Visualization of Gravity Field Models of Celestial Bodies (Moon, Venus, Mars)

This is an interactive Java Applet to visualize the Gravity. You have many options to load other models, change grid resolution, viewpoint, zoom, light source parameters ...
You must enable Java for your browser to use it.

Netscape 6.xx, Mozilla, MS Internet Explorer are recommended browsers. Older versions of Netscape will work, but much slower, because they do not have installed a JIT-compiler.
If you don't see it correctly on your browser, please inform us per Email (include the used browser version and operating system).

Please have some seconds patience for loading the applet. See below the applet for usage info.

Usage

Most buttons (or the button-labels) have a help option: if you move the mouse cursor over it, a small popup will explain its function.
The Earth can be rotated either with mouse cursor dragging (sometimes a bit slow) or the keyboard actions (see below).

Button panel

• You can select 3 different Bodies for display with the top left button: Moon (of Earth), Venus and Mars. Displayed is always the model with highest resolution.
• You can switch between Geoid (more exactly "Moono-id",...) and Gravity Anomaly
• zoom [+], [-] With these two button you can zoom and unzoom your region of interest. Before you do this, move it into the center of view, as described below.
• boost Sets the 'exaggeration factor' i.e. 'hboost = 10000' means that 1m of geoid undulation is displayed as 10km high mountain.
• grid Sets the grid resolution. The smaller this value, the more details become visible, but also the slower will be the display. Depending on your OS-/Browser-/Java-version such very fine resolutions may require your configuration actions to supply sufficient Java heap space, see Troubleshooting below. See Performance tips for speed considerations.
• smooth Toggles between two display modes. If it is 'off' you will see the discretizing triangles of the grid, else the colors inside the triangles are interpolated.
• back Toogles between two views of the body: default only front-view, else front- and back-view.
• rotate With this toggle button you can let the Earth rotate around its polar-axis.
• Light Pops up a new window to set some light control variables (position, focus parameter 'gamma').
• new Frame Pops up a new window with the same Applet. This has the additional feature, to be resizable (with your usual window-manager handles). With this window you can also compare two models or views, or make screen shots from it. Both frames are controlled independly, but the memory usage adds up, of course.

Keyboard actions

Please note, that the Applet must have the focus for keyboard actions!

• The arrow keys (left, right, up, down) can be used to move the earth.
• Pressing the up- and down- arrow-keys while holding "Ctrl", will change the colormap scale-factor (always by a factor of 2). This is especially useful, if you inspect model differences which have usually small amplitudes.
• The +,- or <, > keys can be used for zooming/unzooming. (Some browsers seem to ignore these keys sometimes, however the +/- keys on the numeric keypad should always work)
• The p-key toggles display of plate-boundaries.
• There are some other keys (s,o,c,h,b) to select other background images.

Performance tips

If you want to experiment with certain display variables (as light, model, lmax, zoom, viewpoint, ...) it is probably the best way, to first use a small grid-resolution (2° or 4°).
Also 'rotating' and interactive motions will work more fluently with lower resolutions. After finding out the best display, you can set the resolution to the desired value. Doubling the grid size will produce a nearly four times increased update time (and memory requirements).
To use very fine resolutions < 0.5°, you should close all other browser pages, to have the maximum available Java heap space (e.g. a grid resolution of 0.2° needs about 540 Mb memory).

Troubleshooting

If you experience some odd behaviour of your applet (no reaction to buttons, no image updating, ...) you can inspect what is going wrong, if you have a look at the Java Console of your browser. For Netscape 6.xx you open it with the buttons Tasks → Tools → Java Console. There the main actions and errors are logged and you have the possibility to control the Java Virtual Machine (JVM).

One common error, which freezes the applet is the "OutOfMemoryError". It occurs if the pre-allocated heap memory for your JVM is exhausted, usually already in the step "generating sphere points". This can happen for grids < 0.5°, because some older browsers only allocate 64Mb for Java. (You can see the error message in the Java Console window of your browser.) You can circumvent this failure e.g for Windows-PCs, if you change the default value in the browser preferences under "Java" → "runtime environment" → "runtime parameter -Xmx500m" to allocate eg. 500Mb heap space.
If you see only a blue sphere in the window but no geoid, then there is a network/server problem (eg. your local firewall blocks the connection). Please inform us about this, we try to help.

Technical notes

The Applet is loaded from the server host "icgem.gfz-potsdam.de" with "Potato.jar". It requires a running potato-server listening on TCP-port 1891. After start of the applet, it queries from the server the list of available models, which build up the model choice of the applet. Then it serves model queries in form of grid values.
The applet needs quite a lot of memory, depending on grid-resolution. In the default resolution of 1° × 1° it occupies approximately 16 Mb, resolution and about 60 Mb for 0.5° × 0.5°.