U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Session 3

Primary Data Sources – Part 1

Survey, Air Photography, Satellite

Imagery, …

Sad News, death of the

Founder of Google Earth• Mike Jones died a week ago, on 18th

January 2021.– https://www.geospatialworld.net/blogs/goodbye-michael-jones-

the-man-who-gave-the-power-of-maps-in-our-hands/

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Georeferencing

• Did anyone investigate the British Library

project?

• Or the other georeferencing sites?

• If you are particularly interested if

georeferencing some historical maps,

email me with some details

– We will investigate at some point in the future

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

From last week• Line-thinning algorithm

– Douglas-Peucker (see animation) :

– http://en.wikipedia.org/wiki/Ramer%E2%80%93Douglas%E2%80%93Peucker_algorithm

– Spurn Head – mark ‘must keep’ in a prepass

• mark points at which curve changes direction

• Don’t worry though if this seems too

difficult! Just follow the storyline!!

– I include it because

• It’s a beautiful programme

• Data reduction is a big theme as we shall see

Tony Harris – C program

(getting there)

Epsilon = 500 Epsilon = 2500

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Maps in Computer Form

• Raster Data– Easy to create using a scanner, and cheap

– A ‘picture’ of the map

– No intelligence, useful as a backdrop

• Vector Data– A ‘map reference’ or (x,y) for every point on the map,

plus some ‘meaning’• Road, river, house, field, wood, school,……..

– Can be held in a database• Can be searched or questioned

• Can tell what is connected to what

• Can be used to make decisions and to solve problems

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Maps are ‘Secondary Data’

• The map is a representation, according to a particular set of cartographic rules or conventions – an ‘interpretation’ of ‘reality’

• It relates to a particular time

• It seeks to serve a general set of requirements

• Map data too valuable to throw away, usually

• But, may be hopelessly out of date or have costs or restrictions associated with usage

• We also have access, increasingly, to ‘Primary Data’.

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Primary Data• Primary data comes direct from source, with no

intermediate ‘interpretation’– Although it may require ‘interpretation’ or ‘processing’ before it

can be used

• Examples from the ‘Real World’ (or ‘Natural World’) include– Survey data

– Aerial photography and Satellite imagery

– Radar and Lidar data

– Sensor Data

• Examples from the ‘Man Made World’ include– Gazeteers of names

– Post code directories

– Cadastres, or ownership records

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Survey Data and GPS

• Surveying began in Ancient Egypt

– Land records, after floods

• Long History

– Wild, Leica, Kern, Zeiss…

– See, for example

– Virtual Wild Heerbrugg

• www.wild-heerbrugg.com/index.html

• http://uk.youtube.com/watch?v=IYFBotHfBnQ

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Classical Surveying

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Global Positioning System

• The GPS uses a constellation of between 24 and 32 Medium Earth Orbit satellites that transmit precise microwave signals, that enable GPS receivers to determine their location, speed, direction, and time.

• Accuracy depends on signal, quality of receiver,. – Smartphones give accuracy ~5 m in open, worse near

buildings.

– Professional GPS gives accuracies of a few cm. anywhere in the world, using 2-frequency/augmentation

• GPS coordinates are <lat,long> on WGS84 coordinate system– Uniform across the globe

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Recall – the Longitude

Challenge (1714)• Determining

Longitude needed

reliable chronometers

• Harrison finally

solved the problem

with H4

• GPS relies on the

precise measurement

of time too!

• H3

H4

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Alternative Global Navigation

Satellite Systems (GNSS)• GPS is controlled by the US Department of Defense

– ‘Selective Availability’ and its cessation (Bill Clinton)

• Russian GLONASS since 1991, refurb’ed from 2001 onwards (large recent investment pushed by Putin)– Cooperation with India

– See http://en.wikipedia.org/wiki/GLONASS

• European Galileo– A planned initiative of the EU and European Space Agency (ESA),

as civil alternative

– Initial €3.4 billion project – still contentious, likely rise to €9+ billion

– Initial operation by end 2016 (was 2013), fully 2020

– See official site at: https://www.gsa.europa.eu/ and watch ‘What is Galileo?’ Video.

Galileo and Brexit• UK investment in Galileo to date ~ €1.2 billion but

continued UK role is restricted

– Issue is over access to the Public Regulated Service

(PRS), an encrypted navigation service used by

government agencies

• UK Government has spent $0.5 billion on buying a

part share in an alternative system - OneWeb:

– https://www.bbc.co.uk/news/science-environment-

55365434

– To provide fast global Internet as well as

alternative GNSS

– Controversial, in competition with Elon MuskU3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

So we have Ubiquitous Rapid

Positioning!?• Nearly,

– Doesn’t work where it can’t ‘see’ the satellites• Indoors, in forests, in heavily built-up areas

– But these restrictions are on the way to being removed

• SatNav systems depend on GPS

• Surveyors, using GPS and handheld computers, can rapidly update map databases

• GPS-enabled smartphones are now the norm– User Generated Content

– Users are being used to correct SatNav data

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Practicalities

• If you have a GPS-enabled phone

– You can navigate by it

– You can save the GPS track of a journey

• May need an app

– Can anyone recommend one?

