Lecture 2 – Map Projection, Datum GPS and Digital Map Everything in Digital – GPS itself is relying on digital technologies. Fast to transfer and process Digital maps can be made faster and cheaper, also more accurately Availability of mapping software and hardware

Digital Map and GPS Why digital maps are useful for GPS? Finding addresses quickly Finding addresses quickly To show where are you To show where are you Locating nearest service center Locating nearest service center To show driving directions for somewhere you want to go To show driving directions for somewhere you want to go To correct your GPS data collections To correct your GPS data collections To create maps To create maps To help/guide you through the GPS data collection To help/guide you through the GPS data collection

Finding Your Data Where you can find the data you want? Search over internet with google or yahoo Search over internet with google or yahoo You can also use data finder services – You can also use data finder services – gis.unc.edu gis.unc.edu terraserver-usa.com terraserver-usa.com geographnetwork.com geographnetwork.com Library, Government Website etc. Library, Government Website etc.

Typical Map Data Topographic Maps (Digital Raster Graphics - DRG)– have contour lines that trace the outline of the terrain and show elevation. The most popular topographic maps for use within the U.S. are made by ___ The topo maps that show the most detail are sometimes called quad sheets or 7.5 minute maps.

Typical Map Data (Cont.) TIGER – Topologically Integrated Geographic Encoding and Referencing data. TIGER data is free ( DLG – Digital Line Graph Township and Range – has been used since the 1790s to survey public lands in the united states. (PLS)

Typical Map Data (Cont.) MrSID – (Multiresolution Seamless Image Database. It is a file format (*.sid) developed and patented by LizardTech. file formatLizardTechfile formatLizardTech Graphics in SID format are compressed with a lossless compression algorithm. DOQ – (Digital Orthophoto Quadrangle) are aeiral or satellite photography that has been corrected.

Typical Map Data (Cont.) ESRI’s Map data – shapefile, coverage, GRID, geodatabase. ERDAS Imagine – IMG AUTOCAD – DXF

Where We Are? Coordinate Systems A map datum is a mathematical model that describes the shape of an ellipsoid (the earth). Some examples: Clark 1880, 1886 NAD 27, NAD 83 QornoqDjakarta

WGS84 World Geodetic System of 1984 (WGS84) based on the GRS ellipsoid – virtually identical with the NAD83. WGS84’s previous version is WGS72. Prior to NAD83, the most popular datum in U.S. was NAD27, based on parameters determined by Clarke in 1866.

These examples are two common world spheroids used today with their values rounded to the nearest meter. For each spheroid, the difference between its major axis and its minor axis is less than 0.34 percent.

Map Projections (a) Azimuthal (b) Cylindrical (c) Conic. Light source positions, also called perspective positions, play an especially important role in planar projections. ( Different aspects, such as polar, equatorial, or oblique, will also affect the map projection )

Map projections distortion The conversion of geographic locations from a spherical coordinate system to a flat surface causes distortion. The projection process will distort one or more of the four spatial properties listed below. Distortion of these spatial properties is inherent in any map. Shape Area Distance Direction

The Universal Transverse Mercator Coordinate System UTM projection has been used by several coordinate systems: Part of the civilian UTM system – USGS, 1977 Part of the state plane system (SPC) And the military grid It has been used for mapping: Most of United States Many other countries The planet Mars

State Plane Coordinate System