Getting the Map into the Computer

CENTENNIAL COLLEGE SCHOOL OF ENGINEERING & APPLIED SCIENCE

VS 361 Introduction to GIS

• DATA CAPTURE/COLLECTION METHODS

• COURSE NOTES

Data Collection

Can be most expensive GIS activity

Two broad capture methods

Primary (direct measurement)Secondary (indirect derivation)

Data Collection Techniques

Field/Raster Object/Vector

Primary Digital remote sensing images

GPS measurements including VGI

Digital aerial photographs

Survey measurements

Secondary Scanned maps Topographic surveys

DEMs from maps

Topographic data sets from atlases

Stages in Data Collection Projects

Planning

Preparation

Collection / TransferEditing / Improvement

Evaluation

Primary Data Capture

Capture specifically for GIS use.1. Raster – remote sensing

e.g., SPOT and IKONOS satellites and aerial photography, ,echosounding at sea,

Passive and active sensors

Remote sensing is the science and art of acquiring information about the earth’s surface without actually being in contact with it. This is done by sensing and

recording reflected or emitted energy and processing, analyzing, and applying that information.”

REMOTE SENSING PROCESSSource of Illumination (A) - provides

electromagnetic energy to the target of interest.

Atmosphere (B) - media by which energy travels through from and to target.

Interaction with the Target (C) - after passing through the atmosphere the energy interacts with the target depending on properties of both the target and the energy.

Recording of Energy by the Sensor (D) - after the energy has been scattered by or emitted from the target a sensor collects and records the received energy.

Transmission, Reception, & Processing (E) - the energy recorded by the sensor has to be transmitted to a receiving and processing station where the data are processd into an image (hardcopy and/or digital).

Interpretation & Analysis (F) - the processed image is interpreted, visually and/or digitally to extract information about the target.

Application (G) - in the form of a map, GIS, and decision.

PASSIVE SYSTEMS REMOTE SENSING

Passive sensors can only be used to detect energy when the naturally occurring energy is available. For all reflected energy, this can only take place during the time when the sun is illuminating the Earth. There is no reflected energy available from the sun at night.

Energy that is naturally emitted (such as thermal infrared) can be detected day or night, as long as the amount of energy is large enough to be recorded.

ACTIVE SYSTEMSREMOTE SENSING

Active sensors, on the other hand, provide their own energy source for illumination. The sensor emits radiation which is directed toward the target to be investigated. The radiation reflected from that target is detected and measured by the sensor. Advantages for active sensors include the ability to obtain measurements anytime, regardless of the time of day or season. Active sensors can be used for examining wavelengths that are not sufficiently provided by the sun, such as microwaves, or to better control the way a target is illuminated. However, active systems require the generation of a fairly large amount of energy to adequately illuminate targets. Some examples of active sensors are a laser fluorosensor and a synthetic aperture radar (SAR).

REMOTE SENSING SENSORS:

Aerial Camera

-Black and white aerial photography

-Colour aerial photography

-Colour infrared photography

Satellite

LIDAR and others...

AERIAL PHOTOGRAPHY........

• Aerial cameras are the simplest and oldest remote sensing sensor.• Vertical photography provides ‘snap shot’ of the ground from an

airplane.• Cameras are designed for rapid sequence of photographs while limiting

geometric distortions.• Large format (9”x9”).

AERIAL PHOTOGRAPHY...

• Airplane will fly a pre-determined

route along flight lines to capture

the study at the nominal scale.

• 50-60% forward overlap.

• 15-30% side overlap.

• The overlap ensures complete

coverage and also facilitates

three dimensional (stereoscopic)

viewing.

Electromagnetic waves (light) are radiated through space. When the energy (light) encounters an object, one of three

things occur:

reflection by; or

absorption by; or

transmitted through.

AIRPHOTO INTERPRETATION……..

Analysis of remote sensing imagery involves the identification of various

targets in an image, and those targets may be environmental or

artificial features which consist of points, lines, or areas. Targets may

be defined in terms of the way they reflect or emit radiation. This

radiation is measured and recorded by a sensor, and ultimately is depicted

as an image product such as an air photo or a satellite image.

ELEMENTS OF AIRPHOTO INTERPRETATION...

Recognizing targets is the key to interpretation and data collection. Observing the differences between targets and their backgrounds involves comparing different targets

based on any, or all, of the visual elements of tone, shape, size, pattern, texture, shadow, and association. Visual interpretation using these elements is often a part of

our daily lives, whether we are conscious of it or not. Examining satellite images on the weather report, or following high speed chases by views from a helicopter are all

familiar examples of visual image interpretation. Identifying targets in remotely sensed images based on these visual elements allows us to further interpret and analyze.

