New Media in Landscape Architecture: Advanced GIS

Transcription

1 New Media in Landscape Architecture: Advanced GIS - Projections and Transformations - Version 10.2, English ANHALT UNIVERSITY OF APPLIED SCIENCES Hochschule Anhalt Author: Dr. Matthias Pietsch Tutorial-Version: 2015

2 Exercise Projections and Transformations In many cases all the data in a given project is based on a single coordinate system. Therefore the question about which coordinate system is involved slips into the background. But because of the increasing amount of available data and the possibility to collect datasets using Global satellite navigation systems (GNNS) like GPS or GLONASS implemented e.g. in smartphones sometimes requires to manage different coordinate systems in one project. On the other hand the globalization of data exchange (Internet, WebGIS) indicates that the user has to take an active part in deciding how to handle inhomogeneous data and that he or she do this with a qualitative understanding of how coordinate systems work. There are different possibilities to project and transform datasets (vector and raster) in one specific reference system using ArcGIS. Therefore a lot of reference systems (Geographic Coordinate Systems and Projected Coordinate Systems) are predefined. To enable ArcGIS to overlay different layers using on-the-fly projections for each layer the specific coordinate system must be defined. Task: Project dataset from different coordinate systems (geographic and projected coordinate systems) in a single one. Data: - landuse (vg_kcir) Shape-Format - topmap 1: (georeferenced) (12cb2hs.tif) Tif-Format - coordinates (dbf.dbf) dbase Table (collected using GNNS) Used function: - Define Data Frame Properties - Display XY Data - Export datasets - Project Features How to do this 1. Prepare your dataframe Windows Data Frame Properties Start ArcMap and create a new Map Document. To define the Coordinate System for the Data Frame rightklick on the Data Frame and choose Properties. Select the Tap Coordinate System inside the Data Frame Properties window. No Coordinate System is defined yet. 2/8

3 Adding the first layer with an existing predefined coordinate system, this will be used as the standard coordinate system for the existing Map Document. Close the Data Frame Properties. 2. Add XY-data It s possible to create point features based on existing coordinates e.g. from GNNS devices. But it s necessary to know the reference system of the existing coordinates to be able to define the specific coordinate system. Standard toolbar Tool Add Data Add the coordinates from the GNNS device using the existing dbase-table from the folder \tables. The coordinates in the table are represented in geographic coordinates (WGS 84). 3/7

4 Display XY Data Rightclick on the table and open the Display XY Data menu. Select the field LAT as X-Field and Long as Y-Field. Define the Coordinate System of the Input Coordinates using the Edit button. Select the predefined Geographic Coordinate System WGS1984.prj for the point features (Event-Layer). Create an Event-Layer by clicking OK twice. Now you have created an Event-Layer that represents the position of the coordinates. To create a permanent layer that can be used for visualization and further analysis you should convert the Event- Layer e.g. into a Shapefile. 4/8

5 3. Create a Shapefile TOC dbf Events Righclick on the Event-layer dbf Events and open the Export Data window. Select this layer s source data as coordinate system and export to the Output feature class point.shp. 4. Project Datasets Because we defined WGS1984 as the reference system of the Event-layer the Shapefile has the same coordinate system. To visualize the created point features with the other existing datasets it s necessary to project the coordinates from the geographic coordinate system in a predefined projected coordinate system. Therefore you can use ArcCatalog or the ArcToolbox. The following example explains how to use the ArcToolbox. Standard Toolbar Arc Toolbox Open the Arc Toolbox window by clicking on the Arc Toolbox symbol inside the Standard Toolbar. Window Arc Toolbox Data Management Tools Projections and Open the Tool Project by doubleclick. Click the folder symbol next to the Input Dataset of Feature Class window and browse to \shape\point.shp. By selecting the point layer the Input Coordinate System will be added automatically. Transformations Feature Project 5/7

6 Define the Output Feature Class \shape\point_gk.shp. Output Coordinate System Spatial Reference Properties Select To define the new Output Coordinate System open the Spatial Reference Properties by clicking the button next to the Output Coordinate System window. Browse inside the Spatial Reference Properties window to the Projected Coordinate Systems\National Grids\Germany and select Germany Zone 4.prj. Add the coordinate system as the spatial reference and close the Spatial Reference Properties window by clicking OK. If necessary choose the first entry out of the drop down list next to the Geographic Transformation (optional) window and start the Project Tool by clicking OK. Make sure that the list beneath Geographical Transformation (optional) contains only one entry, otherwise the Project tool will malfunction. 6/8

7 Standard Toolbar Add Data If necessary add the result by clicking Add Data inside the Standard Toolbar. To check the coordinate system of a specific layer open the Layer Properties window with rightclick on the layer name. Select the Source Tab. There you can check the defined coordinate system is described. 5. Define the same reference system for all existing datasets (raster and vector) and visualize them in a new ArcMap document Create a new Document. Standard Toolbar Add Data Add the layer \shape\point.shp and check the coordinate system (layer properties). Add the layer \shape\vg_kcir.shp. The Spatial Reference for that data source is missing. 7/7

8 Click OK to add the layer. ArcToolbox Data Management Tools Projections and Transformations Feature Define Projection To define the missing coordinate system for the shapefile you can use the Define Projection Tool. Open the tool with doubleclick. Select vg_kcir as Input Dataset. Coordinate system Spatial Reference Properties You can define the coordinate system by selecting the specific Projected Coordinate System like you have done before. If you have an existing layer with a predefined coordinate system you can select in the dropdownlist beneath Layers. Select Germay_Zone_4. Click OK and define the projection with OK. Standard Toolbar Add Data Add the layer \tk\12cb2hs.tif. Don t create pyramids and ignore the message Unknown Spatial Reference. Define the projection in the same way like you have done for the vector layer. 8/8