mapinfo_mif.txt

mif文件格式-,Visual C++,文件格式/File Formats

106 Zanderij Surinam International 
Units 
The following table lists the available coordinate units and the number used to identify the 
unit in the MAPINFOW.PRJ file: 
Number Units 
6 Centimeters 
31 Chains 
3 Feet (also called International Feet)* 
2 Inches 
1 Kilometers 

Chapter 2: Creating Your Own Coordinate System 
Number Units 
30 Links 
7 Meters 
0 Miles 
5 Millimeters 
9 Nautical Miles** 
32 Rods 
8 US Survey Feet (used for 1927 State 
Plane)*** 
4 Yards 
* One International Foot equals exactly 30.48 cm. 
** One Nautical Mile equals exactly 1852 meters. 
*** One US Survey Foot equals exactly 12/39.37 meters, or approximately 30.48006 cm. 
Coordinate System Origin 
The origin is the point specified in longitude and latitude from which all coordinates are 
referenced. It is chosen to optimize the accuracy of a particular coordinate system. As we 
move north from the origin, Y increases. X increases as we move east. These coordinate values 
are generally called northings and eastings. 
For the Transverse Mercator projection the origin’s longitude defines the central meridian. In 
constructing the Transverse Mercator projection a cylinder is positioned tangent to the earth. 
The central meridian is the line of tangency. The scale of the projected map is true along the 
central meridian. 
In creating a Hotine Oblique Mercator projection it is necessary to specify a great circle that is 
not the equator nor a meridian. MapInfo does this by specifying one point on the ellipsoid and 
an azimuth from that point. That point is the origin of the coordinate system. 
Standard Parallels (Conic Projections) 
In conic projections a cone is passed through the earth intersecting it along two parallels of 
latitude. These are the standard parallels. One is to the north and one is to the south of the 
projection zone. To use a single standard parallel specify that latitude twice. Both are 
expressed in degrees of latitude. 

Chapter 2: Creating Your Own Coordinate System 
Oblique Azimuth (Hotine Oblique Mercator) 
When specifying a great circle (Hotine Oblique Mercator) using a point and an azimuth (arc), 
the azimuth is called the Oblique Azimuth and is expressed in degrees. 
Scale Factor (Transverse Mercator) 
A scale factor is applied to cylindrical coordinates to average scale error over the central area 
of the map while reducing the error along the east and west boundaries. The scale factor has 
the effect of recessing the cylinder into the earth so that it has two lines of intersection. Scale is 
true along these lines of intersection. 
You may see the scale factor expressed as a ratio, such as 1:25000. In this case it is generally 
called the scale reduction. The relationship between scale factor and scale reduction is: 
scale factor = 1–scale reduction 
In this case the scale factor would be 1–(1/25000) or 0.99996. 
False Northings and False Eastings 
Calculating coordinates is easier if negative numbers aren’t involved. To eliminate this 
problem in calculating State Plane and Universal Transverse Mercator coordinates, it is 
common to add measurement offsets to the northings and eastings. These offsets are called 
False Northings and False Eastings. They are expressed in coordinate units, not degrees. (The 
coordinate units are specified by the Units parameter.) 
Range (Azimuthal Projections) 
The range specifies, in degrees, how much of the earth you are seeing. The range can be 
between 1 and 180. When you specify 90, you see a hemisphere. When you specify 180 you see 
the whole earth, though much of it is very distorted. 
Polyconic Projection 
The following description is copied from “Map Projections -- A Working Manual”, USGS 
Professional Paper 1395, by John P. Snyder. 
The Polyconic projection, usually called the American Polyconic in Europe, achieved its name 
because the curvature of the circular arc for each parallel on the map is the same as it would be 
following the unrolling of a cone which had been wrapped around the globe tangent to the 
particular parallel of latitude, with the parallel traced onto the cone. Thus, there are many 
(”poly-”) cones involved, rather than the single cone of each regular conic projection. 

