Principles of GIS Lecture #3 PDF

Principles of GIS Lecture #3  This lecture covers... Data sources Data model Vector and raster representations  How to capture spatial data? 2 categories – spatial and attribute Several techniques: Surveying Existing maps (digitizing) Aeri...

Principles of GIS Lecture #3  This lecture covers... Data sources Data model Vector and raster representations  How to capture spatial data? 2 categories – spatial and attribute Several techniques: Surveying Existing maps (digitizing) Aerial photogrammetry LiDAR Satellite imagery UAV (Drones) Censors data  How to capture spatial data? Digitize from existing maps.  How to capture spatial data? Satellite images e.g. SPOT image, Landsat, other military images (very details). Aerial photogrammetry Good for large areas Expensive (big agency or companies) Very accurate data. LiDAR data Good large areas Very accurate data Expensive Produce huge datasets. Unmanned Aerial Vehicle (UAV) (or Drones) Good for small areas Not accurate, thus not for mapping purposes. Meant for reconnaissance survey Note: lots of research to improve the technique for mapping. Mobile mapping Good for mapping of 3D buildings and other 3D features. Very accurate Large datasets Mobile mapping (Google Street View) Good for roads / highway mapping. Meant for visualization and simple mapping. Normally deploy by road navigation companies like Google, Tom Tom, HERE.  How to capture spatial data? Other data sources – contours, – cadastre and other maps, and – many other data Data layers, data models and data structures Data models Data structures  Data model It is a model to describe what we see in the reality (the spatial objects) so that the computer can understand then we produce the related information for any decision making. The objects – houses, buildings, forests, roads, pipes, cables, rivers, water bodies, terrains, etc.  Data model It refers to how we model or represent real world objects in a computer environment.  Data model Map makers or cartographers use points, lines, and surfaces 2D primitives and 3D primitives. e.g. nodes, lines, polygons node line polygon  Points (or nodes) Zero-Dimensional (0-D) features. Point can be used to represent an object like a city, a town, a lamp post, a tree, masjid, etc. (depends on the map scale).  Lines 1-Dimensional (1-D) features. It has length (but no width). However, in reality it may has width. In GIS, we consider length with no width. E.g. roads, pipelines, cables, part of rivers, railways, boundaries (country, state, district) and etc.  Polygons (surfaces) 2-Dimensional (2D) features. It is area-based features. Like forest area, residential area, city area, town area, sea, water bodies, etc.  Bodies 3-Dimensional features. A combination of surfaces and heights. Like 3D buildings, 3D trees, etc.  Vector and raster An object could be represented by vector or raster.  Vector and raster An object could be represented by vector or raster. Raster representation An object could be represented by raster. Based on rows and columns. Each cell may contain various information e.g. coordinates, heights, etc. Vector representation An object could be represented by vector. Widely implemented in many GIS software. Based on discrete objects view. Precise nature of representation, storage efficiency, quality of cartography output, and availability of functional tools e.g. map projection, overlay and analysis. Raster and vector representations Raster and vector  Why vector? Why raster? Vector – offers accurate representations due to the coordinates. However, vector has computational disadvantages. Raster – less smooth representation (jagged- look). Raster offers less computing power, thus, simple and faster processing.  Assignment #1 Prepare one write-up that describes “Why I prefer to represent my GIS objects via raster not vector? However, vector also a nice choice, why is it so?” A report with 1000 words. Submit your report by next Monday at 10.30 am to [email protected] Write down your name and mobile number on the report.  Assignment #1 Your report should: Clearly written, “no cut and paste” kind of sentences. Write by using your own English. Cite your sentences appropriately, and list down all the references that you used (at the end of the report). Any questions?