Didger 4: Projection and Datum Tips NewsletterHome

Didger is a complete georeferencing package with a suite of tools for calibrating and correcting the coordinates of images and data. When georeferencing in Didger, there are some simple steps you can take to avoid common challenges, and increase your efficiency. This article explains the following items: Coordinate systems generally have specific projection, projection settings, and datum. The exception is Geographic coordinates (latitude and longitude), which are not considered projected. Three commonly used coordinate systems are: Latitude and Longitude, Universal Transverse Mercator (UTM), and State Plane Coordinate System (SPCS). The projection defines the numeric coordinate system. The datum defines a reference ellipsoid used to compensate for the curvature of the Earth. Knowing which projection and datum apply to your source images or data files is very important. Changes in projection or datum can result in maps not overlaying properly in other programs, so knowing which projection and datum you need when you export from Didger is equally important. A common Didger question is “Where did my map go?” If you import data and the plot goes blank or the plot stretches dramatically in the X or Y direction, the coordinate system for at least one of the files may have been misidentified. Try re-importing the data with a different coordinate system. Often you may not know what the projection system or datum are when you receive the data file. You can usually make an educated guess by first examining the coordinates. If the data is an Excel spreadsheet or a CSV file, you can open the data in Excel, view the data, note the coordinates, and close the file. If the data is in a text data file, you can open it in a text editor, like Notepad, or you can open it in Didger. To open and view the coordinates in Didger, follow these steps: What a tremendous progress Golden Software made over the last 20 years. I am delighted to use the latest tools. Dr. Istvan Almasi P. Geol. Thanks for your promptness...but not surprising considering the great service I have gotten in past years. Mindy Brugman Revelstoke BC I very much like working with Golden Software. I find the software very easy to use and very helpful.David Orr, Shrimp Biologist, Fisheries and Oceans Canada Copyright © 2016 Golden Software, LLC. All rights reserved. The names and logos for Surfer, Grapher, Voxler, MapViewer, Didger, Strater and Golden Software are registered trademarks of Golden Software, LLC. Source.

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