AERIAL PHOTOGRAPHY...

Shadow

Pattern

Shape

Use of elements…

SATELLITE IMAGERY…….

A network of satellites put into orbit around the earth to collect environmental data about the earth’s surface. Serve a military purpose and an emerging civilian purpose.

ORBITSSATELLITE IMAGERY... • The orbit is the path of the

satellite path around the earth.

• Satellite orbits are designed to make the best use of the sensors carried by the satellite varying in height, orientation, rotation relative to the earth

Geostationary satellites have orbits that

enable the satellites to observe and collect

data continuously over the same

geographic area. Weather and

communication satellites are

two examples of Geostationary satellites.

LANDSATSATELLITE IMAGERY...

• Launched by NASA in 1972 as the first satellite specifically to monitor the earth’s surface.

• The program was commercialised in 1985.• Satellite carries mult-sensors with different spectral

bands:– Return Beam Vidicon (RBV)– Multispectral Scanner (MSS)– Thematic Mapper (TM)

• Near-polar, synchronous orbits.• Revisit period is every 16 -18 days.• Long life span together with above has generated huge

archive of images.• Swath width of 185 m.

SPOTSATELLITE IMAGERY...

• Launched by CNES of France in 1986.• The program was commercialised in 1985.• Each satellite carries twin High Resolution Visible (HRV) imaging

systems that can be operated simultaneously and independently.• Each HRV has two modes:

– Panchromatic (PLA) mode– Multispectral (MLA) mode

• Near-polar, synchronous orbits.• Revisit period is every 26 days.• Resolutions of 10 & 20m.• Swath width of 60 km. • Has oblique viewing capability that can be viewed

stereoscopically.

Primary Data Capture - Vector

GROUND SURVEYING

MINING

CONSTRUCTION

AGRICULTUREENVIRONMENTAL &

FORESTRY

ASSET MANAGEMENT MILITARY

Surveying………..Locations of objects determines by angle and distance

measurements from known locationsUses expensive field equipment and crews

Most accurate method for large scale, small areas

Total StationPen/Portable PC and

GPS

Examples……

GPS (Global Positioning System)Collection of satellites used to fix locations on Earth’s surface

Differential GPS used to improve accuracy

GPS “Handhelds”geographic coordinates text

photos

audiovideo

GPS…..• Navigation system created by U.S government (NAVSTAR)• Made available for civilian use in 1980• 24 Satellites, work in any weather conditions, anywhere in the world 24 hours a day, and is free!!!!!!!!!

How does it work?

Satellite circle the earth twice daily in a very precise orbit and transmitStream of radio signals travelling at the speed EMR (Electro Magnetic Radiation).GPS receivers pick up this information and…Using trigonometry and triangulation…, and the speed of EMR as a constant, they calculate the user’s exact location.

We are 11,000 mile from the satellite and our location is somewhere on an imaginary sphere with radius of 11,000 miles, and the satellite at the center.

We are 12,000 miles from another satellite. Our location is somewhere at the intersection of the two sphere.

Adding third as in the GPS system locates it at one of two discrete points where the threeSphere intersect. Correct one is easily chosen to get the precise location

Secondary Geographic Data Capture

Data collected for other purposes can be converted for use in GIS.

1. Raster conversionScanning of maps, aerial photographs,

documents, etcImportant scanning parameters are spatial and

spectral (bit depth) resolution

Scanner Raster to vector conversion

2. Collection of vector objects from maps, photographs, plans, etc.

1.Digitizing2. Manual (table)

3. Heads-up and vectorization4. Photogrammetry – the science and technology of making measurements

from photographs, etc.

Digitizer

Other Resources…

• Often geographic data available in text form for free - Delimited and requires importing - Conversion - Add Even theme

• Data clearing houses and Data warehouses

• Internet

ADVANTAGES/DISADVANTAGESMAP DIGITISING...

ADVANTAGES DISADVANTAGES

Paper maps may represent theonly record of the data.

Introduces errors associated withpointing accuracy and stability ofmaterial.

Cost effective as low costemployee may be utilised.

May be labour intensive.

Published maps provideinformation on source of data.

Data may be recorded on paperof unknown source.

Proper scale with georeferencedcoordinate grid on publishedmap.

Map may be schematic in naturewithout stated scale of unknownquality.