To define the Project
Cartographic Projection
The "Projections"
window will be used always when the user is creating
a project, calibrating
a digitizing table (when the map projection is different then the one in the active
project), or registering an image.
The projection has to be
correctly defined, because wrong parameters can compromise the data posterior
usage. Because of this, it is suggested to check additional information about
the cartographical concepts and projections.
Defining a Projection:
-
Select the Projection System
and the Earth Model or Datum ( See how to add other Earth
Models);
-
Give the required parameters (Hemisphere, source Latitude, source Longitude (or ZONE in an
UTM Projection), Scale Factor, Standard parallel, Offsets), according to the Projection
System selected. The Table below shows the parameters typically required
in each projection;
-
Click on Execute
to confirm the projection to be used.
Note:
The zone is a
parameter that defines a slice with 6 degrees of amplitude for longitude in
the UTM projection. The Earth is divided into 60 zones of 6 degrees and each
zone has a reference meridian, called central meridian. The zones are
numbered from 1 to 60, from west to east starting at the Greenwich
anti-meridian. The zone or
central meridian has to be known so it is possible to make the conversion
between geographical coordinates and UTM coordinates.
Creating a project.
Parameters requested when a projection is selected.
Projection
|
Earth Model
|
Source
|
Parallel Standard
|
Comments
|
NOProjection

|
-
|
-
|
-
|
There is no projection.
It can be used to any defined area in a planar coordinate system. Offsets are user defined.
|
UTM

|
SAD 69
Hayford/Corrego Alegre
Hayford
Clark
Astro-Chua
WGS84
|
Long
(*)
|
-
|
It is used in
topographical charts. The source longitude corresponds to the central meridian
of the UTM zone. Values for Brazil
are: 33W, 39W, 45W, 51W, 57W, 63W, 69W or 75W. It uses offsets and a scale
factor that can not be changed by the user. It is a conforming projection that keeps the angles.
|
Mercator

|
SAD 69
Hayford/Corrego Alegre
Hayford
WGS84
|
Long
(*)
|
Prim.Lat.
|
Used for nautical
charts. The longitude source can be any value, because the meridians are
represented by straight lines equally spaced. Offsets are user defined. The
standard parallel (Prim. Lat.) is usually indicated with the nautical chart
scale. It is a conforming projection that keeps the angles.
|
Gauss

|
SAD 69
Hayford/Corrego Alegre
Hayford
WGS84
|
Long
(*)
|
-
|
In Brazil
, it
was used in old topographical charts. The source longitude corresponds to
the central meridian or Gauss zone. Values for
Brazil
are: 36W, 42W, 48W, 54W,
60W, 66W or 72W. Offsets and the scale factor used in
Brazil
are
presented by default, but the user can change the values. It is known in
several countries as the Transverse Mercator projection. It is a conforming projection that keeps the angles.
|
Lambert Million

|
SAD 69
Hayford/Corrego Alegre
Hayford
WGS84
|
Long
(*)
|
- (**)
|
It is the standard for millionth
chart (4 x 6 degrees). Source longitude for Brazil
: 54W. It requires to
inform the involving rectangle so the projection parameters are automatic
computed. Offsets are user defined. It is a conforming projection that
keeps the angles.
|
Lambert

|
SAD 69
Hayford
Clark
WGS84
|
Lat.
Long.
|
Prim. Lat
Sec. Lat
|
It is used in millionth
charts and in aeronautical charts. Different than the Lambert Million,
requires the user to define all projection parameters. Offsets are user
defined. It is a conforming projection that keeps the angles.
|
Polyconic

|
SAD 69
Hayford
WGS84
|
Lat.
Long.
|
-
|
It is used in thematic
maps and political maps in small scales. The source latitude normally is
the Equator line. The longitude source value for Brazil
is 54W. Offsets are user
defined. It is neither conforming nor an equivalent projection.
|
Cylindrical

|
Sphere
R=6371 Km
|
Long
(*)
|
Prim.Lat.
|
It is used for mapping
in small scales. The standard parallel (Prim. Lat) normally is the Equator
line. Offsets are user defined. It is an equidistant projection through out
the standard parallel.
|
Polar Stereographic

|
Hayford
WGS84
|
Long.
(*)
|
-
|
It is used for polar regions
mapping. It is required to inform if the projection plan is in the North or
South Hemisphere. Offsets are user defined. It presents a default scale
factor, but the user can change its value. It is a conforming projection that keeps the angles.
|
Bipolar

|
Sphere
R=
6371220 m
|
-
|
-
|
It is named Bipolar
Oblique Conical Conformal , it is used for the American continents mapping.
Offsets are user defined. As the name indicates it is a conforming
projection that keeps the angles.
|
Albers

|
SAD 69
Hayford
WGS84
|
Lat.
Long.
|
Prim.Lat.
Sec.Lat.
|
It can be used in
thematic mapping requiring a precise area computation. All the projection
parameters are provided by the user. Offsets are also user defined. It is an equivalent projection that keeps the
areas.
|
Miller

|
Sphere
R=
6371 km
|
Long.
(*)
|
-
|
It is used for mapping
in small scales. Offsets are user defined. The projection is neither
conform nor equivalent.
|
LatLong
|
SAD 69
Corrego Alegre
Hayford
Clarke-1866
WGS84
|
-
|
-
|
It is used for data in
the matrix format (images and grids) with spatial resolution established in
decimal degrees. For obvious reasons, the offsets are zero and it can not
be changed by the user. The projection is neither conform nor equivalent.
|
Sinusoidal
|
Sphere
R=
6371 km
|
-
|
-
|
It can be used in
thematic mappings in small scales requiring precise area computation.
Offsets are user defined. It is an equivalent projection that keeps the
areas.
|
(*) - The Equator line is the axis for the source Latitude.
(**) - The standard parallel
(Primary and Secondary Latitudes) are computed by the system.
NOTE: See also table with other characteristics for each projection handled by the
SPRING.
See also:
Creating a Project
Calibrating
a Digitizing Table
Registering
an Image
|