-
Notifications
You must be signed in to change notification settings - Fork 1
User Guide Texture Files
LTVT, like VMA and most other Moon simulation programs, creates its images by copying the intensity at each latitude and longitude from a reference map. In the case of LTVT, for the rendering to make sense, the reference map must be in what is called a simple cylindrical projection. That is, longitude must be represented in equal pixel steps horizontally, and latitude in equal pixel steps vertically. The horizontal and vertical scales do not have to be equal, but for Textures 1 and 2 they do need to run from -180° at the left edge to +180° at the right edge, and +90° at the top edge to -90° at the bottom edge. Texture 3 is more flexible and can cover just a portion of the Moon (see Changing External File Associations for details), but it does have to be in simple cylindrical projection. Any map you can find that meets these criteria will be properly projected onto a sphere by LTVT. Windows bitmaps (.bmp), JPEG (.jpeg) and possibly other formats are supported. If you are not happy with the brightness, contrast or graininess of the image you are quite welcome to modify and re-save the reference map using any photo re-touching software (such as PhotoShop).
To make pleasing simulations, rather large reference files are needed. The distribution package includes only one texture file, called "lores.jpg". This is a reduced scale version of the very popular hand painted United States Geological Survey (USGS) shaded relief map produced on the basis of Lunar Orbiter images in the moon race days of the 1960's.
Like the "universal remote controls" sold for controlling TV/Cable/DVD, the program does not care what reference images you put under the three "radio buttons" that can be used for switching between textures. We find it convenient to have:
Texture1_Caption = Low Resolution Shaded Relief
Texture1_File = lores.jpg
Texture2_Caption = High Resolution Shaded Relief
Texture2_File = hires.jpg
Texture3_Caption = Clementine Photo Mosaic
Texture3_File = hires_clem.jpg
where lores.jpg, hires.jpg and hires_clem.jpg (or their *.bmp equivalents) are the default file names in the LTVT.ini file, but you can use whatever three reference files you like in whatever order you like. The files that are associated with the radio buttons, and even the captions next to them, can be modified with the Change external file associations... option under Files... in the LTVT main menu.
Step-by-step instructions for adding specific high resolution texture maps are given on a separate page. The following sections provide an overview of the options available.
If you have the Virtual Moon Atlas
Since most users of LTVT will have already tried VMA, the easiest way to obtain high resolution texture files is to "borrow" them from your VMA installation. One way to do this is to click Texture in the LTVT Main Window with either the High Resolution Shaded Relief (the Texture 2 default) or the Clementine Photo Mosaic (the Texture 3 default) radio button selected. LTVT will ask you to browse for the missing texture file. Simply go to the VMA textures folder, which is typically located at something like:
C:\Program Files\VirtualMoon\Textures\
and click on the appropriate file (you should find ones named the same way as the LTVT defaults: hires.jpg and hires_clem.jpg).
Another way is to use Change external file associations... under Files... in the LTVT main menu. In either case, when you are satisfied that everything is working, do a Save options.... LTVT will store the full path to this file in the LTVT.ini file for use on the next start-up. There is no need to physically move these files unless you want to. If you forget to Save options... you will be reminded about the change in file path when you exit LTVT, and given another chance to save the new one as the default.
If you do not have VMA, you may well want to download a copy. Not only will this supply usable texture files, but it is a very fine program in its own right, with many features not present in LTVT, such as telling you the dates of the various phases of the Moon, interesting information about lunar history and geology, and links to a database of high resolution photos.
The high resolution USGS Shaded Relief texture file is included with the "Expert" version of VMA. The VMA downloads page has an option for downloading and adding the high resolution Clementine photomosaic to the Textures folder. This is in the form of a *.exe file, which, when you execute it on your hard drive, will "install" the hires_clem.jpg file (you can actually do this without having the rest of VMA installed -- the Clementine image will be placed by itself in a newly created Textures file).
The other alternative is to download a custom reference map from one of the USGS Planetary Data Service (PDS) Map-A-Planet web-servers. See Texture Files Step-by-Step for further details. With this excellent and easy-to-use free service you can actually generate custom reference maps that not only show slightly greater detail than those provided with VMA, but also show a variety of different kinds of information. For example, you can generate color-shaded reference maps where the colors are related to the height of the lunar features or the composition of the surface materials. You can even download a map of another planet, such as Mars, and display it draped over a sphere (not completely accurate for Mars because of the different coordinate systems!) and viewed from different angles with LTVT, but that is another story...
Be warned that a high resolution image of the entire lunar surface is a large file. The hires.jpg texture map provided by VMA is a gray-scale image at a resolution of 32 pixels per degree (of lunar surface). As it comes with VMA it is 7.4 MB in size. If you request something comparable from Map-a-Planet it will be about 45 MB, because the download will be in "color" (even though that particular item is gray-scale). You can convert it back to a true gray-scale (about 15 MB) with any photo-processing software; but, as explained in the next section it is probably more desirable to convert it to bitmap format. A grayscale bitmap of this resolution will occupy about 64 MB on your hard drive, but it will load faster. Also note that the VMA shaded relief map is somewhat different from the PDS one (see the note about the archived relief map, at the bottom of this page).
