China

China’s data is probably the easiest to get output from, but its main issue is the reliability of the website serving the data. I would recommend anyone serious about studying China’s data to spend a few days downloading all the files they have available - it doesn’t take too long, all you have to do I fathom out their website.

There are three sets of data to play with, two from their first orbital probe Chang’e-1 and one from the second one, Chang’e-2. I’ll refer to these as CE1 and CE2 respectively for ease of writing.

China’s lunar map is divided into labelled sections (see below). CE1’s files are much smaller and have a lower resolution, but they are useful ones to have as a way of checking which file you need to look at in the more detailed dataset. The second set of data is an accompanying DEM (Digital Elevation Model) file collection that can help build surface models. At the time of writing this is not available.

China’s site has recently updated, and at the moment the individual tiles aren’t readily available (at least in an easy to find format), but it does say that it is ‘coming soon’.

Each rar file contains a TIF image, a ‘.03’ file, and a ‘.tfw’ file. The tfw file is a one that contains simple information about a photograph’s location. The .03 file can be used in the same software that opens the CE2 data. For most things, the TIF image is just fine here and it can be opened in any image viewing software.

The Chang’e-2 data files are larger, and contain files that can only be read with specialist software such as NASAView or, if you own a copy, in Photoshop.  You can find NASAView via this page, and you’ll need to supply an email address to get the download link.

Photoshop users can pretty much skip lots of the following, as there is a simple way of opening the .03 files using built in features. This document describes the process for files in ‘.IMG’ format from the Lunar Reconnaissance Orbiter, but it also works for China’s .03 format.

First, instead of going to ‘File’, ‘Open’, go to ‘File’, ‘Open As’. From the ‘Open As’ list choose ‘Photoshop RAW’.

What isn’t immediately obvious is that the images are divided into 3 parts, and so far you’ve only opened on of them. If you were sure you’d captured the right part of the image you could just save it now, but if you do that it seems to stop it from letting you open the other parts of the picture. So, my recommended procedure is to go straight to the ‘Large Image Selection’ menu and go to the ‘Next Line Samples’. Do this twice and you’ll have all three elements of the image open.

All you need to do now is to save these sub-windows as three separate images by going to ‘File’, and choose the image format of your choice. I tend to go for ‘Save JPEG As’. You then have three high quality images that you can explore to your heart’s content. You can even merge them back into one image using (for example) Photoshop.

If you have a GIS package like QGIS (discussed on the JAXA page here), you can load the .03 file in there by dragging it into the layers panel.

This allows you to browse over the whole image, and also to export it as an image file in the format of your choice.

QGIS allows the export of just the area shown in the frame, so you can zoom in and get a more detailed image export.

At the time of writing the individual tiles for China’s elevation model aren’t available, but after I emailed them they sent me a temporary link to the global DEM - the entire surface of the moon in one 400Mb file! It looks to me as though the individual tiles of the CE1 data are just this large map split into chunks, so we do have something to work with.

The only slight snag is the projection of the map - the global DEM and the photographic data are using different projections, so getting the two to work together is more difficult. I spent many happy hours trying to match the two coordinate systems without success, so in the end I resorted to a process known as ‘georectification’ or ‘georeferencing - forcing the photographic and elevation to match using common features on both. It won’t be an exact match but given the resolution of the layers it will be good enough?

So, how does this work? The first step is, as usual, to load the DEM and photographic layers into your GIS package, and as with other probe data I‘ll be using QGIS. Here’s the view with the DEM and the CE2 tile covering Hadley Rille loaded.

It’s difficult to tell, but the actual location of the photographic tile should be some distance north-west of its current position. What we need to do now is find some common reference points on both layers so that we can force them to sit on top of each other in the right place. To do this we need to use QGIS’s georeferencing feature, which can be found under the ‘Raster’, ‘Georeferencer’ menu, or by using the ‘hatched’ looking shortcut on the toolbar:

Next, click on the left-most icon (the chessboard looking one with the plus sign) to add the raster you want to move - ie, the one you’ve added on top of the DEM. Once it’s loaded it will look like the window below right.

