[Proj] Define custom proj4 CRS

[Stephane Goldstein]

Hello.

 I have a vectorized version of a map from the Ilhabela http://www.openstreetmap.org/?lat=-23.845&lon=-45.343&zoom=11&layers=M  island in Brazil, dating from 1975.

 I could not find in QGIS the corresponding CRS, so I want to establish it based on the information that is in the PDF version of the map:

 Universal Transverse Mercator Projection

 Units are in kilometers, starting 10.000 km south of the equator (around de south pole), counting towards the north.

 and 500 km west from the 45º W meridian, couting towards the east.

 Horizontal Datum is Corrego Alegre with the Hayford 1924 ellipsoid and origins:

 Latitude 19° 50' 14.91" S
 Longitude 48° 57' 41.98" W 

 Vertical Datum is from Marégrafo de Imbituba, SC, but I don't really understand what are the parameters of the vertical datum that need to be taken in account.

 I would be really thankful if someone can help me to set a proj4 CRS to this map.

 PDF map can be downloaded here ftp://geoftp.ibge.gov.br/mapeamento_sistematico/topograficos/escala_50mil/pdf/sao_sebastiao27963.pdf 

 Vector (DGN) here ftp://geoftp.ibge.gov.br/mapeamento_sistematico/topograficos/escala_50mil/vetor/sao_sebastiao27963/vetor/
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