GIS + GPS

Geographic information systems

computer based function used to capture, store, analyze, and display spatial or geographic data (uses layers of data, each layer has a different theme)

5 Components of a GIS

hardware, software, data, workflow, people

Uses for GIA

-cartography

-data management

-spatial analysis

Vector

crisp, realistic model not as good for data analysis

Raster

each cell has a single value for attributes you are collecting

High resolution

cells are smaller (more cells)

Low resolution

cells are larger (less cells)

Pros of raster data

some functions only run in raster, raster data is continuous

Cons of raster data

large data size = slow processing, resolution can reduce detail

Pros of vector data

small data sizes= fast loading, points are an accurate foundation of data

Cons of vector data

sharp boundaries between features, can be misleading for natural features

Where can you obtain GIS data?

digitizing, GPS, field survey, remote sensing

GPS applications

1. querying

2. analyzing

3. displaying

4. outputting

Querying data

searching and filtering, uses SQL (structured query language)

Buffers

-euclidean

-network

Euclidean buffers

creates a uniform buffer around a feature

Network buffers

applied through a medium (road, river, rail line), not in a straight line ex. Google maps

GPS

location finding and data network that bases data on a satellite, receiver measures distance from satellite to your location, the satellite broadcasts signals with accurate time information

Examples of GPS applications

military, space travel, agriculture, construction, mapping, public safety, utilities, transportation

3 parts of a GPS

-satellite (space segment)

-ground control (control segment)

-receivers (user segment)

Satellite

signals are captured by any ground receiver, composed of a computer, atomic clock, and a transmitter (GPS has 24 satellites and orbits 2x a day)

Ground control

made to communicate with the satellite (can be spoofed by the DOD)

Receivers

made to communicate with satellite

C/A Code

initial signal that a GPS receiver reads, long term orbitals, approximates location (ex. almanac)

P Code

more precise and complex, somewhat restricted use, short term orbital data critical for real-time data (ex. ephemeris)

Two way

uses two delays that naturally occur in signal transmission to determine the range between two stations (ex. speed radar)

One way

measurement of the travel time of a signal from transmitter to receiver w/ separate clocks (ex. counting time between lightning and thunder)

Trilateration

similar to triangulation, need 4 satellites for accurate ground location

Timing error

satellite clock drift (atomic clock can experience noise and drift), receiver clock offset (value used to adjust clock is wrong 

Ephemeris

actual orbit is off predicted orbit (can’t fix)

Atmospheric delay

signal refraction; signals have light and can bend

Receiver circuit noise

some level of noise always contaminates observations as static or hissing

Multipath error

signals bounce off objects before they are captured by receivers (most common source of error, can be fixed by using a directional antenna)

Satellite geometry

arrangement of SV in relation to the receiver, the further apart they are, the higher the position accuracy (DOP and PDOP)

Differential correction

improves location accuracy, electronically moves points after the survey is taken