The WSC Data Users Guide

Transcription

1 Page 1 of 8 Mekong River Commission Secretariat GIS - Applications for Watershed Classification The WSC Data Users Guide Prepared by the Centre for Development and Environment (CDE), University of Berne, Switzerland July 1997 CONTENTS i List of Figures 3 ii List of Tables 5 iii List of Abbreviations & Keywords 7 iii List of Commands 9 iv Foreword 13 v Introduction 15 Part I Introduction and Background 17 1 What is Watershed Classification? Introduction The WSC map and its applications 21 2 What is GIS? Computer basics to get started The GIS software Introduction to PC Arc/Info and PC SEM 27 3 The WSC data The data delivered with the manual 29

2 Page 2 of The data delivered by MRC and other data 32 Part II The WSC Data 35 4 How to use the WSC data Displaying the data on PC Arcedit Getting information on coverage features Modifying the existing coverage features Adding new features to a coverage Creating a correct topology 45 5 The digital terrain model (DTM) on PC SEM What is a DTM? Building a DTM with PC SEM Generating a slope map 53 Part Ill Combination of data 59 6 Combination of data - producing a WSC map Elements of the WSC map Combining the WSC parameters A map composition for the WSC map 67 Annex 69 A SML Example 71 B Information for Idrisi Users 43 I List of Figures Figure 2.1 Extract of a WSC map converted into a graphic 26 Figure 2.2 Elements of a vector file 26 Figure 4.1 Reshaping of an arc (elevation contour) 42 Figure 5.1 DTM building with the TIN algorithm 48 Figure 5.2 Building a DTM and further calculations with PC SEM 49 Figure 6.1 Transformation of a grid image into a polygon coverage 62 II List of Tables Table 3.1 Files contained in arcda.exe, disk 1 (for PC Arc/Info users) 29 Table 3.2 Files contained in idrdat.exe, disk 2 (for Idrisi users) 30

3 Page 3 of 8 Table 3.3 Naming of coverages 31 Table 3.4 File format of the WSCP data 32 Table 5.1 Slope value classification 54 Table 5.2 Example of slope value classification 55 Table 5.3 Suggestion for a LUT using the shadeset plotter. shd 56 Table 6.1 The WSC class limits 64 Table 6.2 Item values of wsc. lut 66 Table 6.3 RGB - colours used for the original WSC maps 67 Table 6.4 Transformation of the WSC colours into percentile numbers 67 III List of Abbreviations & Keywords AAT Arc Attribute Table. A Algorithm Arc/Info A set of rules which specify a sequence of actions to be taken to solve a problem. Each action is precisely and unambiguously defined so that in principle it can be per-formed by machine GIS software. The PC version of this software is used for demonstration in this manual. The UNIX version of it was used to create the WSCP data. Back coverage Coverage used for display purposes but not activated for editing operations B Back environment Feature(s) of the back coverage to be drawn Area from which water runs off to any given river valley or collecting reservoir. Catchment Area from which water runs off to any given river valley or collecting reservoir C CDE Cells Contours Co-ordinates Centre for Development and Environment (Institute of Geography, University of Berne / Switzerland). Smallest map units with homogeneous information (also called Pixels). Lines at the same elevation above sea level. Systems of numerical indications used for georeferencing locations on maps and/or in the field. Digitalisation Transformation of an analogue file into a digital file. D DOS DTM DTM errors GIS Disc Operating System. Operating System used on PC workstations Digital Terrain Model (equivalent to DEM = Digital Elevation Model). Computer stored map containing topographic information (elevation) over the entire map surface. The quality of a DTM depends on the quality of the input data (contours, points, etc.). Incorrect information in the input data produces wrong DTM features. Frequent types of input data errors are: wrong contour elevation, inter-section of contours with different elevations, mismatches between points and contours or between rivers and contours, double digitalisation of contours Abbreviation for Geographic Information System: Data base of spatial information G