Chapter 2: Creating Your Own Coordinate System 
The Polyconic projection is neither equal–area nor conformal. Along the central meridian, 
however, it is both distortion free and true to scale. Each parallel is true to scale, but the 
meridians are lengthened by various amounts to cross each parallel at the correct position 
along the parallel, so that no parallel is standard in the sense of having conformality (or 
correct angles), except at the central meridian. Near the central meridian, distortion is 
extremely small. 
Editing the MAPINFOW.PRJ File 
The MAPINFOW.PRJ file lists the parameters for each coordinate system on a separate line, as 
in the following examples: 
“Mollweide (Equal Area)”, 13, 62, 7, 0
“Albers Equal–Area Conic (Alaska)”, 9, 63, 7, –154, 50, 55, 65, 0, 0
“Alabama,Western Zone (1983)”, 8, 74, 7,–87.5, 30.0, 0.9999333333, 600000, 0
“UTM Zone 9 (NAD 27 for Canada)”, 8, 66, 7, –129, 0, 0.9996, 500000, 0
The first element in each list is the name of the coordinate system in quotes. The second 
element in each list is the number that identifies the projection. The remaining elements in the 
list are the parameter values for that particular coordinate system. The elements follow the 
order as outlined in the table “Elements of a Coordinate System” at the beginning of this 
chapter. Each element is separated by commas. 
To create your own coordinate system you will need to add a new entry to the 
MAPINFOW.PRJ file that lists the appropriate elements. The process is described below. 
Creating a New Coordinate System 
To create a new coordinate system for use in MapInfo: 
1. Open MAPINFOW.PRJ in a text editor or word processor. 
2. On a separate line, and following the convention of the other entries list the name for 
the new coordinate system in quotes, followed by a comma. 
3. Add the appropriate numbers for each parameter that pertains to your coordinate 
system. The order of parameters is important. See the table “Elements of a Coordinate 
System” at the beginning of this chapter for the parameters for your coordinate 
system. Separate each parameter with a comma. 
4. If necessary, move your new coordinate system to the appropriate place in the list of 
coordinate systems. For instance, if the new coordinate system applies to a 
hemisphere, put it in the “Projections of a Hemisphere” group. 
5. Save your edited MAPINFOW.PRJ file. 

Chapter 2: Creating Your Own Coordinate System 
Example of a New Coordinate System 
To illustrate this process, consider the following parameters for a coordinate system that you 
want to add to the MAPINFOW.PRJ file: 
Projection Equidistant Conic 
Datum NAD 83 
Units meters 
Origin 30°N, 90°30′W 
Standard Parallels 10°20′N and 50°N 
False Easting 10,000,000 m 
False Northing 500,000 m 
1. Open MAPINFOW.PRJ in a text editor or word processor. 
2. On an empty line, put the name of your new coordinate system in quotes, followed by 
a comma. 
3. Enter the following information to represent your coordinate system: 
6, 74, 7, -90.5, 30, 10.33333, 50, 10000000, 500000
4. Move the entry to its appropriate place among like coordinate systems, if necessary. 
5. Save your edited MAPINFOW.PRJ file. 
You can now use your custom coordinate system just as you would use any of the coordinate 
systems that come with MapInfo. 
Things to keep in mind when editing the MAPINFOW.PRJ file: 
. When specifying projection, datum and units, use the number that represents the 
parameter. These numbers are listed in the table for each parameter earlier in this 
chapter. In our example, 6 represents Equidistant Conic projection; 74 represents NAD 
83 datum, and 7 represents meters. 
. You must record the coordinates in decimal degrees. See Appendix G of the Mapinfo 
Professional User’s Guide for instructions on converting degrees, minutes, seconds, 
into decimal degrees. 
. Remember to include a negative sign for west longitudes and south latitudes. 
. You must list the origin longitude first in the MAPINFOW.PRJ file even though it is 
commonly seen elsewhere following the latitude. 
. Carry out decimals to at least five (5) places for greater accuracy. 
. Do not use commas to represent thousands or millions in large numbers. Only use 
commas to separate parameters from one another. 

