Pixel Transmission Activity

Overview:  Students will work in groups to develop code systems to transmit information between groups.   Groups are given a problem; they have to use a long strip of paper to transmit a map to another group.  They are only allowed to write 1s and 0s on their strip, no punctuation or spacing is allowed.  The  pairs of groups   meet in advance to decide how their code system will work.   Then they are separated to encode their maps.  Then they exchange codes with the other group and try to draw the map from the code.  They may need to meet again to discuss how the code works but eventually they should get so they can translate a code into a map.  This should be followed by a teacher led discussion of satellite sensors collecting data and streaming it to earth where it must be organized and translated into images.   This activity will help students understand resolution and pixels.  The activity can then be extended then by adding color coded maps and more numbers (with a possible discussion of binary coding) which can allow analogies to multispectral data and using different LUTs.

Topics:

Scientific Visualization:  2D Area Rendering

NC Scientific and Technical Visualization Objectives:

   Level II  3.01 B.  The student will identify sources of data and applications for 2-D area rendering.

NC  Earth and Environmental Science Goals and Objectives (objectives from 1994 revision):

   5.2    Demonstrate knowledge of current research in earth/environmental science.
   6.1    Demonstrate knowledge of mapping skills and location of points on earth.

Materials
pencils, graph paper, colored pencils, long strips of paper

Teacher Instructions

Students will solve the problem of  devising a coding scheme suitable for  encoding and transmitting map data.  They will have to work together to discover and agree on a code and transmission protocol that will work.  Do not give the students a transmission protocol.  They will develop a need for it as they try to solve their transmission problem.  They will have to agree on at least the following:   whether 0 or 1 codes for land,  the exact width and length of their map, which corner and which direction they will start with.  It is best to have the first map students work with be small and simple.  The 1st picture below  is a sample simplified island map, suitable for the first iteration.   The coding scheme is  illustrated in the second box.  A one was used when  a box had any land at all, otherwise a zero was used.  On a long strip if we start in the upper left and move across this would appear as

0000000000000111000000111100000111110000011111110001111111100111111110011111111000001110000000000000

The third box illustrates the result.  In order to decode the long strip correctly a group would need to know that the map was 10 by 10, the code starts in the upper left  and moves left to right, and that 1 coded for land.
 

Rather than explaining to students how to do this activity, try allowing them to figure it out.   It will help them to have materials and sample maps while they discuss their coding schemes. If the students are stuck there are several ways the problem can be made easier. In the first iteration, they can use graph paper instead of the long strips  to transmit the numbers - then all they have to decide on is whether ones or zeros are shaded.  The first maps passed out can also be stylized designs (like the result on the right above) so that students aren't confused by attempting  to transmit information about darkness of shading or information about which part of a box is shaded.  The problem can be made easier by giving all groups small graph paper squares that are cut out to be exactly the same size or harder by giving them larger sheets of different sizes.  The first maps can be teacher produced, but students will enjoy producing their own.  Given a State map different groups can be assigned to produce an encoded  map of a particular county or island or Outer Bank island.   The other group will then have to decode the map and  figure out which county (out of a limited number of possibilities)  or island the map represents.

Discussion

After completing this activity the teacher should ask how the map coding would be affected by using graph paper with smaller squares - if each small square was divided into 4 smaller squares or 9 smaller squares.  This leads to the concept of a pixel  and the relation of pixels to image resolution.  A pixel is a picture element of an image.  If you keep zooming  in on an image in an image processing program you eventually see that the image is made up of many tiny boxes -each with one color.  Each box is a pixel.  In this example each graph paper square represents one pixel.  If students are not already  familiar with this have them try zooming in on an image using  your image processing software.    Just as the students had to choose whether boxes that were partially shaded should be coded with ones or zeros,  a satellite sends an average value for each area it samples.  The smaller the sampling area for a pixel, the higher the resolution of the image.

Then ask the students to transmit maps with color coding of different types of  features.  (For example dark green for forest, yellow for sand,  light green for grazing land, red for grain crops etc)  Now they will have to agree on a more complicated coding scheme.   The groups receiving the maps might choose to use different colors to represent the data they receive. This is like changing the LUT, it doesn't change the underlying data that was transmitted only the display which can be manipulated to emphasize the features of interst.    Depending on the mathematical sophistication of the class you may want to explain that since digital transmission is only of ones and zeros all other numbers must be converted to binary before transmission.    Ask students to discuss how true color, false color, and puedo color images would differ in this process.  Remember in true color images the image uses  red, blue, and green light to represent the red, blue, and green light recorded by the sattelite sensors.  False color uses red blue and green to display information from other usually not visible light parts of the spectrum and psuedo color uses color to represent different values of one measured quantity such as temperature.  So a  map that uses color for altitude would be psuedo colored.

Other concepts which can be discussed here include:  scale and different error checking schemes (checksum).  For example the map can appear larger but not convey any more detail if there are the same number of larger squares on the output map.  Regardless of the size of the output map the scale is determined by the size of the squares that each pixel represents.
 

Step by Step

1. Prepare graph paper squares with simplified maps  in advance
2. Put students in an even number of groups of 2 or 3 students.
3. Pair the groups.
4. Pass out an example map and strips of paper to each group.
5. Explain the problem.  Tell students that each group will be given a map.  They will have to transmit the contents of the map to their partner group using only the long sheets of paper and 1s and 0s.  No punctuation or grouping symbols allowed.  They can meet in advance to decide on their coding sheme and transmission protocol.
6. Have group pairs separate.
7. Give each group a map to transmit and a paper strip.  Have them exchange strips when ready.
8. Each group should then decode the strip they received into a map.
9. Groups should compare their maps to the originals.
10. Follow discussion outlined above.

References
This activity was adapted for use of Scientific Visualization classes from the  "No Class is an Island" and "Gaia Challenge" Activities from The Gaia Crossroads Project Guidebook to Using Satellite Imagery In the Classroom and Community.   This guidebook is an excellent source of information about using remote sensing images in the classroom.    The "No Class is an Island"  activity was originally developed by Larry Ryan for Maine Center For Education Project SEED and the "Gaia Challenge" activity  was created by Dean Meggison at  Kennebunk High School in Maine.  For more information check out the Gaia Crossroads Project website at  http://www.bigelow.org/~gaia/

last update 4/6/99