1. Total Station Surveying & GIS.
Harry Williams
Total Station Surveying & GIS.
INTRODUCTION TO GIS
A Geographic Information System is a combination of software and hardware that can store, manipulate, analyze and display geographic information.
What is geographic information? Any information that has spatial coordinates (can be mapped).
The total station data collected last week falls into this category. It has spatial coordinates (UTM) and attribute data – elevation values.
Examples of spatial data
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Earth Science

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We could simply display the total station data in the GIS, but this would clearly be improved by having some frame of reference that we can recognize.
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The frame of reference could be a street map….
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Or, something increasingly popular is to use an air photo as a back drop. This
particular image is a raster image consisting of colored pixels (cells) – a jpeg.
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Raster image
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but what’s wrong with this picture?
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It’s oriented around the right way now (we are used to having north at the top of the page), but the pixels that make up the image still do not have spatial coordinates… N
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Giving spatial coordinates to an image is called image registration and it’s achieved by using Ground Control Points (GCP). A GCP is a point that can be seen on the image and for which we know the spatial coordinates. To demonstrate, I collected 4 GCPs with a GPS.
mE mN
mE mN
mE mN
mE mN
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These GPCs are added to the image within the GIS…
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The result is the image is now registered – every pixel has spatial coordinates… (note: for accuracy, a large number of GPCs is required).
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Digital Elevation Models (DEMs): a DEM is a raster coverage (a map made up of cells or pixels), wherein every cell has an elevation value. The elevation values are usually calculated by interpolation from a number of spot heights within the map area. For example Inverse Distance Weighting (IDW) Interpolation gives weights to spot heights based on the inverse of their distance from an unknown point…(in other words, the closer the spot height is to the unknown point, the more weight or influence it has on the calculated elevation for the unknown point)…
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The DEM is a continuous surface, so it can be used to:
Provide an elevation for any point on the map
Be used to construct topographic profiles
The following example is from a Geography Masters thesis – it is a DEM of coastal wetlands in Trinity Bay, Texas, including some topographic profiles.
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In the lab today you will use MapInfo GIS* to map the total station survey points onto a registered air photo and then create a DEM from the survey points.
*MapInfo GIS is the basis for GEOG 4060/5060 Applied GIS: MapInfo Professional offered in the spring.
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16. Geographic Information Systems (GIS)
GIS are computer programs that allow users to store, retrieve, manipulate, analyze and display spatial data
Spatial Data (Geographic data) – any data that represents information about the Earth
GIS components
Recent definitions of GIS suggest that is consists of:
Hardware (computer and operating system)
Software
Data
Human Operators and Institutional Infrastructure
Geographic/Spatial
Non-Geographic/Aspatial/Attribute

17. GIS Data Structures
Vector – Made up of points, lines, and polygons

18. GIS Data Structures
Raster (Grids) – Made up of pixels of computer screen

19. GIS Data Structures
DEM (Digital Elevation Model) – Digital terrain representation technique, where elevation values are stored in raster cells