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GIT 214 > 10 - Spatial data input > Flashcards

10 - Spatial data input Flashcards

1
Q

Cheap vector data

A
  • Shapefiles lacking topological relationships
  • Comprise digitizing errors & attribute errors too
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2
Q

Cheap raster data

A
  • Coarse scale vs fine scale (i.e. spatial resolution)
  • Temporal resolution (landscapes change over time)
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3
Q

NGI custodian

A
  • Aerial photos
  • National roads
  • Main/ secondary roads
  • Place name areas
  • Land use
  • land cover
  • Geodesy
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4
Q

SANSA custodian

A
  • satellite
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5
Q

SANRAL custodian

A
  • National roads
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6
Q

PG custodian

A
  • Main/ secondary roads
  • place name areas
  • Land use
  • Land cover
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7
Q

LA custodian

A
  • Main/secondary roads
  • Dwellings
  • Land use
  • Land cover
  • Land parcels
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8
Q

Stats SA custodian

A
  • Place name areas
  • Dwellings
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9
Q

ESKOM custodian

A
  • Dwellings
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10
Q

NGI custodians

A
  • Place name areas
  • Trig beacons, TrigNet
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11
Q

PG custodian

A
  • Land use
  • Land cover
  • Cadastre
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12
Q

SG custodian

A
  • Land parcels
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13
Q

Cadastre meaning

A

an official register of the quantity, value, and ownership of real estate used in apportioning taxes.

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14
Q

Geodesy

A

the science of accurately measuring and understanding the Earth’s geometric shape, orientation in space, and gravity field

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15
Q

Primary raster data

A

Digital remotely sensed images (satellite, aerial photos)

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16
Q

Secondary raster data

A
  • Scanned maps
  • Scanned aerial photos
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17
Q

Primary vector data

A
  • GPS
  • Field survey
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18
Q

Secondary Vector data

A
  • Topographic maps
  • Data Digitizing
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19
Q

Data encoding (digitizing/ key-coding)

A

Converting (attribute) data from a non-digital (analog) to a digital format

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20
Q

Measures for map preparation

A
  • Taped securely in centre
  • Flat, no wrinkles
  • Table adjusted for each reach
  • Planning & organization
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20
Q

3 steps of data encoding process

A
  1. Geocoding
  2. Add attributes
  3. Quality Assurances
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21
Q

Methods of data encoding

A
  • Digitizing (Manual = Tablet & HUD OR automatic stream
    mode)
  • Keyboard, COGO – typing from keyboard (mainly attributes;
    occasionally co-ordinates)
  • Scanning
  • Direct file transfer, file conversion
  • Remote sensing images
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22
Q

Manual digitizing

A

Human guided capture of features from a map image or source.
2 methods:
- on-screen digitizing
- hardcopy digitizing

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23
Q

Stream mode

A

nodes captured at a set rate per time unit – speed at which the cursor is moved determines the number of points captured. (Faster = less, slower = more)

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24
Q

HUD

A

Heads up digitizing

25
Q

Disadvantage of automatic digitizing

A

Need lots of cleaning after scanning is completed; especially removal
of non-target features.

26
Q

3 types of scanners

A
  1. Large-format feed (most common)
  2. Flat bed (usually too small)
  3. Rotating drum (high accuracy, slow)
27
Q

Advantage of automatic digitizing

A

cost-effective for capturing
very large volumes of data

28
Q

Process triangulation

A

Methodological triangulation is the process of using multiple methods of data collection (usually 3 satellites)

29
Q

GPS definition

A

A system of earth-orbiting satellites that provide location (in lat/long
coordinates) and time information in all weather conditions, anywhere on or near the Earth where there is an unobstructed line of sight to
four or more GPS satellites

30
Q

Space segment

A

Constellation of 24 -32 satellites ➔ Arranged in six equally-spaced orbital planes @ altitude of 20 183km

31
Q

Control segment

A
  • Monitor stations
  • Tracking, monitoring, updating and synchronizing SV’s (Space vehicles)
32
Q

