Fundamentals of GIS

Review:NR 143 Final Exam

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Final Exam: Monday, May 7

10:30-1:15

110 Aiken

Closed book/notes

Fundamentals of GIS

Topics and format

Review of some important, post-midterm material follows.Don’t forget to study spatial reference and data structures!

question topic number points percent

Remote Sensing 10 46 23.0%

Raster Analysis 7 34 19.0%

Public Data 5 23 11.5%

Spatial Reference 3 21 10.5%

Geocoding 3 19 9.5%

Metadata 2 14 7.0%

Data Quality (error) 3 13 6.5%

GPS 3 13 6.5%

TIN 2 9 4.5%

Data Structures 2 8 4.0%

40 200 100.0%

question type

short answer 17 80 40.0%

medium answer 5 40 20.0%

multiple choice 20 80 40.0%

41 200 100.0%

Fundamentals of GIS

Topic detailRemote Sensing

Terms, sensor properties & types of resolution, comparison of sensors, classification techniques, electromagnetic spectrum, spectral response curves….

Raster Analysis

Techniques and their purposes, surface tools, filters, viewshed….

Public Data

Acronyms, important datasets and what is included with each, compare….

Spatial Reference

Projection types, terms & concepts, compare, scale factor, PCS’s….

Geocoding

Components and purpose, different approaches and their result….

Lecture Materials by Austin Troy except where noted © 2008

Fundamentals of GIS

Topic detail continuedMetadata

Why metadata? Sections and components? Terms….

Data Quality (error)

Terms, error types, quantitative vs. qualitative data….

GPS

Satellite system terms, differential GPS, sources of error….

TIN

Purpose(s), creating a TIN, parameters, advantages….

Data Structures

Field types, storage unit characteristics….

Lecture Materials by Austin Troy except where noted © 2008

Fundamentals of GIS

Raster Analysis

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Fundamentals of GIS

Raster dataRaster Elements

–Extent

–# rows

–# columns

–Coordinates

–Origin

–Orientation

–Resolution

–Grid cell

Fundamentals of GIS

Reclassification with Grids

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Here we reclass to 3 classes, based on natural breaks

Fundamentals of GIS

Raster Analysis Overview• Raster overlay queries

– Example: [elevation > 2500] AND [slope > 20]

• Raster overlay calculations– Example: [soil_depth_1990] – [soil_depth_2000]

• Zonal Statistics

• Raster terrain functions (hillshade, slope, aspect, contours)

• Viewshed AnalysisTerrain + Points = Visibility raster

• Neighborhood Statistics & Filters

• Distance Functions & Density

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Raster calculator

Local * Focal * zonal * global

Fundamentals of GIS

Lecture Materials by Austin Troy except where noted © 2008

Viewshed analysisInputs/outputs? Parameters?

In this case, red is for tower 1, blue for 2 and green for 3

Fundamentals of GIS

Lecture Materials by Austin Troy except where noted © 2008

Raster terrain functions in ArcGISHillshade: Slope: Contours: Aspect:

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Illumination / brightness values

Rise / run expressed as percent slope OR as angle (degrees)

Azimuth angle of steepest path (orientation or bearing of the slope direction)

User-defined interval and base contour

Fundamentals of GIS

Zonal Statistics• Summarize the mean, max

or sum for some value within each of the bounding units

• Polygon and Raster• Raster and Raster• Here we summarize by

subdivision zones the mean soil erodibility value (from our calculation).

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Lecture Materials by Austin Troy, Brian Voigt and Weiqi Zhou except where noted © 2011

Fundamentals of GIS

Neighborhood Statistics (Focal)• A method of summarizing raster data within a neighborhood by a

statistical measure, like mean, std dev.

– Neighborhood shape

– Neighborhood settings

• Window size

• Units

– Statistic types

Fundamentals of GIS

Neighborhood FiltersFilter types

– Low pass filters – remove noise (emphasize trends)

– High pass filters – edge enhancement (emphasize local detail)

Fundamentals of GIS

Distance Analysis

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Used to answer questions related to distance

– Proximity

– Straight Line Distance Measurement

– Cost Weighted Distance Measurement

– Shortest Path

Fundamentals of GIS

Density Functions• Use sample points to create density surfaces

• Can use a z value, or it can simply be based on the abundance and distribution of points.

