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Student Planetary Investigator (MESSENGER)
GIMP Mosaic Tutorial Creating Mercury Mosaics with Projected Images
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Student Planetary Investigator (MESSENGER)
Introduction You will be using projected images from USGS’s projection on the web (POW) service to create a mosaic of images of
Mercury’s surface. It is assumed that you have some experience with USGS’s PILOT image lookup service, and their POW
service. You will be guided through the process required to find images that are suitable for a mosaic, but are expected
to justify the section of Mercury that you choose to mosaic. By the end of this project, you should be able to discuss the
advantages of your high-resolution mosaic over the lower-resolution ones available on Quickmap.
NOTE: Because this tutorial utilizes the USGS/NASA PDS PILOT site, please complete the tutorial: “PDS
Tutorial: Using NASA’s Planetary Data System (PDS) to Find Mercury Pictures”.
Pre-Activity We will be using a free photo-editing tool called GIMP for this activity. You will need to check with your Network
Administrators to make sure you can download this software. Follow these instructions for download before you begin:
You can download GIMP here: http://www.gimp.org/downloads/ , or if that link has changed for some
reason, it is pretty easy to find with Google.
Go through the installation steps and start GIMP.
On startup, GIMP should have three panes and look similar to this:
Once you have installed and open GIMP, we will next look for images using the PILOT website.
http://www.gimp.org/downloads/
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Student Planetary Investigator (MESSENGER)
Part 1 This part will quickly review looking up images on the PILOT website http://pilot.wr.usgs.gov/ and discuss preparing
images for mosaicking.
Looking Up Images with PILOT:
Remember that the MESSENGER cameras will be more useful for our work, using mapped images.
Next, select the “Map” tab. Here you will see a map of the surface of Mercury.
In the lower left of the map, make sure the “bounding box” is selected.
This will allow you to create a box on the map to select a specific area for images. You can also input
long/lat coordinates to find your location.
Make sure your coordinate system is set correctly
Next, we will need to set the resolution for our area. Click on the “Advanced” tab next to the Map tab.
For a mosaic, you want as clear an image as possible. For my area, images with a mean ground resolution as
low as 100 meters / pixel were available.
When setting resolution settings in the “Advanced” tab, make sure to adjust settings for both the WAC and
NAC.
Remember that a lower m/pixel “mean ground resolution” translates into a high resolution image. It can be
a bit confusing because lower numbers yield greater pixel amounts.
http://pilot.wr.usgs.gov/
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Student Planetary Investigator (MESSENGER)
Start your search at higher mean ground resolution, and work your way down by steps until you have about
20 photos, as seen below.
Once you have about 20 images, use the view all footprints button to see the area that the images
encompass.
You could use one low-resolution image to see all the areas that these twenty images encompass, and
sometimes that is good enough, depending on what you want to do. But in this case, we want really good
images.
Now you have to decide if the area that you want to study is sufficiently covered. My images only cover the
center of my red box. If there is nothing on the right side of the box that I want to look at closely, this might
work for me.
But most of the time you will want to cover your entire region. Down below, I have lowered my resolution
and found footprints that cover my entire region.
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Student Planetary Investigator (MESSENGER)
However, 120 images are far more than you need. Remove all footprints, and then place footprints
individually using the globe icon next to each thumbnail. Make sure to place a checkmark at each image that
you place footprint.
As a reference, you can see the kind of information that is included in the individual frames:
Click here for more information
about the picture, camera, etc. If
you want to check your
resolution, click here.
This will download an IMG file,
which you don’t want right now.
This will place or
remove a footprint
of this image
If you want a picture of the image without
any projections, click this, then right click
“Save Image As…” when the larger image
appears. Usually saving as JPG or PNG is most
common and easily viewed.
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Student Planetary Investigator (MESSENGER)
NOTE: For this next part, you will need to be logged into the USGS site:
(https://astrocas.wr.usgs.gov/cas/login?service=http%3a%2f%2fastrocloud.wr.usgs.gov%2f).
When you press the download arrow, a window pops up:
When you hit the Go! button, you will see another window pop up:
When you hit the submit button, you will then be taken to the USGS
website and given a list of options for Map Projection on the Web Processing.
Submit your images, but make sure to keep your PILOT tab open.
At the USGS site, you will need to set some parameters for your image download.
Navigate to the image options tab. It is very important that
the output resolution of all your images are the same or
you can’t mosaic them together.
https://astrocas.wr.usgs.gov/cas/login?service=http%3a%2f%2fastrocloud.wr.usgs.gov%2f
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Student Planetary Investigator (MESSENGER)
Navigate back to the PILOT website
You want to find a good average resolution for all your images. Select the info button on one
of your images.
Look through the info pane until you find “mean
ground resolution.” (If you use the searcher tool
(Control + F), it should make it easier to find.)
