Question about Italian conversion

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Question about Italian conversion

Massimo De Marchi
Hi,
I am a new user, and was performing image conversion with gdalwarp
between old Italian c.s. (Gauss Boaga) and WGS 84.

I found there is a shift (around 100m)in the conversion. I tested with
cs2cs and I have the same issue.
The coordinate conversion is the same using both EPSG 3003 or 26591, or
using the proj4 string taken form spatialreference.org

Starting with 1641163 East and 4997349 North I get
10d47'40.422"E  45d6'52.824"
in place of:
10d47'39.5"E    45d6'55.2"

What am I doing wrong?

Thanks in advance,
Massimo

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Re: Question about Italian conversion

OvV_HN
> From: Massimo De Marchi
> Date: Mon, 24 Dec 2007 10:43:16 +0100
> Subject: [Proj] Question about Italian conversion
>
> Hi,
> I am a new user, and was performing image conversion with gdalwarp
> between old Italian c.s. (Gauss Boaga) and WGS 84.
>
> I found there is a shift (around 100m)in the conversion. I tested with
> cs2cs and I have the same issue.
> The coordinate conversion is the same using both EPSG 3003 or 26591, or
> using the proj4 string taken form spatialreference.org
>
> Starting with 1641163 East and 4997349 North I get
> 10d47'40.422"E  45d6'52.824"
> in place of:
> 10d47'39.5"E    45d6'55.2"
>
> What am I doing wrong?

Trying to follow the procedure with independent software, I get the
impression that you didn't transform the datum from Hayford to WGS84.
You simply inverse projected from x,y to lon,lat with the proper transverse
mercator projection.
With the Roma40 transform parameters found at <http://crs.bkg.bund.de>
I arrive at lat,lon:
45d 06m 55.252s,  10d 47m 39.415s
assuming a position vector rotation model (ISO) and an initial height of 0.
The proj/epsg definitions you mention don't contain any datum transform
instructions.


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Re: Question about Italian conversion

Massimo De Marchi
Scrive Oscar van Vlijmen <[hidden email]>:

> > From: Massimo De Marchi
> > Date: Mon, 24 Dec 2007 10:43:16 +0100
> > Subject: [Proj] Question about Italian conversion
> >
> > Hi,
> > I am a new user, and was performing image conversion with gdalwarp
> > between old Italian c.s. (Gauss Boaga) and WGS 84.
> >
> > I found there is a shift (around 100m)in the conversion. I tested with
> > cs2cs and I have the same issue.
> > The coordinate conversion is the same using both EPSG 3003 or 26591, or
> > using the proj4 string taken form spatialreference.org
> >
> > Starting with 1641163 East and 4997349 North I get
> > 10d47'40.422"E  45d6'52.824"
> > in place of:
> > 10d47'39.5"E    45d6'55.2"
> >
> > What am I doing wrong?
>
> Trying to follow the procedure with independent software, I get the
> impression that you didn't transform the datum from Hayford to WGS84.
> You simply inverse projected from x,y to lon,lat with the proper transverse
> mercator projection.
> With the Roma40 transform parameters found at <http://crs.bkg.bund.de>
> I arrive at lat,lon:
> 45d 06m 55.252s,  10d 47m 39.415s
> assuming a position vector rotation model (ISO) and an initial height of 0.
> The proj/epsg definitions you mention don't contain any datum transform
> instructions.
>
>

Thanks for your answer. I tried to do a coordinate transform using the -s_srs
EPSG:3003 (or 26591) and -t_srs EPSG:4326 parameters. How can I add the
necessary datum transform? I checked the documentation amd the forum, but
didn't find a clue.

