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Calibration of NIH Image
- First, you are going to measure the diameter of the hurricane.
To do this you must obtain an estimate of the average pixel size along
the measuring line.
- Select the line segment icon in the Tools Window and draw a segment
between the tip of the Yucatan Peninsula and Washington, DC on the image.
This distance is 1329 miles. {to get hints on how to determine this
distance, go to Resources-"step
by step"}
DISTANCE DETERMINATION
- Start Netscape Navigator
- Open How far is it? (You
should bookmark this site)
- Click on Xerox PARC Map Server (a map of the earth appears)
- Click on the tip of the Yucatan Penninsula.
- Zoom in by clicking until you can clearly see the tip of the pennisula.
(As you zoom in closer and closer, the image will take longer to appear.)
Above the image you will find the latitude and longitude of the location
you clicked on.
- Highlight the latitude and longitude then go to the menu bar and choose
Edit-copy.
- Go to the menu bar and choose Go-How far is it? (You should be back
to the How far is it? site).
- Place the cursor in the From box and click the mouse button.
- Go to the menu bar and choose Edit-paste. (You should see the latitude
and longitude of the spot you chose on the Yucatan).
- Click Xerox PARC Map Server again. (The image of the world map appears
again.)
- Click on a place near Washington D.C. (Don't worry about being exact,
you only need to be close to this location.)
- Zoom in by clicking until you are satisfied you are near Washington
D.C. (As you zoom in closer and closer, the image will take longer to appear.)
Above the image you will find the longitude and latitude of the location
you clicked on.
- Highlight the latitude and longitude, and then choose Edit-copy.
- Go to your new bookmark and choose How
far is it?
- Place the cursor in the From box and click the mouse button.
Paste latitude and longitude.
- Go back to How far is it?
Choose the second point on the map. Highlight the latitude and longitude
and then choose Edit-copy for the second point. Place the cursor in the
to box and click the mouse button and paste lattitude and longitude.
- Now click on the button titled Look it up!
- You are now at a new page where the distance is given in a straight
line between the two points both in miles and in kilometers.
- First, you need to use this distance to set the scale in NIH Image.
- Second, in NIH Image, pull down the Analyze menu and select Set Scale.
Select miles as your unit of length. Enter the Known Distance of 1329 miles.
- Third, measure the diameter of the hurricane. Use the line tool
to draw a segment of the desired length and location (across the middle
of the storm). Pull down the Analyze menu and select Measure,
then Show Results. A box should appear in the upper left side of
the screen with the distance given in miles.
- Fourth, find the diameter of the area affected by the hurricane, not
just the central part of the storm. (Use the procedure in third step
above)
- Fifth, select the freehand tool in the
Tools Window and circle the strongest part of the hurricane (the whitest
part of the image). Go to Options on the menu bar and select Area (make
sure Perimeter/Length is also selected).
- Answer the following:
- What is the perimeter of that part of the storm?
- The area?
- How does this area compate to the area of the state in which you live?
- Perform the same sort of analyses on images
Finally, as the hurricane crossed from water onto the land, what happened
to its shape?
