4

I have a shapefile in a Cassini Soldner reference system centered in Monte Mario (Italian cadastre map). I want to insert these data inside QGIS in order to compare data with aerial images. When importing the file I have to select the reference system, but I'm not sure how to proceed. I have noticed that the EPSG code for the Cassini Soldner representation is the 9806, but:

  1. EPSG 9806 is not included in QGis, how I can import it?
  2. Even if I successfully import it on QGis, how I can center it in Monte Mario Origin?

I am just a newbie about GIS, so please be understanding.

Improve this question

1 Answer 1

Reset to default
6

EPSG:9806 is the transformation method called Cassini-Soldner, but this is not the kind of EPSG code that includes the transformation parameters which are necessary for QGIS.

Usually, shapefile datasets include a .prj file with the CRS information. If you do not have it, you might go back to the place where you got the data from and look for further information.

Filtering the QGIS CRS list for Monte Mario, you get a bunch of 7 transverse mercator projections covering parts of Italy. The main CRS are based on the 9° (EPSG:3003 zone 1) and 15° (EPSG:3004 zone 2) meridian. CRS with prime meridian through Rome and the region Emilia Romagna have separate CRS definitions.

You need the center coordinates of the 31 local Cassini Soldner projections, which you can find here: https://web.archive.org/web/20210506151119/https://www.globogis.it/le-origini-delle-coordinate-cassini-soldner

Note that the given Eastings are not based on the Greenwich meridian, but on local datums used, which you can find here: https://web.archive.org/web/20220120085646/https://www.globogis.it/i-datum-catastali-italiani

You will have to add datum and center eastings, and transform the degree-minute-second values into decimal degrees for lat and lon.

With that, you can build your local CRS:

+proj=cass +lon_0=.... +lat_0=.... +x_0=0 +y_0=0 +ellps=bessel +units=m +no_defs

You might have to add a datum shift to switch from the bessel ellipsoid to WGS84.

Improve this answer
2
  • Thank you. I have created my local CRS using:+proj=cass +lon_0=12.4521272222222 +lat_0=41.9244030555555 +x_0=0 +y_0=0 +ellps=WGS84 +units=m +no_defs
    – Samuele
    May 4, 2015 at 13:46
  • 2
    This might be wrong because the old cassini soldner projections did not use the WGS84 ellipsoid, but the bessel ellipsoid. You better add +towgs84 parameters.
    – AndreJ
    Nov 11, 2016 at 6:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.