Copyright : Hi Tech Criminal Justice, Raymond E. Foster Police Technology Police Technology Chapter Five Police Technology Geographic Information

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Learning Objectives Understand: Basic parts of a map and how they are used Basic parts of a map and how they are used Theory of trilateration in conjunction with time difference on arrival (TDOA) Theory of trilateration in conjunction with time difference on arrival (TDOA) How global positioning satellites operate. How global positioning satellites operate. Difference between a map and a geographic information system Difference between a map and a geographic information system

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Introduction For law enforcement, geography refers to: Distance between two objects Physical characteristics of those objects Could be natural terrain, streets, locations or even people Screen capture provided by Pen-Link™ Inc.

Copyright : Hi Tech Criminal Justice, Raymond E. Foster GIS Basics A combination of: Computer hardware Computer hardware Computer software Computer software Data Data Which enables people to create visual displays of information

Copyright : Hi Tech Criminal Justice, Raymond E. Foster GIS is a relational database designed to help store, organize, and use spatial information. GISs are a combination of technologies that enhance our understanding of geography. GIS Basics

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Cartography Basics Cartography is the science of map making. Cartography is the science of map making. A map is a visual representation of a defined space. A map is a visual representation of a defined space. Orientation Grid lines Latitude Longitude Waypoint

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Cartography Basics An area of California - An area of California -LatitudeLongitude

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Trilateration is the foundation of most Automatic Vehicle Location technologies. Trilateration is the foundation of most Automatic Vehicle Location technologies. Trilateration is similar to triangulation Trilateration is similar to triangulation If you are 25 miles from Joe’s House, you are somewhere in the circle

Copyright : Hi Tech Criminal Justice, Raymond E. Foster If you are 25 miles from Joe’s House, and 15 miles from Bob’s House, you are somewhere in the area of the circles’ overlap Trilateration

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Trilateration Add the distance to Jane’s house, and you are where all three circles overlap

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Global positioning satellites (GPS) use trilateration with a second math formula to provide users with location. Global positioning satellites (GPS) use trilateration with a second math formula to provide users with location. A GPS system uses an RF receiver and a network of satellites. A GPS system uses an RF receiver and a network of satellites. Final component is a ground control station: Final component is a ground control station: Four monitoring stations Four monitoring stations One control station. One control station. Global positioning satellites

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Global positioning satellites 1978, U.S. launched twenty-four satellites in orbit. By 1994, they were operational. 1978, U.S. launched twenty-four satellites in orbit. By 1994, they were operational. These completed the Dept. of Defense These completed the Dept. of Defense Navigation Satellite Timing and Ranging (NAVSTAR) system. Drawing courtesy of the United States Navy

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Global positioning satellites The GPS system uses trilateration and Time Difference on Arrival (TDOA) to give a precise location. Satellite orbits are predictable Satellite orbits are predictable Their probable location is known in advance Their probable location is known in advance Info on prediction of orbital path is in an almanac (a software database) Info on prediction of orbital path is in an almanac (a software database)

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Time Difference on Arrival (TDOA) Radio waves travel the speed of light – a constant. Radio waves travel the speed of light – a constant. By measuring the time it takes a radio wave to reach a receiver we can calculate the distance from the source to the receiver. By measuring the time it takes a radio wave to reach a receiver we can calculate the distance from the source to the receiver. With three signals (three satellites) we can use trilateration to determine location With three signals (three satellites) we can use trilateration to determine location

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Global positioning satellites The job of the monitoring stations and the master control stations is: Track satellites Detect deviations from predicted orbital paths Recalculate orbital path in cases of deviation Update almanac info every six hours

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Possible errors in GPS: Orbital deviation (satellites affected by Earth’s gravity) Orbital deviation (satellites affected by Earth’s gravity) Clock drift – corrected by TDOA Clock drift – corrected by TDOA Atmospheric conditions – GPS transmissions affected by ionosphere and troposphere. Atmospheric conditions – GPS transmissions affected by ionosphere and troposphere. Department of Defense (selective availability) Department of Defense (selective availability) Global positioning satellites

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Back to GIS Geographic Information Systems are used by police agencies to analyze crime. police GISs use one of two alternative methods: Universal transverse mercator (UTM) Universal transverse mercator (UTM) State plane coordinates State plane coordinates

Copyright : Hi Tech Criminal Justice, Raymond E. Foster UTM divides the world in 60 zones, each containing 6 degrees of latitude. UTM divides the world in 60 zones, each containing 6 degrees of latitude. The location of an object is measured in meters from one of the corners of the zone and the longitude The location of an object is measured in meters from one of the corners of the zone and the longitude Universal Transverse Mercator

Copyright : Hi Tech Criminal Justice, Raymond E. Foster State Plan Coordinates A system that divides the U.S. into more than 120 zones.

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Spatial Data In a GIS system, the features (objects) of a map become spatial data. We can: Analyze info about a location Analyze info about a location Specific info about the object itself Specific info about the object itself Analyze information about its relationship to other features mapped in the GIS system. Analyze information about its relationship to other features mapped in the GIS system.

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Three kinds of data contained in a GIS system: Points, Lines, and Areas A GIS system combines points lines and areas to map complex objects like buildings, roads, or political jurisdictions. GIS Basics

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Final feature is areas or polygons. Areas are defined by a continuous boundary that surrounds a certain feature (zip codes, city limits, etc.) Areas are defined by a continuous boundary that surrounds a certain feature (zip codes, city limits, etc.) A discrete site (a specific location) can be a park, mall, or housing project. A discrete site (a specific location) can be a park, mall, or housing project. GIS Basics

Copyright : Hi Tech Criminal Justice, Raymond E. Foster What makes GIS different from traditional maps is the ability to add information about the features (tabular data) for analysis. Attribute – traits or quality of a feature Attribute – traits or quality of a feature (color, number of ports, size of units, etc.) Value – a predefined answer that limits possible responses to attribute. Value – a predefined answer that limits possible responses to attribute. GIS Basics

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Image Data is a third type of data found in maps created with GIS technology. Aerial photographs Aerial photographs Scanned photographs Scanned photographs Can link tabular data (parolee address info) and image date (photographs of parolees) GIS Basics

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Getting the Data GISs do not contain maps or graphics. They create visual representations of relational databases. Events entered into a GIS database must be geocoded. Events entered into a GIS database must be geocoded. Geocoding is the process of determining the proper coordinates of an event’s location (usually an address) Geocoding is the process of determining the proper coordinates of an event’s location (usually an address)

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Getting the Data Basic street address information for GIS applications can be obtained from both: Basic street address information for GIS applications can be obtained from both: Commercial sources Commercial sources Government sources Government sources Data on crimes and specific location is usually input by the agency.

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Final part of GIS process is the application of GIS tools for display and analysis of the database. Pin maps Pin maps Using different symbols for different types of events Using different symbols for different types of events GIS Basics

Copyright : Hi Tech Criminal Justice, Raymond E. Foster Automatic Vehicle Location Law enforcementLaw enforcement agencies using GPS for Law enforcement AVL can improve the accuracy of the GPS system with differential correction. Stationary source of GPS receiver’s location Stationary source of GPS receiver’s location Compare signal Compare signal Remove distortion Remove distortion Photograph provided by Woodcrest Vehicle Center

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