• Will have a sampling interval (if you sample

frequently you may need some data-thinning!)

• Can display altitude profiles as well

– Your photos are automatically georeferenced

• Can your smartphone show your photos on a map?

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

'Earth sandwich': two men, two slices of

bread and 12,724km of filling

• A class member pointed out this

fascinating story about GPS and precision

mapping on Google Earth:

• https://www.theguardian.com/world/2020/j

an/21/earth-sandwich-two-men-two-slices-

of-bread-and-12724km-of-

filling?CMP=Share_iOSApp_Other

• Speculation – what other possible

solutions exist?U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Mobile Data Collection

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Open StreetMap

• OpenStreetMap (OSM) is a collaborative project to create a free editable map of the world.

• The maps are created using data from portable GPSdevices, aerial photography and other free sources.

• Both rendered images and the vector dataset are available for download under a Open Database Licence– Previously Creative Commons

• Registered users can upload GPS track logs and edit the vector data using the given editing tools. – the map display features a prominent 'Edit' tab and a full revision

history is maintained.

– A rapid action video of recent activity

• OpenStreetMap was inspired by sites such as Wikipedia

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Open StreetMap

• See:

– www.openstreetmap.org

– https://www.opencyclemap.org/docs/

• Mapping of Kibera, Nairobi – the largest informal

settlement in Africa

– http://mapkibera.org/

• Latest blog post - Crowdmapping in the Midst of a Pandemic

– Radio 4 programme

http://www.bbc.co.uk/programmes/b03s6mf0

• Do we have any Open StreetMap users/experts

in the group?

AIR PHOTOGRAPHY AND

REMOTE SENSING

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Aerial photography

• Aerial photography is the taking of photographs of the ground from an elevated position

• Platforms for aerial photography include fixed-wing aircraft, helicopters, balloons, blimps and dirigibles, rockets, kites, poles and parachutes

• Can be direct or oblique

• Contain inherent distortions

– Optical, geometrical, atmospheric,….

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Collection of Stereo Imagery

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

A Modern Digital Photogrammetric

Workstation

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

The Past – Analogue

Photogrammetry

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Uses of Photogrammetry

• To take direct measurements on 2D or 3D

– Depends on accurate registration

• To generate Digital Terrain Models (DTM’s), aka

Digital Elevation Models (DEM’s)

– ‘A digital elevation model (DEM) is a digital

representation of ground surface topography or

terrain. It is also widely known as a digital terrain

model (DTM). A DEM can be represented as a raster

(a grid of squares) or as a triangular irregular network’

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Example - DTM of Italy

• with 40 meters

resolution and

5 meters

accuracy,

generated and

owned by

Compagnia

Generale

Ripreseaeree

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Other ways of Making DTM’s

• From digitised contour maps (now largely historical)

• From LIDAR– See later

• From SRTM– See later

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Orthophotos

An orthophoto or orthophotograph is an aerial photograph that has been geometrically corrected ("orthorectified") such that the scale of the photograph is uniform, meaning that the photo can be considered equivalent to a map. Unlike an uncorrected aerial photograph, an orthophotograph can be used to measure true distances, because it is an accurate representation of the earth's surface, having been adjusted for topographic relief, lens distortion, and camera tilt.

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Digital Orthophoto Production

• A Digital Orthophoto needs

– Camera calibration parameters, like the calibrated

focal length and the coordinates of the camera

fiducials.

– A minimum of three ground positions that can be

identified on the photograph to be rectified.

– A digital elevation model (DEM).

• Nowadays highly automated, both for air photos

and satellite imagery, and joined up to form

‘seamless’ mosaics

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Remote Sensing

‘Remote sensing is the small or large-scale

acquisition of information of an object or

phenomenon, by the use of either

recording or real-time sensing device(s)

that is not in physical or intimate contact

with the object (such as by way of aircraft,

spacecraft, satellite, buoy, or ship)’

- Wikipedia

Our Five Senses

• Which of them are ‘Remote’?

