gimp mosaic tutorial - shasta union high school...

Student Planetary Investigator (MESSENGER)

GIMP Mosaic Tutorial Creating Mercury Mosaics with Projected Images


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/


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/


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.


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.


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


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.


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.


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.


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.


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.


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.


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.


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.

gimp mosaic tutorial - shasta union high school...

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