OSGeo.org › OSGeo Software and Data Projects › GeoTools, the java GIS toolkit › geotools-gt2-users

Reprojection problem

6 messages

Reprojection problem

Reply Threaded

Hi All, I have two shape files, having UTM 11C(EPSg : 32711) and WGS 84(EPSG : 4326) projections. When I open them in a map, then they overlap in the UTM projection, but when I change the projection to WGS 84 then they don't overlap. I don't know whats the problem, because I think, if the layers overlap in one projection then they must overlap in other projections also. Please help in this regard. I am attaching the files for your reference.

--
Thanks,
Rahul

------------------------------------------------------------------------------
Come build with us! The BlackBerry® Developer Conference in SF, CA
is the only developer event you need to attend this year. Jumpstart your
developing skills, take BlackBerry mobile applications to market and stay
ahead of the curve. Join us from November 9-12, 2009. Register now!
http://p.sf.net/sfu/devconf
_______________________________________________
Geotools-gt2-users mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users

test reprojection.zip (3K) Download Attachment

Jody Garnett-2

Re: Reprojection problem

Reply Threaded

Hi Rahul:

Your data set seems to be quite far south at -82.493. That far south
lat long coordinates can be pretty numerically unstable as your
example shows.

I went through replacing your CRS definition from your prj file with
the official definition from the EPSG database and was able to get
your two rectangles to take on different shapes.

Thanks for attaching the files; you may also wish to compare the
result with uDig 1.2 M6 vs uDig 1.2 M7 since we upgraded the EPSG code
definitions.

Jody

On 23/09/2009, at 6:23 PM, Rahul... हम पंछी
उन्मुक्त गगन के wrote:

> Hi All, I have two shape files, having UTM 11C(EPSg : 32711) and WGS
> 84(EPSG : 4326) projections. When I open them in a map, then they
> overlap in the UTM projection, but when I change the projection to
> WGS 84 then they don't overlap. I don't know whats the problem,
> because I think, if the layers overlap in one projection then they
> must overlap in other projections also. Please help in this regard.
> I am attaching the files for your reference.
>
> --
> Thanks,
> Rahul
> <test reprojection.zip>

------------------------------------------------------------------------------
Come build with us! The BlackBerry® Developer Conference in SF, CA
is the only developer event you need to attend this year. Jumpstart your
developing skills, take BlackBerry mobile applications to market and stay
ahead of the curve. Join us from November 9-12, 2009. Register now!
http://p.sf.net/sfu/devconf
_______________________________________________
Geotools-gt2-users mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users

mbedward

Re: Reprojection problem

Reply Threaded

In reply to this post by Rahul... हम पंछी उन्मुक्त गगन के

Hi Rahul,

I've just had a quick look at your shapefiles and they overlap in both
projections when I display them, although to different extents. In UTM
they overlap closely while in WGS 84 they only overlap partially.

WGS84 screen snap http://imagebin.org/64909

UTM screen snap http://imagebin.org/64910

But it sounds like this is different to what you are seeing...

Michael

------------------------------------------------------------------------------
Come build with us! The BlackBerry® Developer Conference in SF, CA
is the only developer event you need to attend this year. Jumpstart your
developing skills, take BlackBerry mobile applications to market and stay
ahead of the curve. Join us from November 9-12, 2009. Register now!
http://p.sf.net/sfu/devconf
_______________________________________________
Geotools-gt2-users mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users

Jody Garnett-2

Re: Reprojection problem

Reply Threaded

I loaded them up in uDig and see exactly the same results. By
replacing the CRS from the "prj" file with the projection of the same
name from the EPSG database I was able to narrow the difference a bit
more.

Jody

On 23/09/2009, at 8:04 PM, Michael Bedward wrote:

> Hi Rahul,
>
> I've just had a quick look at your shapefiles and they overlap in both
> projections when I display them, although to different extents. In UTM
> they overlap closely while in WGS 84 they only overlap partially.
>
> WGS84 screen snap http://imagebin.org/64909
>
> UTM screen snap http://imagebin.org/64910
>
> But it sounds like this is different to what you are seeing...
>
> Michael

Rahul... हम पंछी उन्मुक्त गगन के

Re: Reprojection problem

Reply Threaded

In reply to this post by Jody Garnett-2

Hi Jody, So now as you have seen the behaviour, can you tell me what is the problem? Why those two layers don't overlap in different projections? Is this a bug or it is meant to happen that way?

2009/9/23 Jody Garnett <[hidden email]>

Hi Rahul:

Your data set seems to be quite far south at -82.493. That far south lat long coordinates can be pretty numerically unstable as your example shows.

I went through replacing your CRS definition from your prj file with the official definition from the EPSG database and was able to get your two rectangles to take on different shapes.

Thanks for attaching the files; you may also wish to compare the result with uDig 1.2 M6 vs uDig 1.2 M7 since we upgraded the EPSG code definitions.

Jody

On 23/09/2009, at 6:23 PM, Rahul... हम पंछी उन्मुक्त गगन के wrote:

Hi All, I have two shape files, having UTM 11C(EPSg : 32711) and WGS 84(EPSG : 4326) projections. When I open them in a map, then they overlap in the UTM projection, but when I change the projection to WGS 84 then they don't overlap. I don't know whats the problem, because I think, if the layers overlap in one projection then they must overlap in other projections also. Please help in this regard. I am attaching the files for your reference.

--
Thanks,
Rahul
<test reprojection.zip>

--
Thanks,
Rahul

------------------------------------------------------------------------------
Come build with us! The BlackBerry® Developer Conference in SF, CA
is the only developer event you need to attend this year. Jumpstart your
developing skills, take BlackBerry mobile applications to market and stay
ahead of the curve. Join us from November 9-12, 2009. Register now!
http://p.sf.net/sfu/devconf
_______________________________________________
Geotools-gt2-users mailing list
[hidden email]
https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users

Jody Garnett-2

Re: Reprojection problem

Reply Threaded

Some javascript/style in this post has been disabled (why?)

You also reported this problem on the geotools list; thus far we are all seeing the same results. Your data is so far north as to be not very deterministic; if you get the real definitions from the database things improve (since it has access to more accurate transforms).

It would be helpful to drop this over as raster background or something as a reference point. I cannot be sure if you are looking at a bug; or if you are looking at a fact of life with your data.

Jody

On 23/09/2009, at 9:27 PM, Rahul... हम पंछी उन्मुक्त गगन के wrote:

Hi Jody, So now as you have seen the behaviour, can you tell me what is the problem? Why those two layers don't overlap in different projections? Is this a bug or it is meant to happen that way?

2009/9/23 Jody Garnett <[hidden email]>
Hi Rahul:

Your data set seems to be quite far south at -82.493. That far south lat long coordinates can be pretty numerically unstable as your example shows.

I went through replacing your CRS definition from your prj file with the official definition from the EPSG database and was able to get your two rectangles to take on different shapes.

Thanks for attaching the files; you may also wish to compare the result with uDig 1.2 M6 vs uDig 1.2 M7 since we upgraded the EPSG code definitions.

Jody

On 23/09/2009, at 6:23 PM, Rahul... हम पंछी उन्मुक्त गगन के wrote:

Hi All, I have two shape files, having UTM 11C(EPSg : 32711) and WGS 84(EPSG : 4326) projections. When I open them in a map, then they overlap in the UTM projection, but when I change the projection to WGS 84 then they don't overlap. I don't know whats the problem, because I think, if the layers overlap in one projection then they must overlap in other projections also. Please help in this regard. I am attaching the files for your reference.

--
Thanks,
Rahul
<test reprojection.zip>

--
Thanks,
Rahul