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Marine Data Literacy 2.0

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Home > 2. Marine GIS > 2.4 Graticules & Frames > 2.4.1 Frames Check

2.4.1 Accuracy Check for AOI Frames

New Version of Saga:  Usually a new version of Saga is quickly assimilated into these exercises.  The latest release, Version 2.1.2, is so radically different that it will take some time to catch up with revised exercises.  Please email me immediately whenever you find an old exercise that simply cannot be accomplished in the new Saga, due to big changes in the properties, etc.  I will try to provide fixes within about 2 days.

  • Exercise Title:  Accuracy Check for Area of Interest (AOI) Frames

  • Author:  Murray Brown

  • Version:  February 2013

1.  This check is the most important of all, because you use the graticule shape and the lines shape frame for other checks.
2.  Load the following shapes into Saga:
  • World Borders map (a polygon shape)
  • Area of interest graticule (a lines shape)
  • Area of interest frame (a lines shape)
  • Area of interest frame (a polygon shape)
3.  Use ADD TO MAP to plot the World Borders data and then plot the graticule on top of it.  The graticule should appear in exactly the place where you want it to be.
4.  Make a map of the graticule.  Enlarge it, and carefully check the X, Y coordinates of all 4 corners.  They must be exactly as expected, but a very tiny error much smaller than the grid cell size is OK.  [This is due to cursor movement precision.]

NOTE:  The coordinates are displayed along the bottom line of the Saga window.

5.  Plot the lines frame on top of the graticule (preferably in a different color).  They must match exactly.
6.  Plot the lines frame or the graticule on top of the polygon frame.  They must match exactly.
7.  You absolutely MUST get these accuracy checks right, because most other checks and data products depend on frames for location, spatial resolution and size.  Don't go forward until you are sure you have accurate frames.