4 Page 4 of 8 GIS software Grid Interpolation Data base management system to store and process spatial information. A computerised representation of a raster file. Calculation of elevation values for the entire map surface from given contours and/or points, using an algorithm. I Label Coverage element (point), also for polygon definition L Lineset Arc/Info file defining the size, pattern and colour of the linear features of a coverage or map composition. MRC Mekong River Commission Secretariat in Bangkok / Thailand. M PAT Polygon Attribute Table or Point Attribute Table P PC Projection Personal Computer System of mathematical formulas used to transform geo-graphical information from one map to another or from the physical world to a map. Raster Division of a (digital) map into the smallest map units with uniform/homogeneous information (cells). The size of raster cells is userdefined (resolution). R Resolution Resource River basin Size of the cells in a raster map or a raster-based DTM as a function of the map or DTM scale. A component of the natural environment used in order to meet particular human needs. The act of exploitation converts the component into a resource Large river systems composed of numerous catchments and sub-catchments. SDC Swiss Agency for Development and Cooperation S Spline TIN Topography UNIX Watershed Workstation WSC WSCP ARC/INFO function (algorithm) for interpolation. Constructs surface trends in order to calculate a continuous surface using given contour/point elevation. Triangulated irregular Network. Algorithm for calculating the smallest possible triangles between known elevation points (on contours and/or points). These triangles are the smallest map unit. The TIN algorithm produces a discontinuous surface. Description of the surface features of a particular landscape. Operating System. The UNIX Arc/lnfo version runs on this Operating System, while the PC Arc/Info version runs on the DOS Operating System Dividing line between two catchments. Used in practice as a synonym for catchment. In our context: UNIX based workstations (as opposed to DOS based PC workstations). Watershed Classification: classification of a landscape into different watershed classes, as a description of the potential topographic soil erosion risks to the landscape based on its physical and/or environmental features. Watershed Classification Project for the Lower Mekong Basin started in June 1990, and co-ordinated by the Mekong River Commission Secretariat T U W IV List of Commands

5 Page 5 of 8 Command Software Description &run Arc modules Starting a SML macro. Add Arcedit Adding edit features to an edit coverage. Tables Adding entries to the items of an attribute Additem Tables Adding an item to an attribute table. (AAT / PAT) or a lookup table (LUT). Altitude SEM Selecting the vertical viewing angle (observer s position) for a three-dimensional view. Arcedit Arc Accessing the Amplot module Arcidris Idrisi Importing a Generate file to Idrisi. Arcplot Arc Accessing the Arcedit module Arcs Arcplot Drawing the arcs of a coverage into a map composition. Arcsem SEM Transforming a PC Arc/Info coverage into a SEM (Structured Elevation Model). Aselect Arcedit Selecting an additional set of edit features while preserving the first selection. Tables Selecting all items of an attribute table. Azimuth SEM Selecting the horizontal viewing angle for a three dimensional view. Back Arcedit Choosing a back coverage, i.e. a coverage which is drawn on the graphic device, but which can t be edited. Backe Arcedit Choosing the back environment, i.e. those features of the back coverage to be drawn onto the graphic device. Build Arc Calculating a correct topology for a coverage (options = polygon / line / point). Calculate Tables Calculating items or item entries of an attribute table using logical expressions. Clean Arc Calculating a correct topology for a coverage (options = dangle length and fuzzy tolerance). Color rgb Arcplot Redefining the colour-index for the current Arcplot session. Coordinate Arcedit Choosing the digitising device (coordinate digi to choose the digitiser). Define Tables Creating a new attribute or lookup table. Describe Arc Describing the general characteristics of a coverage. Idrisi Showing the characteristics of a raster file. Display Arc/lnfo Definition of the display device used in Arcedit and Arcplot. Display 4 defines the monitor as graphic display. Idrisi Deploying a spatial data on the monitor. Dissolve Arc Joining together polygons having the same value for one or several of their items. Distance Arceditv Showing the distance between 2 points