Regards,
Massimo

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Re: Question about Italian conversion

Frank Warmerdam
[hidden email] wrote:

>
>>> What am I doing wrong?
>> Trying to follow the procedure with independent software, I get the
>> impression that you didn't transform the datum from Hayford to WGS84.
>> You simply inverse projected from x,y to lon,lat with the proper transverse
>> mercator projection.
>> With the Roma40 transform parameters found at <http://crs.bkg.bund.de>
>> I arrive at lat,lon:
>> 45d 06m 55.252s,  10d 47m 39.415s
>> assuming a position vector rotation model (ISO) and an initial height of 0.
>> The proj/epsg definitions you mention don't contain any datum transform
>> instructions.
>>

> Thanks for your answer. I tried to do a coordinate transform using the -s_srs
> EPSG:3003 (or 26591) and -t_srs EPSG:4326 parameters. How can I add the
> necessary datum transform? I checked the documentation amd the forum, but
> didn't find a clue.

Massimo,

I followed Oscar's link to http://crs.bkg.bund.de but did not see any easily
identifiable datum transformation parameters for the Monte Mario datum.
However, if you can find some appropriate ones they can be specified in the
PROJ.4 string.  EPSG:3003 expands to:

+proj=tmerc +lat_0=0 +lon_0=9 +k=0.9996 +x_0=1500000 +y_0=0 +ellps=intl
+units=m +no_defs

To add datum shift parameters you might use a string like:

+proj=tmerc +lat_0=0 +lon_0=9 +k=0.9996 +x_0=1500000 +y_0=0 +ellps=intl
+units=m +towgs84=100,50,25 +no_defs

Insert whatever towgs84 parameter you find are appropriate to the datum.

Best regards,

--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, [hidden email]
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org



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Re: Question about Italian conversion

Markus Neteler
On Dec 29, 2007 8:54 PM, Frank Warmerdam <[hidden email]> wrote:

> [hidden email] wrote:
> >
> >>> What am I doing wrong?
> >> Trying to follow the procedure with independent software, I get the
> >> impression that you didn't transform the datum from Hayford to WGS84.
> >> You simply inverse projected from x,y to lon,lat with the proper transverse
> >> mercator projection.
> >> With the Roma40 transform parameters found at <http://crs.bkg.bund.de>
> >> I arrive at lat,lon:
> >> 45d 06m 55.252s,  10d 47m 39.415s
> >> assuming a position vector rotation model (ISO) and an initial height of 0.
> >> The proj/epsg definitions you mention don't contain any datum transform
> >> instructions.
> >>
>
> > Thanks for your answer. I tried to do a coordinate transform using the -s_srs
> > EPSG:3003 (or 26591) and -t_srs EPSG:4326 parameters. How can I add the
> > necessary datum transform? I checked the documentation amd the forum, but
> > didn't find a clue.
>
> Massimo,
>
> I followed Oscar's link to http://crs.bkg.bund.de but did not see any easily
> identifiable datum transformation parameters for the Monte Mario datum.

Here they are (extracted from GRASS GIS source code):

datum.table:rome40      "Monte_Mario"
international dx=-225     dy=-65      dz=9
datumtransform.table:rome40
"towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68" "Italy
(Peninsular Part)" "Accuracy 3-4m"
datumtransform.table:rome40
"towgs84=-168.6,-34.0,38.6,-0.374,-0.679,-1.379,-9.48" "Italy
(Sardinia)" "Accuracy 3-4m"
datumtransform.table:rome40
"towgs84=-50.2,-50.4,84.8,-0.690,-2.012,0.459,-28.08" "Italy (Sicily)"
"Accuracy 3-4m"

They were taken from http://crs.bkg.bund.de.

See also:
http://it.wikipedia.org/wiki/Proiezione_di_Gauss-Boaga

Hope this helps,
Markus
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Re: Question about Italian conversion

Massimo De Marchi
Thanks for the help!

Massimo

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Re: Question about Italian conversion

D_Guidi
Massimo De Marchi wrote
Thanks for the help!
Did you have resolved the problem?
I'm trying to fix the conversion from Monte Mario to WGS 84, with gdal I have noticed some conversion errors.
Could you send me the correct parameters to insert in proj definitions?
Thanks ;)