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University of Nebraska–Lincoln


Purpose

In this activity, you will use a computer program that will take data and create a raster grid.


Background:

Raster grids are used to study a wide variety of images including those images that are created form satellite data. By making your own simple raster grids, you will see how satellite images, for example, are really composed of separate bits of data.

In an image, each piece of data has a measured value. For example, your data may be surface temperatures in a field. Your measured values may range from 55 F to 62 F. It is these values that are used to create the raster grid.


Materials:

    Macintosh Computer
    ClarisWorks Software (or other word processor)
    NIH Image Software

Procedure:

    1. Shown below is a simple overhead view of a region.

    2. Now a grid is overlaid on the region.










    3. To convert the data into values use the following numbers.

    0 = No water feature 1 = Water Body 2 = River

    0 0 0 0 0 0 0 1 1 1 0 0

    0 0 0 0 0 0 1 1 1 1 1 0

    0 0 0 0 0 0 0 1 1 1 0 0

    0 1 1 0 0 0 2 2 0 0 0 0

    0 1 1 2 2 2 0 0 0 0 0 0

    0 0 0 0 2 0 0 0 0 0 0 0

    Resulting Raster

    4. After the Claris Works word processing program has been loaded, type in the number values "in order, across each row", leaving a "space" between each number.

    5. Select "save as" from the ClarisWorks Window, pull down and select " Text." Now name your work and add ".txt". Quit ClarisWorks.

    6. Load NIH Image software. (See Teacher Notes: Opening NIH Image and Importing Values from ClarisWorks.)

    7. Once NIH Image has been loaded and your ClarisWorks text has been imported, click on the tiny icon found next to the heading "Tools." From the Options Menu, pull down and select "scale to fit window."

    8. Click and drag the lower right corner of the icon and pull the image to a larger screen size.

    9. At this point, read and answer questions 1 and 2 in the "Discussion" section of this activity.

    10. Color can be added to the raster gird you have on your screen.

    11.Select the "Options Menu" and pull down and select "Color Table." Look at the choices for color and select one.

    12. At this point, read and answer questions 3 and 4 in the "Discussion" section.

    Discussion: Copy and answer on you own paper.

    1. How many boxes does your raster grid contain?

    2. What does each of these boxes represent?

    3. What do the boxes of the same color have in common?

    4. How does adding color to your raster grid help you "see" the information better? Explain.

Extension

    1. Using the original hardcopy raster gridded map, have the students divide each of the pixels in half horizontally and vertically.
    2. Once the grid has been divided, have the students repeat the data entry procedure into ClarisWorks and NIH Image.
    3. When the image has been created, import the original image and make a comparison. The students should observe the different pixel size. This change in pixel size reflects a change in the resolution. Each new pixel now represents 1/4 the area each original pixel represented. The target details of the image have been greatly improved.
    4. Have students propose and discuss ways that increasing the resolution of an image affects the images quality.