MGRS lab

SO432, GIS Fall 2006 Draft

MGRS

You may work on this lab in groups of 2. 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. It will be due Wed, Sept 7, and can be turned in in paper format or electronically.

What is the difference between MGRS and UTM coordinates?

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

Reference: Chapter 3 in DEFENSE MAPPING AGENCY, TECHNICAL MANUAL 8358.1 DATUMS, ELLIPSOIDS, GRIDS, AND GRID REFERENCE SYSTEMSOnline at

Mercator Projection. Distortion pattern on the Mercator projection.

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 Cheaspeake 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.) How much scale difference is there on the map 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?

MGRS consists of three parts:

· Grid zone designation, 2-3 characters (1-2 numbers and 1 letter)

· 100,000 m square letter identification (2 letters)

· Grid or rectangular coordinates (2-10 numbers, even number)

Setting up MICRODEM to display the datum shift:

· Select options from the menu, and pick the following:

1. Maps tab, set the primary (WGS84) and secondary datums (NAD27 or other as desired).

2. Default UTM zone 11

3. Coordinates tab, set “Both datums when roaming” and “MGRS and Lat/Long while roaming”.

4. Pick the menu choice "Cartography, Datum shift" and double click at points on the map.

MGRS:

On the cartography menu choice, you can:

1. Overlay the MGRS grid zones. They will be outlined, and named if the scale allows.

2. Overlay the 100,000 m squares and label if the scale allows. Colors will alternate in the different zones.

You should overlay these on two types of projections:

1. Mercator ellipsoidal

2. UTM ellipsoidal. After changing to this projection, you may want to use the following variations (be careful how you change, and this projection is not forgiving of a poor choice of parameters; you must pick a UTM zone that is on the map):

The defaults as initially set.

Change the width to 4000 km, and the NW corner to 51N, 125W

· Change the width to 12000 km, and the NW corner to 50N, 130W

MGRS:

1. What are the rules for the first three characters of an MGRS?

Size of the zones:
Letters used, and pattern:
Numbers used, and pattern:
Where are the zones that do not follow the normal pattern? (If you need help, look on NATO’s northern flank.) Why do you think this was done?

2. What are the rules for the two letter 100,000 m square IDs?

Letters used:
Which letter is used for northing, which easting?
How far must you go N-S to find a repeating letter?
How far must you go E-W to find a repeating letter?
Why do letters appear to skipped as you move E-W?

3. How many 100,000 m squares are there in each zone? Does this vary, and if so, if which direction(s), and why?

4. How does the shape of the zones, and 100,000 m squares, appear on the two projections (Mercator and UTM)? Are they the same everywhere on the two projections? What does this say about the properties of the two projections?

5. How will the MGRS coordinates meet at the edge of two zones, and what happens if you continue the coordinates from one zone into the next? Will this effect be greatest at low or high latitudes?

6. Look at the 100,000 grid squares for the Annapolis region, with maps on both NAD27 and WGS84. Why would the MGRS system be constructed this way?

7. What is the difference between MGRS and UTM coordinates around Annapolis?

8. Can you see the patterns of map distortion in the 100,000 m squares?