• Output: number of points per unit area of a designated neighborhood

Fundamentals of GIS

Terrain Analysis

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Fundamentals of GIS

• Raster slope is calculated by steepest path in neighborhood• Aspect is direction of steepest path (azimuth in degrees)• Critical for flow path analysis, watershed generation, drainage network and viewshed analysis, etc.• Contour generation

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Slope, Aspect, Contours55 51 48

54 43 36

53 45 38

Fundamentals of GIS

• Triangulated Irregular Network• Irregular distribution of

elevation sample points• Breaklines• Z-tolerance (~resolution)• Delauney triangulation

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Three Dimensional data — TIN

Fundamentals of GIS

• 3D visualization• Extrude a third dimension• Drape thematic layers on elevation• Create animations (fly-through)

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ArcScene

Fundamentals of GIS

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3D Visualization

Fundamentals of GIS

Public Data

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Fundamentals of GIS

GIS Data• Acronyms!

• What’s included? How do they compare? Scale?• USGS National Map

SRTM

NHD

DEMNED

DOQDLGNWIGNIS

NLCD

DRG

7.5 minute

30m resolution

1/3 arc second

HypsographyImperviousness

hydrography NAIP

CLUSSURGO

TIGER

Fundamentals of GIS

The difference between an aerial photograph and an orthophoto

• Aerial photo– image displacement caused

by tilting of camera and terrain relief

– scale is not uniform

– cannot measure distances on a photograph

• Orthophoto– rectified to remove non-

constant scale due to varying distance to camera

– Also adjusts for elevation and tilt

– Therefore possible to measure distances directly like on other maps

– Can serve as a base map onto which other info may be overlaid

Light travels longer distance at scene edge: magnification

Fundamentals of GIS

Geocoding & Digitizing

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Fundamentals of GIS

What is Geocoding?• Convert lists/spreadsheets to features (needs a mechanism to calculate coordinates for the address) • Address matching: uses street address database, created from a streets layer

Address table + reference layer = point features• Reference layer defined in ArcCatalog as “address locator”• Takes advantage of ref. layer attributes & topology (left/right)• Geocoding accuracy = fn(reference layer accuracy)

Fundamentals of GIS

Geocoding example: 1060 Main Street

• Point is placed on even (upper) side of street• Position of 1060 is interpolated

Main St1000 1100

1001 1101

L-F-ADDR L-T-ADDR

R-F-ADDR R-T-ADDR

It looks for Main street, then for the 1000-1100 block

direction

1060 Main St

Fundamentals of GIS

Specify reference file

Specify address range attributes

Specify rules for address list

Specify zone

Geocoding in ArcGISTools >> Geocode addressesArcCatalog:

Fundamentals of GIS

Geocoding and Error

100 m

100 m

300 m

Fundamentals of GIS

Geocoding and Error

A rural area with a long road segment: very imprecise

An urban road segment: smaller, more precise

Rural street segments are also more subject to greater error because longer street segments means more interpolation

Fundamentals of GIS

XY GeocodingWe can also create points from a table by their latitude and longitudeDo this by clicking:

CA hazardous waste sites

• Then we specify the lat and long fields as well as the spatial reference system

• Lat and Long should be in decimal degrees

Fundamentals of GIS

Digitizing

• Tablet digitizing

• Heads-up digitizing

Often “drawing” features over an orthophoto base

Fundamentals of GIS

GPS

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Fundamentals of GIS

GPS• GPS (NAVSTAR): one of two GNSS – Global Navigation Satellite System…. GLONASS is the other…. more coming

• 30 NAVSTAR satellites; need at least 3 to determine location (better to have 4 or more)

r1

r2r3

Fundamentals of GIS

How Does GPS Work?

• We need at least 3 satellites as reference points (better to have 4 or more)

• Position is calculated using trilateration

Fundamentals of GIS

• Calculating range (distance from satellite to receiver)

• Time determined from lag in pseudo-random code, one from satellite and one generated at the same time by the receiver.