User segment

A
  • GPS Receivers
  • Applications
  • Software
33
Q

Trilateration

A

GPS receiver measures the distances to satellites using radio signals. Trilateration = distance
Triangulation = angles (using travel time of radio signals)

34
Q

GLONASS

A

Russian

35
Q

Galileo positioning system

A

EU & ESA (European space agency)

36
Q

COMPASS navigation system (Beidou-2)

A

China

37
Q

IRNSS (Indian regional navigational satellite system

A

India

38
Q

GPS vs GNSS

A

GPS - single satellite system with 31 satellites
GNSS -89 satellites from all 4 systems

39
Q

The 4 satellite systems

A
  1. GLONASS
  2. Galileo
  3. Beidou-2
  4. IRNSS
40
Q

Accuracy of consumer grade

A
  • 15-30m
41
Q

Accuracy of mapping grade

A

-1-5m

42
Q

Accuracy of survey grade

A
  • sub-m-cm
43
Q

Consumer grade example

A
  • Garmin
    -Magellan;
    no post-processing available
44
Q

Mapping grade examples

A
  • GeoExplorer III
  • CMT Mach III;
    post-processing or real-time
45
Q

Survey grade example

A

Trimble post-processing or real-time

46
Q

Orbital error

A

Caused by the satellite oscillator not being synchronised to true time (GPS time).

47
Q

Satellite-based uncertainties

A
  • Clock (orbital) error = 1 m
  • Positional error (ephemeris)
48
Q

Ephemeris def

A

Tabulation of computed positions and velocities of an orbiting body at specific times.

49
Q

Errors due to signal propagation (scrambled signal)

A
  • Atmospheric delay error = up to 11m
  • Multipath error (buildings) = 0.5 m
50
Q

Multipath error

A

Caused when direct signals from satellites are mixed with those reflected from objects in the vicinity of the antenna

51
Q

Received-based uncertainties

A
  • Clock bias
  • antenna centre
  • noise
52
Q

Clock bias def

A

The weakness of gravity makes the clocks in the satellites appear to run faster than the clocks on earth by about 45 microseconds a day.

53
Q

Antenna (phase) centre error

A
  • APC does not coincide with the antenna’s physical center
  • Varies with elevation, azimuth, intensity of the satellite, and frequency of the incoming signal.
54
Q

What causes noise errors?

A

Malfunctioning or incorrectly configured transmitters,

55
Q

Error measurements

A
  • PDOP: Position Dilution of Precision (3D)
  • TDOP: Time Dilution of Precision
  • HDOP: Horizontal Dilution of Precision (Latitude and Longitude)
  • VDOP: Vertical Dilution of Precision (Height)
56
Q

GPS for SA

A
  • Datum = WGS84
  • Reading (position) format = DMS
  • Projection = Geographic
  • Country = South Africa
  • Time Zone = Other
  • UTC offset = +02:00
  • Time format = 24 hour
  • Units = metric
  • North ref = true
  • Direction display = Cardinal Letters
  • 12 channels, has a reading-averaging function, and
  • can export data through a download cable
57
Q

Temporal resolution

A

The amount of time
needed to revisit and acquire data for the exact same location.
- high TR = revisiting delay is low
- low TR = revisiting delay is high

58
Q

Data validation

A
  1. Attribute accuracy
  2. Logical consistency
  3. Completeness
59
Q

Attribute accuracy

A

▪ Wrong value in an attribute field
▪ Missing attribute
▪ Misspelled work or other typographical error
Fix: Sort attributes (~ Excel and check visually) & Run queries

60
Q

Logical Consistency

A

▪ Does the data make sense ?
▪ Do water pipelines connect at nodes?
(logical interpretation and validation of spatial data)

61
Q

Completeness

A

▪ Are all land-use parcels represented in the parcel layer?
▪ Is there any portion of the data missing ?

GIT 214 (16 decks)

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