Data Capture GIS

Primary Data Capture

first hand observations

Secondary Data Capture

getting data from existing source

GNSS (Global Navigation Satellite System)

used to determine geographic positions anywhere on earth

Space Segment

network of satellites that give signals to earth

Control Segment

ground stations that track satellites, and adjust clock timings

User Segment

equipment on earth to process satellite signals to find precise position

Pseudorandom Code

a code transmitted to show receivers signal arrival time

Ephemeris Data

data about the satellite’s current orbital position and trajectory

Almanac Data

Information by satellites about orbit and status details

Time Difference of Arrival (TDOA)

distance (from sender to receiver) measured based on time delay of a signal

Trilateration

determines relative position using distances from known points

Dilution of Precision (DOP)

Measuring how satellite position impacts the accuracy of calculations

Selective Availability (SA)

Degradation of civilian GPS discontinued

Differential GPS (DGPS)

system uses ground bases stations to broadcast error connections

Spatial Resolution (DPI)

measure of raster image in dots per inch

Color Depth

number of bits used to make a color for pixel

Georeferencing

connecting spatial data to a known geographic coordinate system.

Ground Control Points (GCPs)

Real world features to anchor spatial datasets to absolute map coordinates

Affine Transformation

mathematical transformation that preserves straight lines and parallels

Root Mean Square Error (RMSE)

The positional error between source coordinates and transformed target coordinates

Rectification

reprojecting a raster image into a georefernced spatial data set

Heads-Down Digitizing

tracing map features on a physical tablet

Heads-Up Digitizing

tracing directly over georefernced raster images on computer

Inflection Points

key points along a curve, critical during digitizing

Cartographic Generalization

simplifying map detail to maintain clarity

Spatial Metadata

the credit of sources used