Hopefully you can see above the role the different map projections play in things - on the map the CE2 tile is flat and square, whereas in the Georeferencer window it is correctly displayed relative to the curve of the moon’s surface. Next you need to get in close to the areas you want to match up. As there is a slight overlap in the two images it helps to turn off the CE2 tile.

The easiest features to look for are craters, as they stand out on both maps, whereas a change in elevation marking a bright mountain feature could be too subtle to identify accurately. Georeferencing in QGIS needs a minimum of four co-referenced features but the more the merrier. It also helps if the features are closer to the area you’re interested in as it increases the accuracy of the re-plotting of the photographic layer around the specific spot you want to look at.

The next step is to tell the Georeferencer that you want to add a point, which is done by clicking the ‘add point’ icon:

The other two icons there are ‘Delete point’ if you get one wrong (just click that icon then click on the point you want to get rid of), and then ‘Move point’ if you get one in the wrong place. My method here is to click on the exact centre of the crater I want to use as a reference. In the image below I’ve zoomed right in on a crater I’ve identified as being in both layers. Clicking first in the georeferencer window you’ll get another box pop up asking for coordinates of the point on the main map. If you actually know them then great, by all means type them in but it’s much easier just to click on the ‘From map canvas’ button and click on the equivalent point in the main GIS window. Note you can move from window to window and zoom in and out using the scroll wheel on your mouse.

As you move onto the main window, the From map coordinates box will disappear, and it will reappear once you’ve clicked on it with the coordinates of the point you’ve added filled in in both the box and below the georeferencer window. I should point out that to save space the image above is a composite showing all parts of the process - you won’t see the red dots until you’ve clicked ‘OK’ on the From map coordinates box.

Repeat this process as many times as you can to get the most accurate transformation.

Once you’ve got your minimum of four points, you need to click on the ‘cog’ icon to tell it how you want to do the georeferencing. You’ll get the following:

Again this is a composite window showing everything you need. By default the ‘Create world file’ tick box may be selected - you need to untick that so that it will actually create a new map layer that it will add when it’s done. You need to tell it where that map layer is and what it will be called by clicking the three dots at the end of the ‘Output raster’ line. You can just accept the default it gives you or specify your own.

You also need to choose the ‘Target SRS’ to match the one on the map. If you forget this you can still select it in the main program when you’re done.

Click on OK when you’re happy. The final step is to click the big green triangle ‘Start Georeferencing’ icon.

You’ll see a couple of windows appear telling you it’s working, then some ‘OK’ buttons to click when it’s done. With any luck if you selected your referencing points accurately you should see an accurately plotted photographic layer appear. When you close the Georeferencer you’ll see messages about keeping or discarding the reference points you added - you can safely discard them if it’s all worked.

What you can also do is try and generate a 3D view using the Chinese data - see the page on Japanese data I referenced above for how that works.

It should be obvious what the different resolution has done to the detail in the map - it is much less accurate and detailed than the higher resolution Japanese and Indian DEM models.

If you want to have a go at the Apollo sites yourself, I have uploaded the Global DEM and CE1 and CE2 files to a Dropbox account. The links are given below. The values in brackets are the map subdivisions on China’s map if they ever come up again:

Global DEM

Apollo 11 CE1 (G012)

Apollo 11 CE2 (G012)

Apollo 12 CE1 (H009)

Apollo 12 CE2 (H009)

Apollo 14 CE1 (H010)

Apollo 14 CE2 (H010)

Apollo 15 CE1 (F011)

Apollo 15 CE2 (F011)

Apollo 16 CE1 (H011)

Apollo 16 CE2 (H011)

Apollo 17 CE1 (F012)

Apollo 17 CE2 (F012)


Have fun exploring China’s space data!

It will now read the file and open it as it would any other iamge. Job done, and you can play around to your heart’s content!

This method will work for CE1 and CE2 .03 files.

If you don’t have Photoshop, you’ll need to use NASAView. Go to the file menu and select ‘Open Object’. Browse to the directory containing the file and select it. You’ll see a window like this:

You’ll get a dialogue box with image details in. You can just accept what it comes up with and hit ‘OK’.

Apollo Overview 3D Overview