Do this for several of your images, and take an
average. Set this average as your output
resolution. This means your higher resolution
images will be less clear, and your lower ones
will be slightly pixelated. However, pixilation
should be minor and not a problem. You can
always re-project your images later with a lower
resolution.
Now navigate back to the USGS site and type in
the average resolution you just calculated in the
Image Options window.
Select your projection settings as shown in the
PDS assignment. Output in a PNG.
Your images may take between 20 min and 24 hours to process. Once you have your processed images, proceed to
Part 2.
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Student Planetary Investigator (MESSENGER)
Part 2 For this part, you will use the GIMP photo-editing freeware to mosaic your images.
Once your images are finished, download the zip file, and extract it into a folder of your choice.
Open the GIMP program if you haven’t already done so.
Click FILE -> New
This should pop up a New Image window. I like starting with a 4000 by 3000 background because it gives me
a lot of room. You can start with a smaller background if you have a slow computer; it just makes the
mosaicking a little more cramped.
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Student Planetary Investigator (MESSENGER)
Next click FILE-> Open as Layers…
Use Control + Click to select all your PNG images and hit okay.
They will all be layered into a pile, so I like to spread them out for better visualization.
Use this tool to move images. If you are having trouble selecting
an image with the tool, switch to the “Move the active layer”
setting, and select the image in the layers panel.
If you think that your background layer won’t fit your entire mosaic, close your new file and create a bigger
background, then open as layers again. Be patient while it loads.
PUZZLE TIME! You may really enjoy puzzles and begin mosaicking from here. I like to have a bit of a
template. If you go back to your PILOT tab, you can look at the footprints again to get a general idea of
where the images go.
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Student Planetary Investigator (MESSENGER)
You can select an image to make the
footprint orange. Next, hold your mouse
over the thumbnail to get its name
(usually the last 4 letters are sufficient)
Go back to GIMP and drag the image with
that name into the general area of the
footprint. You can get it more exact in a
little bit.
You can use the “eye” button to hide
or reveal images while you are working.
Here I have quickly put my first 5 images in the correct location and hidden the other images. I have not yet
lined up any of the images to fit together.
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Student Planetary Investigator (MESSENGER)
Here I have put all my images in the generally correct position. It is still pretty easy to see that they don’t
line up very well.
Now it is time to start lining everything up. Hide all but two of your images.
I find that 50% opacity works best for me when I am lining up the images, so set it to 50% for now.
Select your two visible layers, and then use the opacity scroll bar above the layers panel. You can also
double click the bar, type in 50, and press
enter.
If you are working and find that 40%, 60%, etc. is nicer on your eyes, feel free to adjust.
Sometimes I like setting the back layer to 100%, and the front to 50%.
Remember that your images may have been taken under different angles/shadow conditions, and won’t line
up completely perfectly.
Tap your arrow keys repeatedly for fine movements. Tapping works better than holding the arrow keys,
since each new tap repositions the image. When you hold the arrow keys, the image doesn’t move until you
let go, and makes it harder to make fine adjustments.
Here are my first 2 images lined up. I returned them to full opacity when I finished. I can also drag my layers
in different orders to decide which is on top.
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Student Planetary Investigator (MESSENGER)
Notice that I used Control + Scroll Wheel to zoom closer to the above images (also accomplished with zoom
number at bottom of pane).
You may have noticed the alignment tool next to the move tool. I tried aligning images using this, and wasn’t
too impressed. I prefer to use the arrow keys. Feel free to try it out; you may like it more than I did.
The lineup won’t be perfect.
Always remember that shadow
conditions will make perfection
nearly impossible. Do the best
you can, but don’t spend ten
minutes trying to line up 2
images.
Now move onto the third image.
You may accidentally move one of
your 2 lined-up images while you
are adjusting the third. Don’t
scream in frustration and rip your
shirt. Use Control + Z or EDIT ->
UNDO to undo the adjustment.
Continue with an intact shirt.
Here are my first 8 images
mosaicked together. Notice how there are clear lines where some photos intersect. Hopefully you can limit
the visibility of these lines, but don’t worry too much about them.
If you notice that your mosaic
is too large for your
background, you may want to
make a larger background.
Just go to the layers panel on
the right, right click -> Add
New Layer…
Choose the size you need,
then delete the old
background layer with right
click -> Delete Layer
For this mosaic I started with
5000 by 4000 but it was a
little small for working with
all the photos.
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Student Planetary Investigator (MESSENGER)
You will also have to adjust the canvas size so click Image -> Canvas Size…
Set the canvas size to the same dimensions as your new background. You can also just select Fit Canvas to
Layers
A little more adjusting and the mosaic is now complete!
Now that everything is close and lined up, the large working background is just extra white space.
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Student Planetary Investigator (MESSENGER)
Crop out the extra space using the crop tool.
Just draw a box around the mosaic part and double click.
Now try comparing your mosaic with Quickmap.
Brian will write some cool science questions here.
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