For the very ambitious it is possible to download the raw USGS files on which the Map-a-Planet renderings are based, but it is much easier to let Map-a-Planet do the work. The files PDS uses are in a format something like the RAW files produced by high-end digital cameras, but cannot be read by most photo-processing software (again, see the example at the bottom of this page).
LTVT is reasonably flexible about file types, and should be able to create simulations based on reference maps in either JPEG (.jpg) or Windows Bitmap (.bmp) format.
Because LTVT renders only the number of pixels it needs to fill the viewing window on the screen, the time it takes to create the image is essentially independent of the zoom. It also seems to be nearly independent of the size of the reference file from which it retrieves the pixel intensities. However, because LTVT does not have the fancy filtering mechanisms of VMA, we find full disk images more pleasing if drawn with a low resolution textures, and high-zoom renderings of small areas with high resolution ones. The first time you request a particular texture, however, it does have to loaded from disk into the computer's memory. Large reference files do take longer to load initially, especially large JPEG files, which have to be decompressed into Windows native bitmap format in memory (sometimes you may see an indication of "Progress reading file" as the image loads, other times you will not -- this is not a defect of LTVT: some images provide this information, others do not).
If you wish to reduce the load time for the large texture files, it is desirable to convert the *.jpg files into *.bmp format. This is very easy to do with virtually any photo-editing software. Simply open the *.jpg file, and re-save it as a *.bmp. Although the files will be much larger on the disk (up to 64 MB each for the VMA high resolution JPEGS), they will actually load faster because the processor has less internal decompression/conversion to do. To make sure that LTVT recognizes and makes use of the *.bmp versions, you may wish to alter the default extension in the LTVT.ini file.
If you find LTVT hanging up, or your computer otherwise choking on these very large image files, you may wish to check you Virtual Memory preferences.
To do this, in Windows XP hold down the Windows key and tap Pause/Break. This will bring up the the System Properties panel. On the Advanced tab, click Settings in the Performance box. This will bring up a Performance Options panel. On this panel, again select the Advanced tab, and click the Change button in the Virtual memory box at the bottom. It is generally best to choose a System managed size for the Paging file, but select whatever you want and click Set. End with OK or Cancel. This may help, but it is not guaranteed.
An official archived version of the USGS shaded relief airbrush / simple cylindrical map of the Moon can be viewed, with an explanation of its scale, on this USGS page. It can downloaded, along with a "label" file, here.
This version appears to be the origin of the Shaded Relief map in VMA, in which the lunar mare (the naked eye "seas") are colored in a dark gray. It differs in subtle ways from the version delivered by the USGS's PDS Map-A-Planet. The latter shows the mare in the same light gray as the rest of the Moon, and includes a number of smaller features, especially in the polar regions.
Be warned that the desired file, sr_simp.img, found about a third of the way down the page, is a 64 MB download. The "label" file actually contains no information other than an explanation of the format of the image. And unfortunately this is a format which is "too simple" to be read by any of the normal Windows photo processing software: it consists of 5760 rows of bytes, each row containing 11520 bytes, and each byte representing a grayscale intensity between 0 and 255. Such Planetary Data System (PDS) images can be viewed with NASA's freely available NASAView software, but, to the best of our knowledge there is no mechanism provided (in that software) for converting it to a more widely accessible format.
Those who are really interested in this can request from us a simple but undocumented Windows program which will read the PDS grayscale *.img file and convert it into a huge (190 MB) Windows RGB bitmap. From there you can use any Windows photo processing program to convert it to an 8-bit grayscale Windows bitmap (64 MB). Either of these latter formats are usable by LTVT. You may also wish to slightly alter the original by blurring/sharpening or changing the contrast and brightness. But as noted above, after all that effort, the results will be only marginally better than the hires.jpg file provided with VMA. You can produce a better map much more easily with Map-a-Planet.
LTVT also has the capability of creating simulations based on any Earth-based photo or other image of the Moon that has been calibrated by the LTVT user. The calibration enables LTVT to associate each intensity point in the image with a precise selenographic longitude and latitude. Hence the intensities in the image can be used as a reference map for creating lunar simulations, although there will naturally be regions of the Moon over which no intensity information is available. When such a photo is used as the reference map, these no-data areas are (by default) represented by a light blue color in the simulation. You are free to change this color under Tools...Change Cartographic Options...
Please note that Earth-based photos are not in a simple cylindrical projection, and hence cannot be substituted for any of the three main texture files. Indeed, LTVT assumes that an Earth-based photo is in what is called an orthographic projection appropriate for the date, time and observer location at which the image was recorded. Using such a file in place of one of the normal simple cylindrical reference maps will produce grossly inaccurate results.
A simple cylindrical Earth texture is needed for using the Earth viewed from Moon feature. There are many sources of such images on the internet. The most prolific source is the NASA Visible Earth website, where many of the Earth textures can be found in the "Blue Marble" collection. The sample texture provided in the full download is Land Surface, Shallow = Water, and Shaded Topography.