Image projection question

Thu Jun 14 19:59:17 PDT 2007

Hi Stephen,

I'm not so sure about the projection definition of your eqc projection.
It doesn't specify a lot of parameters, which makes me think it defaults
to some parameters that may not work too well for Australia.
All I can tell you is that MapServer definitely makes no mistakes with
MGA94 projections in my experience, so that one is definitely right.
I never use the 4283 projection, but rather use 4326 instead. As GDA94
and WGS84 datums are practically equivalent, this works well in my
experience. Your 4283 projection uses a different ellipsoid. I can't
tell whether this is wrong, but knowing that the AGD projections in the
EPSG are incorrect (which also use that ellipsoid), it may be worth you
trying to use 4326 instead.

Please note the subtle differences in acronyms, in case you are not
experienced with AGD84 and GDA94. They are different datums, and all
projections in the EPSG that try to use AGD84 are inaccurate.

Regards,

Jacob

> -----Original Message-----
> From: Stephen Davies [mailto:sdc at sdc.com.au] 
> Sent: 15 June 2007 09:35
> To: Delfos, Jacob
> Cc: Stephen Davies; MAPSERVER-USERS at lists.umn.edu
> Subject: Re: [UMN_MAPSERVER-USERS] Image projection question
> 
> G'day Jacob.
> 
> The map that is displayed by MapServer shows the polygons 
> some 20 m due 
> north of the "correct" location relative to the background raster but 
> the mouse coordinates displayed when pointing at the polygons seem 
> correct (the scale is such that it is difficult to be precise but to 
> five or six decimals they match) but coordinates for features in the 
> raster are wrong; suggesting that the raster projection has "moved" 
> rather than the polygons.
> 
> The Farm Keeper software seems to not accept the embedded 
> georeferencing 
> in the raster as it insists on prompting the user to re-enter 
> georeferencing points.
> 
> It then generates the polygons in what looks like 28354 (Zone 54 
> eastings/northings). These are transformed to 4283 for storage in the 
> database.
> 
> The map uses:
>     PROJECTION
>         "proj=eqc"
>         "lon_0=139.591e"
>     END
> where lon_0 has been calculated as the longitude of the centre of the 
> requested MBR.
> 
> HTH,
> Stephen
> 
> On Friday 15 June 2007 10:30, Delfos, Jacob wrote:
> > Stephen,
> >
> > I'm not completely clear about what has happened to your raster. Can
> > you please clarify whether it appears either moved, or stretched?
> > Also, which projection were you polygons in to begin with? Can you
> > please tell me:
> > - the projection of your polygons
> > - the projection of your map
> >
> > Your raster is in MGA94 (UTM zone 54, GDA datum), which is 
> the common
> > Australian projection, so that's probably fine.
> >
> > Regards,
> >
> > Jacob
> >
> > > -----Original Message-----
> > > From: UMN MapServer Users List
> > > [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On Behalf Of Stephen Davies
> > > Sent: 15 June 2007 08:13
> > > To: MAPSERVER-USERS at LISTS.UMN.EDU
> > > Subject: [UMN_MAPSERVER-USERS] Image projection question
> > >
> > > G'day.
> > > I posted the following last week but had no response. I am
> > > still stuck
> > > without any solution so would really appreciate any feedback
> > > at all as
> > > to what might be wrong with my setup.
> > >
> > >
> > > I have a georeferenced TIFF aerial photo with the gdalinfo below.
> > >
> > > Using a package called Farm Keeper, a shape file was created (by
> > > clicking on the image) containing several polygons defining
> > > paddocks. The shape file was then loaded into PostGIS using
