Introduction to GIS : Basics of Using GRASS GIS Karl Kent Benedict, Ph.D
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Introduction to GIS : Basics of Using GRASS GIS Karl Kent Benedict, Ph.D. Earth Data Analysis Center University of New Mexico Introduction 2 Class Goals • Provide foundation knowledge about Geographic Information Systems (GIS) • Provide hands-on experience with open-source mapping technologies: GRASS and other tools • Provide specific knowledge required to import, integrate with other geospatial data, and visualize output of the DREAM system Introduction 3 Class Organization Introduction GIS Fundamentals Introduction to Linux Building GRASS Data Acquisition and Preprocessing Data Import/Export Data Management Manipulation and Analyisis Product Generation - Visualization Product Generation - Cartography Automation Advanced Topics Recap and Review Introduction 4 GIS Fundamentals 5 GIS Fundamentals A basic understanding of the principles of Geographic Information Systems is required to effectively take advantage of GIS technologies in data management, analysis and visualization applications. This section provides a brief introduction to GIS consisting of the following topics: • What is a GIS? • Key GIS Concepts – Projection – Scale – Resolution • Data Fundamentals – Variable Types – Layer Types • Elements of the GIS Process – Data Acquisition – Preprocessing – Data Management – Manipulation and Management – Product Generation GIS Fundamentals 6 What is a GIS? • A system for managing geographic data. – Information about the shapes of objects. – Information about attributes of those objects. – Spatial variation of measurements across space without reference to specific boundaries – continuous fields of measurements. • A system for analyzing and modeling spatial relationships. – Spatial statistics – Aggregation and reclassification of observation data – Statistical or process model development and implementation • A system for presenting geographic information graphically and in summary – Maps – Tables – Graphs – 2D and 3D animations GIS Fundamentals 7 Key GIS Concepts • Projections and coordinate systems – Define units of measurement (e.g. spherical coordinates [lat-lon], projected coordinates [UTM meters]) – Translate spherical coordinates to cartesian coordinates – Projections may be optimized to retain direction, distance, or area, leading to a need to consider the application in choosing an appropriate projection for a project • Scale – The map scale at which data retain acceptable precision • Resolution – In raster datasets, the size of the pixels in the quantized data representation – Object size, model sensitivity, resolution of source data influence choice of resolution GIS Fundamentals 8 Key GIS Concepts Geographic (Unprojected representation of the analysis region) Transverse Mercator Projection of the same region What projection(s) are commonly used for your area? GIS Fundamentals 9 Data Fundamentals • Data types – Nominal: categories without an inherent order – Ordinal: ordered values without even intervals – Interval: ordered values with even intervals but no well defined zero value (e.g. degrees Celsius) – Ratio: ordered values with even intervals having a well defined zero value (e.g. degrees Kelvin, cm) • Layer types – Vector (point, line, polygon) – Raster (pixels in a regular grid) • Topology – Defines the relationship between spatial objects (e.g. adjacency, direction) GIS Fundamentals 10 Data Fundamentals Samples of Raster Data Elevation Data: Excerpt from a global MODIS Mosaic: GIS Fundamentals 11 Data Fundamentals Samples of Vector Data Cities (Point): European Drainage Network (Line): GIS Fundamentals 12 Data Fundamentals Vector Data Samples (cont.) Country Boundaries (Polygon): Individual data layers are necessary for presenting data to the user, but carefully selected combinations of data layers and supplemental cartographic information provide information to the user. Geographic Information Systems provide the tools for managing data and combining those data into informational displays that enhance the user’s understanding of the phenomena being examined. GIS Fundamentals 13 Elements of the GIS Process • Data Acquisition • Preprocessing • Data Management • Manipulation and Analysis • Product Generation GIS Fundamentals 14 Elements of the GIS Process Data acquisition is often the most expensive and time consuming part of any GIS project It may require: • Purchasing data from commercial vendors • Acquisition of data through field collection – Aerial photography – Satellite imagery – GPS – Ground survey – Manual digitizing, either with a digitizing tablet or on-screen • Download from government or other sources What types of data do you want to display? How are spatial data encoded into these data? GIS Fundamentals 15 Elements of the