Lunar Terminator Visualization Tool (LTVT)
A freeware program that displays a wide range of lunar imagery and permits a variety of highly accurate measurements on these images.
- This software is freely available from the LTVT Wiki.
- Works only on Windows-compatible computers.
- Displays simulated orthographic (distant) lunar view from any selected observing location.
- Lighting conditions and viewing geometry for Earth-based observations can be automatically computed from the JPL ephemeris or manually entered.
- Nomenclature search/overlay directly tied to IAU Planetary Gazetteer. Additional name/location information can be easily added.
- Only one low-resolution texture is provided, however the user is free to add any number of global textures (including the many freely available from Map-A-Planet; and a wide variety of maps and images (both from Earth and satellites, including the user's own lunar images) can be displayed in the same projection.
- Fixed size viewing window, but unlimited capability to zoom in on surface detail, and possibility of running any number of simultaneous instances of the program to overall and compare images.
- A uniform set of analysis tools is available for all images, including the ability to measure distances, angles, sizes, sun angle, and interpret shadow lengths in terms of height differentials.
Some of the images displayed in this Wiki were created from Lunar Orbiter photographs using LTVT. In most of the these cases, the three sub-frames of the original high resolution LO photos were pasted back together to re-create the original continuous strip. A small section of that strip was then re-mapped to a north up aerial (overhead) view with LTVT. LTVT images always represent orthographic views showing what the lunar surface would look like as seen in projection from a great distance. The legends at the top and bottom of its images indicate which original frames were used, and the position and scale of the image being displayed. The LTVT "zoom" factor indicates how many similarly-sized frames would be required to encompass the full lunar diameter. For example, if the image width is 641 pixels and the zoom is stated as "20", this means it would take 20x641 pixels to completely cover the projected lunar diameter of approximately 2x1738 km.
In other cases, the sizes and heights of features have been estimated using images "calibrated" with LTVT. Calibration consists of informing LTVT of the date, time and location from which the photo was taken, and allowing LTVT to make the spatial adjustments necessary to bring the observed positions of lunar features into conformity with those expected from a Unified Lunar Control Network.
LTVT height estimates are based on shadow lengths and always represent the difference in radial elevation (distance from the Moon's center) between the starting and ending points of the shadow.