User's Guide

(Updated March 8, 2008)

Input Map Images

When you first start G.Projector, you are presented with a file dialog asking you to select a source input map. The image formats you can open include BMP, GIF, JPG, and PNG and on some platforms TIFF. But what other constraints are there on your choice?

First, you don't have to select an input map at this time. You could click the cancel button in the file dialog and just work on a map projection which shows only continental outlines. Or you could later "import" an input map in the projection you are working with.

But if you do decide at this time to apply an input map, then (1) it must be in equirectangular form, (2) it must be centered on the prime meridian (0° E/W), and (3) it must have no border or margin.

The G.Projector distribution includes a folder called "sample_maps" which holds three equirectangular map images: two of Earth and one of Mars. Please note that it is best to avoid using source map images which are overly large because memory problems may ensue. The "world_topo_bathy_200407.jpg" image included in G.Projector is 1800 pixels by 900 pixels and works well, but much larger images (e.g., the NASA Blue Marble downloads which are 5400×2700 pixels) can cause G.Projector performance to bog down and perhaps even hang.

Map Windows

After that first open-file dialog, G.Projector will display a window showing the map, with a lower panel holding several controls to manipulate the map projection and appearance.

The first line of controls affect the map projection. First is a menu which lists the 80+ projections currently available. Next is a text field for inputting at which longitude the map should be centered, and for some projections a text field for the latitude at which it should be centered Most of projections in G.Projector cannot be centered off the equator, so in those cases the latitude field are not shown. That value and the input field are used by azimuthal projections such as the Orthographic.

Several of the projections also have an extra parameter. When one of those projections is chosen in the menu, an additional text input field or a checkbox will be appended to the line of controls. For example, the Equirectangular has a parameter called "Standard Parallel". This is the latitude at which east-west distances are correctly rendered.

The second line of plot controls includes controls for choosing how the lines of the longitude-latitude grid should be drawn, if they are drawn at all.

The third line of plot controls allows you to specify what lines should be drawn overlaying the map, if any. Probably these will be outlines of the continent edges. When you first start working with G.Projector, it will offer you six choices of Earth continent outlines, the difference being the amount of detail. One of these outline choices is built into the G.Projector application, but you will find that the other five correspond to files located in the "overlays" folder in the G.Projector distribution. Any CNO type overlay files located in this folder will be automatically added to the menu or overlay choices when G.Projector is started.

Importing Image and Overlay Files

After a map window has been opened, it is still possible to apply a different source equirectangular map image than your initial choice. To do so, select the "Import Map..." item in the File menu or type command-D (Mac) or control-D (Windows and Linux).

You can also use CNO overlay files located elsewhere on your hard drive than in the standard overlays folder. Select "Import Overlay..." from the File menu, or else type command-shift-D (Mac) or control-shift-D (Windows/Linux).

Additional overlay files compatible with G.Projector are available on the Panoply software website. Select only the CNO "outline" files there, and not the masks.

Removing an Imported Image

If you have placed an imported equirectangular image in your map and decide you want to remove but not replace it, use the "Remove Import Map Image" item in the Edit menu, or type command-shift-X (Mac) or control-shift-X (Windows/Linux).

Click Options

When viewing a map, there are two special mouse click options you can use:

An "alt-click", i.e., clicking while also holding down the "alt" or "option" key, on the map projection will cause a little box to be displayed which displays the longitude and latitude of where you clicked. This box remains visible until you click on the map again.

A "shift-click" anywhere on the map will cause the map to be re-centered where you clicked. Note: Only azimuthal projections are truly re-centered at that point. Non-azimuthal projections are instead centered on the longitude of the click point.

Contact

If you questions about G.Projector which are not answered above, please contact the author:

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