Getting the Map into the Computer CENTENNIAL COLLEGE SCHOOL OF ENGINEERING & APPLIED SCIENCE VS 361 Introduction to GIS DATA CAPTURE/COLLECTION METHODS COURSE NOTES Getting the Map into the Computer

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 Evaluation Editing / Improvement Collection / Transfer

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 PROCESS Source 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 SYSTEMS REMOTE 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... 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. 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.

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... Use of elements… Shadow Shape Pattern

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. ORBITS SATELLITE 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.

LANDSAT SATELLITE 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. LANDSAT SATELLITE 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. SPOT SATELLITE IMAGERY...

ENVIRONMENTAL & FORESTRY Primary Data Capture - Vector GROUND SURVEYING MINING ENVIRONMENTAL & FORESTRY AGRICULTURE CONSTRUCTION ASSET MANAGEMENT MILITARY

Pen/Portable PC and GPS Surveying……….. Locations of objects determines by angle and distance measurements from known locations Uses expensive field equipment and crews Most accurate method for large scale, small areas Examples…… Total Station Pen/Portable PC and GPS

GPS (Global Positioning System) Collection of satellites used to fix locations on Earth’s surface Differential GPS used to improve accuracy GPS “Handhelds” text geographic coordinates photos video audio

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 transmit Stream 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 three Sphere 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 conversion Scanning of maps, aerial photographs, documents, etc Important scanning parameters are spatial and spectral (bit depth) resolution

Raster to vector conversion Scanner Raster to vector conversion Digitizer 2. Collection of vector objects from maps, photographs, plans, etc. 1.Digitizing 2. Manual (table) 3. Heads-up and vectorization 4. Photogrammetry – the science and technology of making measurements from photographs, etc.

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/DISADVANTAGES MAP DIGITISING...