Chapter 2: Creating Your Own Coordinate System 
There are other ways you can edit this file. When you want a shorter list remove coordinate 
systems from the file. You can also change the names, change group headings and reorder the 
file to suit your needs. 
Note: Group headings are distinguished by the hyphen at the beginning of the name. 
Names of coordinate systems cannot begin with a hyphen or a space. 
Affine Transformations 
MapInfo provides the ability to define rotated or skewed coordinate systems by allowing an 
optional affine transformation in any coordinate system definition. You can also define a 
coordinate system with bounds and an affine transformation. In that case, add 3000 to the 
projection number, enter the Affine parameters (A,B,C,D,E,F) and then list the bounds 
(x1,y1,x2,y2). The general form is: 
Name, Projection Number + 3000, projection components (from
Appendix F of the MapInfo Professional User’s Guide), Affine 
units, A, B, C, D, E, F, x1, y1, x2, y2
An example of a Mapinfow.prj line with a rotated Affine transformation might look like this 
with the affine parameters in Bold and bounds in Italics: 
”Equal Area for GA (NAD 27)”, 3009, 62, 7, -96, 23, 29.5, 45.5, 0, 0, 0 7, -0.00000000001, 1, -116.071, 
-1, -0.00000000001, -50.53120 , 0 -6972009.20702, -16901023.2253, 26829936.181, 16900922.1627 
Description 
An affine transformation has the following form: 
x’ = Ax + By + C 
y’ = Dx + Ey + F 
In these equations, the base coordinates (x, y) are transformed to produce the derived 
coordinates (x’, y’). The six constants A through F determine the effect of the transformation 
and we use the post multiply method for homogenous 2D coordinate systems. This can be 
considered a matrix operation as follows: 
A B C X X’ 
D E F * Y = Y’ 
0 0 1 1 1 Where (X,Y) and (X’,Y’) are as defined above. 
To do various types of affine transformations the values of A, B, B, D, E, and F need to be 
determined. It is fairly easy to define the basic Transformations, Translations, Rotations, 
Scaling in X, Scaling in Y, Shearing in X and Shearing in Y which can be done using an Affine 
Transformation. 

Chapter 2: Creating Your Own Coordinate System 
Transformation: C and F are the values you want (0, 0) to go to, A=E=1 and B=D=0. So to
move the coordinate system so the origin is at (5, 2) the values would be: A=1, B=0, C=5, D=0,
E=1, and F=2.
Rotation about the origin: A=E=cos(angle to rotate), -B=D=sin(angle to rotate), C=F=0. So to
rotate 60 degree counterclockwise around the origin, A=.5,B=-.866, C=0, D= .866, E= .5, and 
F=0.
To Scale in the X direction: A is the scale you want to use. E =1 and the rest are 0. So to scale to
3 times the size in the X direction the values would be A=3, B=0, C=0, D=0, E= 1, F=0.
To Scale in the Y direction: E is the scale you want to use. A =1 and the rest are 0. So to scale to
5 times the size in the Y direction the values would be A=1, B=0, C=0, D=0, E= 5, F=0.
To Scale Overall just make sure that A and E are equal.
To Shear in the X direction: A = E = 1, B is the shear factor and the rest are 0. So to Shear by 5
units in the X direction then A=1, B=5, C=0, D= 0, E=1, F= 0.
To Shear in the Y direction: A = E = 1, D is the Shear factor and the rest are 0. So to Shear by 4
units in the Y direction then A=1, B=0, C=0, D= 4, E=1, F= 0.
Now to get a general affine transformation, do a pre-matrix multiplication of the basic pieces 
of the transformation. Make sure that you put the first operation on the right. So to Translate 
to (5,2) Rotate 60 degrees and then Shear 5 units in Y and then Translate to (3, 2). The values
would be A=.5, B= -.866, C=6.232, D=3.366, E=-2.23, F=22.758.
Frequently Asked Questions on Projections 
Question: ”What do the \p#### codes mean in the Mapinfow.prj file?”
e.g.: ”--- Australian Map Grid (AGD 66) ---”
”AMG Zone 47 (AGD 66)”, 8, 12, 7, 99, 0, 0.9996, 500000, 10000000
”AMG Zone 48 (AGD 66)\p20248”, 8, 12, 7, 105, 0, 0.9996, 500000, 10000000
Answer: MapInfo uses the \p#### or Projected Coordinate System (PCS) codes shown in the 
above example when registering GeoTIFF images with the GEOREG.MBX utility. GeoTIFF 
files often identify their coordinate system with a single code number instead of listing the 
coordinate system parameters, so GEOREG.MBX scans the MAPINFOW.PRJ file to find a 
matching supported code. MapInfo supports a subset of PCS codes, depending on the 
projection they use, in values between 20000 and 32760). Codes cannot be used more than
once in the mapinfow.prj file. For more information about GeoTIFF files, see 
http://www.remotesensing.org/geotiff/geotiff.html.