• 4th satellite helps with time synch

Source: Trimble Navigation Ltd.

How Does GPS Work?

Sent by satellite at time t0

Received from satellite at time t1

Distance = Velocity * Time

Fundamentals of GIS

Sources of Error• Gravitational effects

• Atmospheric effects

• Obstruction & Multipath

• Satellite geometry…. PDOP

• Selective Availability

Fundamentals of GIS

Locating Satellites

• Need to know satellite locations to determine geometry/PDOP

• Ephemeris and Almanac are part of transmitted signal

Fundamentals of GIS

How does DGPS work?• One stationary & one moving receiver …. error

• The stationary receiver must be located on a known control point …. Correction factor sent to rover

Fundamentals of GIS

Remote Sensing

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Fundamentals of GIS

Electromagnetic Radiation

• Electromagnetic Spectrum

Radiation Source

Irradiance

Wavelength(Micrometers)

Ultra-Violet

Visible Near IR Shortwave IR Midwave IR Longwave IR

Pan

chrom

atic F

ilm

Color Film

.01 .04 .07 1.0 3.0 5.0 14.00 um

Visible comprises 2%of EM Spectrum

Visible

Spectral ImageryIR Film

Fundamentals of GIS

Passive Detection

Camera or sensor

irradiancereflectancescattering

transmittanceabsorption

Fundamentals of GIS

Reflectance

High

Low

Blue Green Red

Ref

lect

ance

0.4m 0.5m 0.6m 0.7m

White LightGreenGreenBlueBlue

RedRed

Fundamentals of GIS

So, what are RS data?

• RS imagery is raster data.

• Each picture element (pixel) has a value, or digital number (DN).

Fundamentals of GIS

Spectral Response Curves50

40

30

20

10

0

0.4 0.6 0.7 0.8 1.3

Artificial turfAsphalt

Fallow field

Sandy loamy Soil

Concrete

REFLECTANCE

(%) Clear water

Wavelength (micrometers)

Grass

Visible0.5

GREENBLUE GREEN RED

Near IR

Fundamentals of GIS

Band Placement

Wavelength, m

Landsat TM

RGB

100

50

0

25

75

Per

cent

Re

flect

ance

Near IR Mid IR

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

Silty-clay soilTurbid river water

Vegetation Clear river waterMuck soil

1 2 3 4 5 7

visible

1 2 3 4MSI

IKONOS & HI RESPAN

LANDSAT 7 PAN

Fundamentals of GIS

Multispectral Display

BLUEBLUE

GREENGREEN

REDRED NEAR IR SHORT

WAVE IRMID-

WAVE IRLONGWAVE IR

1Landsat TM Band 2 3 4 5 7 6

Band Combination = 7 4 2 (LANDSAT)

Color Guns =

Band Composite Output =

Fundamentals of GIS

3-2-1 4-3-2 4-5-2

Landsat band combination comparisons

False color composite

Color infrared composite (CIR)

True (natural) color

composite

Fundamentals of GIS

Sensor Properties• Spatial resolution (pixel size)

• Spectral resolution (# bands)

• Radiometric resolution

• Temporal resolution

IKONOS 4mLandsat 30m

Orthophoto 0.5m

©

Space Imaging

100s of BandsHyper-spectral

Band 2

.53-.62

Band 3

.63-.69

Band 1.45-.52

Visible

Band 4

.79-.90

Band 5

1.55-1.75

Band 7

2.08-2.35

Band 6

10.4-12.4

Near IR SWIR LWIR

1000s of BandsUltra-spectral

Multi-spectral

– bit depth

– orbital period (return rate)

Fundamentals of GIS

Trade-offs

Spatial Resolution ½ m 4m 30m

# Bands 1 4 7

Radiometric Resolution

8 bit 11 bit 8 bit

Temporal Resolution On demand 3-4 days 16 days

Aerial Photo IKONOS Landsat

© Space Imaging

Compare also: SPOT, Quickbird, ASTER

Fundamentals of GIS

Active Sensors• IfSAR – Inferometric Synthetic

Aperture Radar

• LIDAR – LIght Detection And Ranging

received signal

transmitted signal

Fundamentals of GIS

Major Satellite Systems

• High spatial resolution

– Quickbird, IKONOS, OrbView-3, SPOT-5 PAN, IRS-P6

• Medium spatial resolution

– Landsat-5 TM, Landsat-7 ETM+, ASTER, SPOT

• Low spatial resolution

– MODIS, ENVISAT, GOES, AVHRR, MSS

Fundamentals of GIS

Orbits• Most of these satellites are in sun-synchronous orbit

• Satellite passes over the same part of the Earth at roughly the same local time each day

