paolo zatelli alfonso vitti - unitn.itzatelli/remote_sensing/cartographic_projections.pdf ·...

Cartographic Projections


Paolo Zatelli Alfonso Vitti

Dept. Civil and Environmental Engineering

University of Trento

Paolo Zatelli | University of Trento | 1 / 18


Outline

1 Cartographic projection

2 Cartographic projection used in Italy


Cartographic Projections | Cartographic projection

Cartographic systems

To create a map it is necessary to choose:

the reference system and the associated ellipsoid (Datum)a set of coordinates and measures that realize the adoptedreference systemthe cartographic projection and the related parameters



Cartographic systems

To give cartographic coordinates a meaning we have to “label”numbers with information about:

the datumthe cartographic projection

While datum and the cartographic projection are distinct and differentdatum/projection combinations are possible, it is common to providesimply the cartographic projection leaving the Datum implied.

For example, the UTM projection is used both with the global referencesystem WGS84 and with the ED50.



Proiezioni cartografiche

Cartographic projections “transport” coordinates from an ellipsoid to acartographic plane.

The two surfaces are not equivalent from a topological viewpoint, i.e., itis not possible to “transport” from one surface to the other withoutdeformations.

It is possible:

to preserve angles (conformal maps)to preserve surfaces (equivalent maps)to minimize the deformation, without having none of them actuallynull (compromise maps)


Cartographic Projections | Cartographic projection used in Italy

Cartographic projection used in Italy

The more common projections used in Italy are:

UTM (Universal Trasversal Mercator)Gauss-Boaga, official Italian national projectionCassini-Soldner, used for the Nuovo Catasto dei Terreni italiano(new Italian Cadaster)



UTM Projection

It is a Gauss map so:

it is conformalalong the central meridian, the scale factor is constantmeridians and parallels are perpendicularit is symmetrical wrt the equator



UTM Projection

The projection can be depicted as the projection of the ellipsoid to an“horizontal” cylinder (tangent to a meridian)



UTM Projection

Since deformations increase moving away from the tangentialmeridian:

the projection is performed using 6◦ wide zonesthe central meridian has a scale factor of 0.9996the East coordinate of the central meridian is set to 500000 mthe projection is bounded in the latitude range [−80◦; +80◦]



UTM Projection

UTM zones



UTM ProjectionThe Italy falls in zones 32 and 33. A small part is in the zone 34



UTM Projection

This projection is used:

in the official Italian cartography in ED50to express the coordinates of a GPS survey, usually labeledsimply as WGS84 (should be UTM-WGS84)



Gauss-Boaga projection I

It is a Gauss projection:

there are only two zones (“fusi” in Italian) of 6◦30′, “Ovest” and“Est” that correspond to the UTM zones 32 and 33

the central meridian has a scale factor of 0.9996

the East coordinate of the first meridian is set to 1500000 mwhereas the East coordinate of the second meridian is set to2520000 m



Gauss-Boaga projection II



Double parametrization - IGM 1:25000



Double parametrization - CTP PAT


Cartographic Projections | Appendice | Bibliografia

Bibliografia

Benciolini B., 2004, Dispensa sui sistemi di riferimento, comunicazionepersonale.

Monti C., 1984, Elementi di cartografia con riferimenti alla situazionecartografica in Italia, in “Spazi verdi territoriali. Corso post-laurea diformazione professionale - Milano, 1983”, pp. 92-142, Franco Angelieditore, Milano, 1984.


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