Chapter 2: Creating Your Own Coordinate System 
Question: ”How do I convert a coordinate system with units in meters to use feet?” 
Answer: You will need to edit the Mapinfow.prj file to modify the same projection in a 
different measurement system and adjust the False Eastings and Northings used for the 
difference. 
For example below, the first line is the original projection expressed in meters. The second line 
is a copied modification of the first, where the units were changed from ”7” (meters) to ”8” 
(feet) indicating this coordinate system is now using feet, and the False Easting (2000000) and 
Northing (500000) components were divided by .3048 to convert them from meters to feet. 
Example: 
”California, Zone I (1983)\p26941”, 3, 74, 7, -122, 39.3333333333, 40, 41.6666666667, 2000000, 
500000 
”California, Zone I FT (1983)\p26941”, 3, 74, 8 , -122, 39.3333333333, 40, 41.6666666667, 
6561679.7, 164041.99 
Question: ”I chose Longitude/Latitude (NAD 83) as my projection, however, whenever I 
look at the Choose Projection dialog, it keeps saying Longitude/Latitude (GRS 80), why won’t 
my projection change?” 
Answer: The GRS 80 datum is exactly identical to NAD 83 datum. MapInfo uses the numeric 
parameters, not the name, to decide which coordinate system to highlight in the Choose 
Projection dialog. Since GRS 80 has the same numeric parameters as NAD 83, and GRS 80 
comes earlier in the list, MapInfo chooses GRS 80 instead of NAD 83. 
More Information on Projections 
The first three publications listed below are relatively short pamphlets. The last two are
substantial books. We’ve also given addresses and phone numbers for the American Congress
of Surveying and Mapping (the pamphlets) and the U.S. Geological Survey (the books).
American Cartographic Association. Choosing a World Map—Attributes, Distortions, Classes,
Aspects. Falls Church, VA: American Congress on Surveying and Mapping. Special Publication 
No. 2. 1988.
American Cartographic Association. Matching the Map Projection the Need. Falls Church, VA: 
American Congress on Surveying and Mapping. Special Publication No. 3. 1991.
American Cartographic Association. Which Map is Best? Projections for World Maps. Falls
Church, VA: American Congress on Surveying and Mapping. Special Publication No. 1. 1986.

Chapter 2: Creating Your Own Coordinate System 
John P. Snyder. Map Projections—A Working Manual. Washington: U.S. Geological Survey 
Professional Paper 1395. 1987 
John P. Snyder and Philip M. Voxland. An Album of Map Projections. Washington: U.S. 
Geological Survey Professional Paper 1453. 1989. 
Addresses and phone numbers: 
American Congress on Surveying and Mapping 
5410 Grosvenor Lane, Suite 100 
Bethesda, MD 20814–2212 
301–493–0200 
Earth Science Information Center 
U.S. Geological Survey 
507 National Center 
Reston, VA 22092 
703–860–6045 or 1–800–USA–MAPS 
Peter H. Dana of the Department of Geography, University of Texas at Austin has also put up 
an incredible website for explanations of Map projections, Geodetic Datums, and Coordinate 
systems. It is a valuable as many of these explanations were also presented using MapInfo 
Professional. The materials may be used for study, research, and education, but please credit 
the author: 
Peter H. Dana, The Geographer’s Craft Project, Department of Geography, The University of 
Texas at Austin. 
For Geodetic Datum information and explanations, go to 
http://www.utexas.edu/depts/grg/gcraft/notes/datum/datum.html 
For Information on Coordinate systems and other principles, go to 
http://www.utexas.edu/depts/grg/gcraft/notes/coordsys/coordsys.html 
For Information on Map Projections go to 
http://www.utexas.edu/depts/grg/gcraft/notes/mapproj/mapproj.html