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Earth observation satellites

Earth observation satellites are satellitesspecifically designed to observe Earth from orbit, similar to reconnaissance satellites but intended for non-military uses such as environmentalmonitoring, meteorology, map making etc. Geostationary satellites hover over the same spot, providing continuous monitoring to a portion of the Earth's surface. Polar orbiting satellites provide global coverage, but only twice per day at any given spot

- Wikipedia

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Remote Sensing - Satellites

• Originally developed for military purposes

• Since the end of the Cold War, very detailed (high resolution) imagery has become available for civilian use

• Not optical– Computer-processing needed to make ‘visible’

• Photogrammetry as for air photography– Compensation, registration, mosaicing, measuring

• Tutorial –• https://www.nrcan.gc.ca/maps-tools-publications/satellite-imagery-air-photos/tutorial-fundamentals-

remote-sensing/9309

The Effect of Resolution

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Passive Sensors

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Electromagnetic Spectrum

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Spectral Signature

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

4 Band Multispectral Scanner

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Rendering (or making visible)

• Our retinas can only see the Visible Spectrum (in a more or less standard way)– Panchromatic imagery

• Outside the visible, we have to visualise using ‘false colour’, computer generated– Completely flexible, different false colour schemes

can bring out different aspects

– Multispectral imagery

• Image processing techniques can be used to good effect on panchromatic and multispectral imagery (also fusion of both)

• Cloud cover is a Problem!– Some active sensors can penetrate cloud (eg radar)

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

From Governmental to

Commercial• Initially Remote Sensing satellites were

the preserve of the Military

• After the end of the Cold War, hitherto

secret Russian imagery was sold on the

open market

• This led to the growth of commercial Earth

Observation Satellite (EOS) companies

– The first was the French Spot Image

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

A Huge Range of EOS, seehttps://en.wikipedia.org/wiki/List_of_Earth_observation_satellites

Envisat (ESA) carries an array of nine Earth-observation instruments that gather information about the earth (land, water, ice, and atmosphere) using a variety of measurement principles.

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

High Resolution Imagery• IKONOS from GeoEye was the first hires

satellite (1999) providing publicly available data

• Digital Globe is/was another world leader:

– WorldView-1 provides 50 cm panchromatic.

– Aerial collection at a resolution of 1 foot or better for

major metropolitan areas

– Digital Globe’s satellite and aerial programs collect

over 1 million km2 of imagery per day

• With cutbacks in US DoD budgets the two

merged, and now Digital Globe has been

acquired by a Canadian company (Maxar)!– See: www.digitalglobe.com

Special Purpose Systems• There is currently a big growth in privately-financed

systems providing special purpose positional

information or imagery on demand

– GLOBAL AIR TRAFFIC SURVEILLANCE

• https://aireon.com/services/global-air-traffic-

surveillance/

• Piggybacks on Iridium satellite network,$3 billion

investment

– ROOF AND PROPERTY REPORTS, and much more (40

planes always in the air)

• https://www.geomni.com/about-us

• Acquired a Cambridge-based company in 2016U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Some Uses of EOS Data –

Investigate for yourself• Urban and rural mapping of natural resources and of

natural disasters– Change detection

– Creation of Digital Terrain Models

• Environmental– Land use

– Global warming effects, eg retreat of icecaps

• Agriculture and forestry analysis– Soil erosion, Deforestation, Precision Agriculture

• Mining

• Engineering and Construction

• Archaeology

• Lunar and Planetary!

• Two videos from the EU Copernicus Programme

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

An Example – Land Use

• Well-established techniques for both urban and rural areas

• Classification can be ‘unsupervised’ or ‘supervised’.

• ‘Supervised’ uses known usage samples, then find similar– More reliable

News this week – Counting

Elephants from Space• https://www.bbc.co.uk/news/science-

environment-55737086

• Note that the learning phase is

‘supervised’ (or ‘machine learning’ in

current jargon)

• Still ‘proof of concept’

– I wonder how they will validate/test it?

• Pro – across borders is not a problem

• Con – needs cloud free imagery U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

U3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3

Sites to look at• 15 places to get free Satellite Imagery

– https://gisgeography.com/free-satellite-imagery-data-list/

• Free Satellite Imagery for Investigative Journalists– https://www.geospatialworld.net/blogs/free-satellite-images-for-investigative-

journalists/

• The Canadian Tutorial: Watching over our planet from

Space A kit for kids! Is very good– http://www.nrcan.gc.ca/earth-sciences/geomatics/satellite-imagery-air-photos/satellite-

imagery-products/educational-1

• New Scientist on data for driverless cars

– City maps for Driverless Cars

• Near real-time global weather data– https://earth.nullschool.net/

Next Week• More on Primary Sources of Real-World

Information

– Radar and Lidar

– Shuttle Radar Terrain Mission (SRTM)

– Drones

– Sensor Web

• Man-made World Information Sources

– Gazeteers of Names

– Post Code Directories

– Cadastres, or ownership recordsU3AC Course ‘Maps in the Computer Age’ – Spring Term 2021, Peter Woodsford, Session 3