6 Page 6 of 8 SEM Selecting the viewing distance to a three-dimensional view. Document Idrisi Documenting spatial data. Draw Arcedit Drawing the edit coverage and the back coverage onto the graphic device. Drawe Arcedit Choosing the draw environment, i.e. the features of the editcoverage to be drawn on the graphic device after using the draw command. Drawselect Arcedit Drawing the selected features with the chosen draw symbol (Sds). Drawsem SEM Displaying a SEM - plotfile (three dimensional view, drape) onto the graphic device. Editcoverage Arcedit Choosing the edit coverage, i.e. the coverage to be edited (manipulated). Editfeature Arcedit Choosing the feature (arc, polygon, label, annotation, tics) to be edited (manipulated). Only one at the time. Erdidris Idrisi Importing an erdas file (raster) into Idrisi. Gridascii Idrisi Importing raster files into Idrisi. Import Arc/Info Importing data into PC Arc/Info. Idrisi Importing data into Idrisi. Initial Idrisi lnitialising a new raster file. Intercon Idrisi Computing a DTM Items Tables Listing the items of an attribute table. Labelerrors Arc Getting information on the label errors of a coverage. Linecolor Arcplot Attributing a colour symbol to a line feature. Lineras Idrisi Transforming a vector file into a raster file List Tables Listing the entries of an attribute table Map Arcplot Naming and initiating a map composition. Mape Arcplot Setting the extent of a map composition. Arcedit Zooming in a coverage. Mkdir DOS DOS command to create a new directory. Move Arcedit Moving one or several edit features. Nodeerrors Arc Getting information on the node errors of a coverage. Ortho Idrisi Computing and displaying a three dimensional view. Polygonshade Arcplot Drawing a polygon coverage with different shades / colours, depending on the reference item, the selected shadeset and the selected lookup table (LUT). Q stop Tables Exiting Tables while saving changes made in the current session. Removeback Arcedit Removing the back coverage. Renode Arc Updating the arc-node topology of a coverage.

7 Page 7 of 8 Reselect Tables Selecting an item or specific entries of an attribute table. Reshape Arcedit Redrawing an arc. Resolut SEM Defining the resolution of a three dimensional view. Save Arcedit Saving an edit coverage. SEM Saving a plot file as an Arc/Info coverage. Select Arcedit Selecting one edit feature. Tables Selecting an attribute table. Select many Arcedit Selecting several edit features. Select Sid =... Arcedit Selecting all edit features having a common identity. Sds Arcedit (= Setdrawsymbol) Choosing the symbol (colour) with which selected features are drawn. Semarc SEM Saving a DTM as an Arc/Info polygon coverage. Shadeset Arcplot Selecting a shadeset for the polygonshade operation. Surface Idrisi Calculating different surface options (aspect, analytical hillshading, etc.) Tables Arc Accessing the Tables module. Undelete all Arcedit Undoing edit changes. Union Arc Computing the geometric intersection of two polygon coverages. View3d SEM Generating a three-dimensional view of a DTM. Window Idrisi Creating a new raster file using an extract from an existing raster file. Zfactor SEM Defining the vertical exaggeration of a three-dimensional view. FOREWORD Planning for natural resources is a complex multidisciplinary task. It typically involves the generation, storage, processing and integration of large amounts of spatial information. The Watershed Classification Project which was designed to provide an analytical tool for land use planning and watershed management in the Lower Mekong Basin was challenged by this condition from the very beginning. In its early stages the Project relied on more conventional technologies for data generation and processing. However, soon it turned out that these technologies could not live up to the requirements of an advanced planning instrument in particular in terms of analytical capability, flexibility and versatility. While searching for technologies meeting these requirements, the Project selected the Geographical Information System (GIS) as the obvious choice. After careful consideration the project was redesigned for GIS application. Geographical Information System is a recent and still very dynamic technology. Most professionals of the riparian countries involved in natural resource management have not been exposed to training in this field during their formal studies. The present WSC Data Users Guide intends to compensate to some extent for this shortcoming by providing the background and skills required to generate, process and store digital data for watershed classification. As the term Guide indicates, it is a hands-on reference for staff directly involved in watershed classification activities. It complements the WSC Map Users. Guide, which addresses the methodological aspects of the Project, with technical information and practical instructions. I am confident that the present Guide is well suited to promote the skilful and responsible application of Watershed Classification in the Lower Mekong Basin.

8 Page 8 of 8 Berthold Schrempp Senior Watershed Management/Forestry Officer