GIS Process Data preprocessing is required to modify obtained data for appropriate use in the GIS. This may include • Reprojection • Reformatting/Conversion • Subsetting • Checking for errors • Orthorectification What are the formats of the spatial data available to you? What coordinate systems are used for those data? GIS Fundamentals 16 Elements of the GIS Process Data management consists of a broad range of activities within the GIS that relate to the organization, processing, and storage of geospatial data. Activities included in data management include: • Importation of external data • Conversion from one data type to another within the GIS • Movement of data from one GIS workspace to another • Building topology • Reprojecting data • Joining attribute data with spatial data Do you have non-spatial data that you would like to map? If so, how might they be joined to available spatial data? GIS Fundamentals 17 Elements of the GIS Process Manipulation and analysis within the GIS might be seen to overlap with management, with the primary distinction being that manipulation and analysis results in: • New datasets based upon other datasets. For example: – Slope and aspect derived from a digital elevation model – The results of a model run that combines geospatial data and predefined processes – Reclassification of data into new representations of those data • Information about datasets as opposed to the datasets themselves (e.g. statistical information) What derived data do you want to generate? What types of statistical analyses do you need to perform? GIS Fundamentals 18 Elements of the GIS Process Product generation encompasses the set of activities that result in end products coming out of the GIS. These products include: • Hard copy maps • Digital representations of GIS data (e.g. TIFF, JPEG, GIF, and PNG files representing mapped data) • Tabular summary data derived from geospatial data or processes employed in the GIS (e.g. model output, or summary statistical data) • Exported geospatial data • Exported databases What information do you need to present in your maps? What standards does your organization use? GIS Fundamentals 19 Introduction to Linux 20 Introduction to Linux The GNU/Linux operating system and applications suite provide the foundation for the GRASS GIS application environment in the course. These tools consist of a robust collection of capabilities that must be understood to gain maximum benefit from the GIS environment. Areas to be discussed: • Logging in & setting a password • Interacting with the system • File system • Users and groups • Permissions • Installing Applications • Getting help Introduction to Linux 21 Logging In • Logging into the local system – Username & password: Generally, only the first 8 characters of the username and password are significant – Graphical login versus command prompt • Changing your password – Password best practices ∗ 8 Alphanumeric characters, mixed case ∗ Include punctuation marks ∗ NO: dictionary words, personal information, ∗ Change regularly • May be performed both from the command prompt and from a GUI interface • Login to a remote system – Telnet ∗ Commonly used to establish a connection to a remote system ∗ Insecure - username, password, and network traffic transfered in clear text – RSH ∗ Occasionally used to establish a remote connection. ∗ Insecure - username, password, and network traffic transferred in clear text – SSH ∗ Increasingly used for establishing connections to Introduction to Linux 22 Logging In remote systems. ∗ Secure - username, password, and network traffic exchanged in an encrypted mode. ∗ May be used for establishing a variety of connections, including: · Shell (ssh) · File Transfer Protocol (sftp) · File Copy (scp) · X-Windows Applications (ssh -X) ∗ It is good to get into a habit of using secure connections when possible Introduction to Linux 23 Logging In SSH Examples: ssh [-afgknqstvxACNTX1246] [-b bindAddress] [-c cipherSpec] [-e escapeChar] [-i identityFile] [-l loginName] [-m macSpec] [-o option] [-p port] [-F configfile] [-L port:host:hostport] [-R port:host:hostport] [-D port] hostname | user@hostname [command] • Connecting to a remote shell ssh -l kbene philostrate.unm.edu • Connecting to a remote system for interactive file trasfer sftp [email protected] • Transferring files from one system to another scp [email protected]:/home/kbene/testfile.txt [email protected]:/home/kbene/testfileNew.txt • Running X-windows applications on a remote system ssh -X -l kbene philostrate.unm.edu grass5 Introduction to Linux 24 Command Line vs. Graphical User Interface The execution of commands may often be accomplished via both the command prompt and via the system’s graphical user interface (GUI). Pros and Cons of GUIs • The GUI often provides access to complex functionality that would require