SO432, GIS Fall 2009

Datums, Map Projections, and MGRS Lab

This lab will be individual effort.  You will answer the following questions with a typed, paragraph answer.  You might wish to attach copies of printouts to support your answers, and calculate specific results.  This is a writing requirement, and the quality of your answers are important.  Writing that directly includes the questions is worth a C grade.  It will be due Tues, 2 September,  and will be turned in in paper format at at the start of the period.  You can also submit an electronic version if you want to insure that color graphics are visible.

1. Which of the projections in MICRODEM are conformal, and why do we care about this property?
2. How "bad" is the distortion of the Mercator projection, and when can you live with it?  Support your answer with graphics and a table.
3. Which of the planar projections (stereographic, orthographic, Lambert azimuth equal area) works best for animations of the earth's rotation?  Why is this?
4. What is the difference between the UTM and Mercator projections?  How does the pattern of distortion vary between the two projections?  Support your answer with two maps, one in each projection, and discuss the differences.
5. Why must the military worry about datum shifts, and does it really make a difference?  Support your answer with a table for Korea, Afghanistan, and training in the US, and discuss how both UTM and lat/long coordinates shift.  You should also have a map to show this.

The questions below will not be turned in, but should help you to answer the questions.

References

1. Help file for the MICRODEM program; pages linked from "Cartography" on the opening screen.

2. Reference: Chapter 3 in DEFENSE MAPPING AGENCY, TECHNICAL MANUAL 8358.1 DATUMS, ELLIPSOIDS, GRIDS, AND GRID REFERENCE SYSTEMS.  Online at

• http://164.214.2.59/GandG/pubs.html
• http://www.usna.edu/Users/oceano/pguth/website/so432web/e-text/DMA_8358_1a.pdf

Using MICRODEM

Use the MICRODEM program to answer the following questions.  You can download the program and install it on the computer in your room from http://www.usna.edu/Users/oceano/pguth/website/microdemdown.htm .

• Load maps with the File, Open Vector Map  menu choice.  Pick as many projections as you would like if you set the check box to allow multiple maps.

• Use the Cartography menu choices to look at the distortion on the map.

  • The “map distortion” menu choice will show h, k, and omega at the bottom of the screen, and print the values on the map if you double click.
  • The “Tissot Indicatrix” option will plot indicatrices on the map.
  • The “datum shift” menu choice will show the difference between the two datums as you roam. 

Cylindrical projections.  We have the following cylindrical projections:

• Mercator
• Equidistant  cylindrical
• Miller cylindrical
• Cylindrical equal area

What is the common feature of each of these projections?  How does the pattern of distortion vary among them?

Planar projections.  We have the following planar projections:

• Stereographic
• Orthographic
• Lambert azimuthal equal area

Are any of these conformal?  How does the pattern of distortion vary among them? Make a movie (Cartography, Earth Rotation menu choice) with each of these projections.  Which is the best, and which is the worst?  Why?

Conical projections.  We have the following planar projections:

• Conic equal area
• Lambert conformal conic

Are either of these conformal?  How does the pattern of distortion vary between them?  How hard is it to tell the difference between these two projections?

Mercator Projection.  Distortion pattern on the Mercator projection.  You might loose the outlines of the countries and states; if this happens you can bring them back by taking off the smart 

Blow up the map to show the United States.  How much scale difference is there on the map (give the range of latitude/longitude, and the differences in h/k)?

Blow up the map to show the Chesapeake Bay.  How much scale difference is there on the map (give the range of latitude/longitude, and the differences in h/k)?

Blow up the map to show the Naval Academy region.  (Note that the coastline is not very good at this scale, and may even disappear.)  How much scale difference is there on the map (give the range of latitude/longitude, and the differences in h/k)?

If you are willing to accept 5% distance scaling errors (in which case areas will be off by 1.05*1.05), how large a region can you display on a Mercator map?  What part of the earth is best depicted on this projection?

Stereographic Projection.  Distortion pattern on the stereographic projection.

Get a polar, oblique, and equatorial aspect.  What parameters must you vary to get these different aspects?

Plot Tissot indicatrices on the polar and equatorial aspects.  What is the pattern of distortion on each?

If you are willing to accept 5% distance scaling errors, how large a region can you display on a stereographic projection?  What part of the earth is best depicted on this projection?  Consider the polar and equatorial aspects separately.

Datum shifts: insure that you have the correct datums selected, using the Options menu choice, Maps tab.  Then use the Cartography, Datum Shift menu choice.

• In Korea, how big is the difference between WGS84 and Tokyo Datum coordinates?
• In Europe, how big is the difference between WGS84 and European 1950 (mean) coordinates?
• In Afghanistan, how big is the difference between WGS84 and Indian (Pakistan) coordinates?
• In the US, how big is the difference between the NAD27 and WGS84 datums?