Preferences

Upon start the user is presented with Mirone in its basic form which is a simple bar with menus only. Activities are initiated by using those menus. Although Mirone comes with pre-defined defaults it is very important that the user understand what they mean and do. The first time the program is used the user is strongly advised to hit the button with hammers icon. That opens the preferences window. The meanings of those settings are as follow:

The grid/image type of coordinates. Select Geographic (default) if you are working with a grid whose coordinates are longitude and latitude. Select Cartesian otherwise. This is an important setting because some operations, like measuring, depend on knowing if we are dealing with geographic or Cartesian coordinates. When a grid is read, Mirone tries to guess what coordinates it has and although it guesses correctly most of times, it may fail.

· Grid Max size - In order to do all grid manipulations Mirone stores the original grid in the computers memory (regardless of their type they are always stored as single precision). This is the maximum size in Mb that a grid can have and be held on the computer's memory. This does not mean that larger grids/images cannot be processed. It only means that if they are larger than this value, they will be re-read from disk whenever necessity demands. It is up to you (based of course on the computer capabilities) to decide on a reasonable value for this parameter. Grid size is computed in the following way: n_rows x n_columns x 4 / (1024*1024). Note: Mirone does most of its heavy computation with external MEX files that use single precision arithmetic's. However, some operations may still be done with MATLAB operators which imply double precision (in this case it takes twice as much memory). When you are using image files, however, this rule does not apply anymore. In fact there is no obvious rule because you may be using compressed or uncompressed images.

· Swath ratio - When doing a multibeam planning one always has to know the swath width coverage as a function of the water depth. When you start the first track, a question will be made if you accept this value or want to change it. Subsequent tracks won't ask it again, so if you want to change it in the middle of a planning session, you have to come here.

· Measure unites - When computing distances that's the result is presented in the chosen unit. Available options are: nautical miles, kilometers, meters and user (it means I don't know what are these).

· Default ellipsoid - Mirone computes distances on an ellipsoidal Earth. Among the various ellipsoids you will also find one for Mars. Do not forget to select this when working with MOLA grids. Besides the default ellipsoids an alternative mechanism is provided to supply different ellipsoids via an external file. In the data subdirectory there is one example file named ellipsoids_example.txt that shows how such a file should be written. To make this file active, rename it to ellipsoids.txt and it will than take precedence over the built-in default ellipsoids.

· Working directory - To reduce the cumbersome task of browsing trough the directory tree every time you need to save a file, the program uses a default working directory. You may either write the full path here or press the side button and select one within the selecting window that will open. Besides this mechanism, the program also remembers the last directory used to open a file and will use it as a first guess for the next time you need to open another file.

· Scale geog images at mean lat - Since 1 degree of longitude and latitude do not cover the same arc length at Earth surface, isometric plotting of geographical grids squeezes the image vertically. Scaling the Ys axis to the cosine of the mean lat minimizes this effect. However, if the image has a large latitudinal extent the image will have a nearly one-to-one relation at the center but will show an important distortion at top and bottom.

· Force insitu transposition - This is an option to help importing large grids. Importing grids implies a conversion that uses matrix transposition. This operation is fast if we make a copy of the importing grid. However, this requires twice the grid size on memory. If you do not have enough memory to import a large grid, use this option that does the transposition insitu. That is, it uses only one time the grid size in memory. The price to pay, however, is in speed because it runs about 10 times slower.

· Move lines with a left-click - Controls what mouse selection is used to move polylines/patches. If checked lines are moved with a left click drag-n-drop. Though easier to operate this has often annoying side effects (move the polyline when in fact we wanted to edit one of its vertexes). Uncheck if you want to use a Shift-click left mouse button or click both left and right mouse buttons to move the line. A bit more cumbersome, but safer.

· Default line thickness - Use this default value for drawing lines, circles or other graphical elements.

· Default line color - Use this default value for drawing lines, circles or other graphical elements (such as text strings).

On the second tab Fledermaus one selects the behavior when creating Fledermaus objects by clicking one eye icon of the Mirone bar. As mentioned in Save as Fledermaus object, we can choose between planar or spherical objects (useful to visualize global grids). The other options under How to deal with vectors control if line elements are transferred as vectors, in which case they have an altitude attribute that allows them to intersect the surface, of if they are rasterized into the image.

Copyright <2010>, <Joaquim Luis>

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