?
A table defining points in a line
What is known as arc-poly topology?
A table defining arcs in a polygon.
