Would you like to add this to the documentation?
Formally the referencing documentation asks people to understand what an affine
transform is; providing this background would be more useful.
--
Jody Garnett
On Thursday, 28 April 2011 at 11:34 PM, [email protected] wrote:
> Some times ago I wrote a mail about AffineTransforms, perhaps it
> helps. It is possible to draw pixels using world coordinates. Please
> read below
> ----------------
>
> Some mathematical basics here.
> An affine transform is a powerful mechanism to transform coordinates.
> To get the new
> coordinates x' and y', the following calculation is done.
>
> [ x'] [ m00 m01 m02 ] [ x ] [ m00x + m01y + m02 ]
> [ y'] = [ m10 m11 m12 ] [ y ] = [ m10x + m11y + m12 ]
> [ 1 ] [ 0 0 1 ] [ 1 ] = [ 0 + 0 + 1 ]
>
> A simple example:
> if you want to shift a point 5 units on the x axis and -7 units at the
> y axis, the
> following matrix is needed
>
> [ 1 0 5 ]
> [ 0 1 -7 ]
> [ 0 0 1 ]
>
> Of course, you can say this is easy, x'=x+5 and y'=y-7 would do the same.
>
> Another one, lets do some scaling, say factor 3
>
> [ 3 0 0 ]
> [ 0 3 0 ]
> [ 0 0 1 ]
>
> This is easy too, x'=x*3 and y'=y*3 would the job.
>
> The power of affine transforms is that you can combine multiple
> matrices into a single
> one, doing a set of individual transformations within one step. There
> is a java method
> "concatenate(AffineTransform)" for the AffineTransform class. But be
> careful, given 3
> transformatons A,B,C and you want to combine them in this order, you
> have to go from
> right to left.
> C concatenate B concatenate A will give you the expected result.
>
> A mapping from world coordinates to pixel coordinates needs some
> operations but can be
> done within one affine transformation.
>
> The second powerful feature is that you can create an inverse
> transform (Method
> createInverse), which will do the mapping in the other direction out
> of the box.
>
> Believe me, if you are used to use AffineTransform objects, you will
> use them forever.
>
> Hope this helps
> Cheers
> Christian
> -----------
>
>
> Quoting Francesca Martelli <[email protected]>:
>
> > Hi all,
> > I have a problem with translation from utm coordinates in screen pixel
> > position. I have already seen the tutorials (world2screen,
> > data2world...), but examples reported there seem do not work in my case.
> >
> > I have a mapContext with shapefiles in a jmappane, and I would like to
> > paint a point (with position expressed in UTM coordinates) over the map.
> >
> > Any help is greatly appreciated.
> > Francesca
> >
> >
> > --
> > Francesca Martelli, Computer Science Ph.D.
> > Algorithms and Computational Mathematics Group, IIT - CNR, Pisa
> > Phone: +39 050 315 3191 (office), +39 050 315 2333 (fax)
> > http://www.iit.cnr.it/francesca.martelli/
> > email: [email protected]
> >
> >
> >
> > ------------------------------------------------------------------------------
> > WhatsUp Gold - Download Free Network Management Software
> > The most intuitive, comprehensive, and cost-effective network
> > management toolset available today. Delivers lowest initial
> > acquisition cost and overall TCO of any competing solution.
> > http://p.sf.net/sfu/whatsupgold-sd
> > _______________________________________________
> > Geotools-gt2-users mailing list
> > [email protected]
> > https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
>
>
>
> ----------------------------------------------------------------
> This message was sent using IMP, the Internet Messaging Program.
>
>
>
> ------------------------------------------------------------------------------
> WhatsUp Gold - Download Free Network Management Software
> The most intuitive, comprehensive, and cost-effective network
> management toolset available today. Delivers lowest initial
> acquisition cost and overall TCO of any competing solution.
> http://p.sf.net/sfu/whatsupgold-sd
> _______________________________________________
> Geotools-gt2-users mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
>
------------------------------------------------------------------------------
WhatsUp Gold - Download Free Network Management Software
The most intuitive, comprehensive, and cost-effective network
management toolset available today. Delivers lowest initial
acquisition cost and overall TCO of any competing solution.
http://p.sf.net/sfu/whatsupgold-sd
_______________________________________________
Geotools-gt2-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