• ~8 degrees inclined from polar orbit, allowing match with earth’s rotation

• Maintains sun angle

Source: http://hdsn.eoc.nasda.go.jp/experience/rm_kiso/satellit_type_orbit_e.html

Fundamentals of GIS

Materials by Austin Troy and Weiqi Zhou except where noted © 2008

Scanners• Pushbroom (along track) vs. Whiskbroom (across track)

• LANDSAT (MSS, TM, ETM+)

• SPOT (HRV)

• IKONOS

• Compare resolution(s), other characteristics

• Off-nadir viewing

Source: http://www.sci-ctr.edu.sg/ssc/publication/remotesense/spot.htm

Fundamentals of GIS

Image Pre-Processing• Create a more faithful representation through:

– Geometric correction

– Radiometric correction

– Atmospheric correction

• Image enhancement

– Spatial feature manipulation: Spatial filtering, edge enhancement, and Fourier analysis…. Low-pass & high-pass filters

– Contrast manipulation: Gray-level thresholding, level slicing, and contrast stretching.

– Multi-image manipulation: Band ratioing, principal components, vegetation components, canonical components…. Orthophoto vs. “true” orthophoto

• Rectification – remove distortion (platform, sensor, earth, atmosphere) …. Scanned aerial photo vs. orthophoto

Fundamentals of GIS

Image classification

• Turn RS data into meaningful information (feature extraction)

• Spectral pattern recognition – supervised vs. unsupervised …. training sites

• Spatial pattern recognition

• Temporal pattern recognition

• Applications – land cover mapping (Anderson classification)

• Accuracy assessment

Fundamentals of GIS

Object-oriented classification: 3 Steps• Segmentation • Feature

extraction

• Classification

Fundamentals of GIS

Object-oriented Classification

BBBB

CCCC

Fundamentals of GIS

Data Quality & Documentation(Error & Metadata)

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Fundamentals of GIS

Data Quality• Accuracy + Precision = Quality

• Error = fn(accuracy, precision)

• Cost vs. quality tradeoff

• Random vs. Systematic error

• Positional accuracy

• Attribute accuracy & precision (quantitative vs. categorical)

SCALE

Which can be controlled?

Standards

Fundamentals of GIS

Other measures of data quality• Logical consistency

• Completeness

• Data currency/timeliness

• Accessibility

Common sources of error?

Fundamentals of GIS

Error ….• Accuracy & Precision

•Positional vs. Attribute Accuracy

•Propagation (single step)

• Cascading (multi-step)

• Cascading error can be managed to a certain extent by conducting “sensitivity analysis” Image source: http://oopslist.com/Conflation (2 types)• Attribute

• Feature

Fundamentals of GIS

Documentation and Metadata

• Purpose?

• Federal mandate…. FGDC (“Content Standard for Digital Geospatial Metadata”)

• Terminology!

Fundamentals of GIS

Documentation and MetadataSome roles/purposes of metadata:

1. Information retrieval, cataloguing, querying and searching for data electronically.

2. Describing fitness for use (applicability) and documenting the usability and quality of data.

3. Describing how to transfer, access or process data

4. Documenting all relevant characteristics of data needed to use it

5. Data permanence; creates institutional memory; advertises an organization’s research (generate partnerships)

Fundamentals of GIS

Materials by Austin Troy © 2008

Documentation and Metadata• Metadata usually include sections similar to these

Fundamentals of GIS

Documentation and MetadataCritical components usually break down into:

1. Dataset identification, overview

2. Data quality

3. Spatial reference information

4. Data definition

5. Administrative information (distribution)

6. Meta-metadata