Total Station Surveying GIS INTRODUCTION TO GIS A

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 Examples attribute data – elevation values. Harry Williams, Cartography of spatial data 1

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. Harry Williams, Cartography 2

The frame of reference could be a street map…. Harry Williams, Cartography 3

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. Harry Williams, Cartography 4

Raster image Harry Williams, Cartography 5

but what’s wrong with this picture? Harry Williams, Cartography 6

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 Harry Williams, Cartography 7

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. 672343. 7 m. E 3676601. 8 m. N 672155. 6 m. E 3676594. 8 m. N 672154. 3 m. E 3676508. 6 m. N 672340. 0 m. E 3676508. 8 m. N Harry Williams, Cartography 8

These GPCs are added to the image within the GIS… Harry Williams, Cartography 9

The result is the image is now registered – every pixel has spatial coordinates… (note: for accuracy, a large number of GPCs is required). Harry Williams, Cartography 10

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)… Harry Williams, Cartography 11

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The DEM is a continuous surface, so it can be used to: 1. Provide an elevation for any point on the map 2. 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. Harry Williams, Cartography 13

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In the lab today you will use Map. Info GIS* to map the total station survey points onto a registered air photo and then create a DEM from the survey points. *Map. Info GIS is the basis for GEOG 4060/5060 Applied GIS: Map. Info Professional offered in the spring. Harry Williams, Cartography 15

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: 1. Hardware (computer and operating system) Geographic/Spatial 2. Software 3. Data Non-Geographic/Aspatial/Attribute 4. Human Operators and Institutional Infrastructure

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

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

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