> > > shp2pgsql and the results displayed with MapServer using the
> > > original geotiff as the raster layer.
> > >
> > > The result was "almost right" except each of the polygons was
> > > displayed
> > > about 20m due north of it's correct position relative to the
> > > raster.
> > >
> > > The polygon data is stored transformed to SRID 4283. The map
> > > projection
> > > is eqc with a central meridian of the centre of the polygons' MBR
> > > and the map extent is the MBR plus approx 100m - slightly smaller
> > > than the
> > > raster image extent.
> > >
> > > Looking at the Map Server map coordinates, it appears that
> > > the polygons
> > > are correctly positioned (the mouse coordinates displayed 
> match the
> > > originals) but the raster has been "moved" (stretched 
> north/south).
> > >
> > > Can anybody suggest what has happened?
> > >
> > > Cheers and thanks,
> > > Stephen Davies
> > >
> > >
> > > Driver: GTiff/GeoTIFF
> > > Size is 600, 448
> > > Coordinate System is:
> > > PROJCS["GDA94 / MGA zone 54",
> > >     GEOGCS["GDA94",
> > >         DATUM["Geocentric_Datum_of_Australia_1994",
> > >             SPHEROID["GRS 1980",6378137,298.2572221010042,
> > >                 AUTHORITY["EPSG","7019"]],
> > >             AUTHORITY["EPSG","6283"]],
> > >         PRIMEM["Greenwich",0],
> > >         UNIT["degree (supplier to define
> > > representation)",0.01745329251994328],
> > >         AUTHORITY["EPSG","4283"]],
> > >     PROJECTION["Transverse_Mercator"],
> > >     PARAMETER["latitude_of_origin",0],
> > >     PARAMETER["central_meridian",141],
> > >     PARAMETER["scale_factor",0.9996],
> > >     PARAMETER["false_easting",500000],
> > >     PARAMETER["false_northing",10000000],
> > >     UNIT["metre",1,
> > >         AUTHORITY["EPSG","9001"]],
> > >     AUTHORITY["EPSG","28354"]]
> > > Origin = (370139.138699,6182407.307100)
> > > Pixel Size = (2.00000000,-2.00000000)
> > > Metadata:
> > >   AREA_OR_POINT=Area
> > >   TIFFTAG_DOCUMENTNAME=ER Mapper 7.0
> > >   TIFFTAG_IMAGEDESCRIPTION=ER Mapper GeoTiff raster translator
> > > V1.0: Band 1 = Red, Band 2 = Green, Band 3 = Blue
> > >   TIFFTAG_SOFTWARE=ER Mapper 7.0
> > >   TIFFTAG_XRESOLUTION=0
> > >   TIFFTAG_YRESOLUTION=0
> > > Corner Coordinates:
> > > Upper Left  (  370139.139, 6182407.307) (139d35'8.28"E,
> > > 34d29'30.38"S) Lower Left  (  370139.139, 6181511.307)
> > > (139d35'7.79"E, 34d29'59.46"S) Upper Right (  371339.139,
> > > 6182407.307) (139d35'55.32"E,
> > > 34d29'30.92"S)
> > > Lower Right (  371339.139, 6181511.307) (139d35'54.84"E,
> > > 34d30'0.00"S) Center      (  370739.139, 6181959.307)
> > > (139d35'31.56"E,
> > > 34d29'45.19"S)
> > > Band 1 Block=600x20 Type=Byte, ColorInterp=Red
> > > Band 2 Block=600x20 Type=Byte, ColorInterp=Green
> > > Band 3 Block=600x20 Type=Byte, ColorInterp=Blue
> > >
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> > >
> > > Stephen Davies Consulting                            Voice:
> > > 08-8177 1595
> > > Adelaide, South Australia.                             Fax:
> > > 08-8177 0133
> > > Computing & Network solutions.
> > > Mobile:0403 0405 83
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> -- 
> ==============================================================
> ==========
> This email is for the person(s) identified above, and is 
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> disseminate this email or its contents.
> 
> Stephen Davies Consulting                            Voice: 
> 08-8177 1595
> Adelaide, South Australia.                             Fax: 
> 08-8177 0133
> Computing & Network solutions.                       
> Mobile:0403 0405 83
> 

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