As an tutorial here
http://docs.geotools.org/latest/userguide/index.html ?
Title: Affine Transform
But before I start I should be able to build the docs
mvn clean install produces an error
[exec] reST markup error:
[exec] /home/christian/gt-trunk/docs/user/faq.txt:18: (SEVERE/4)
Problems with "include" directive path:
[exec] IOError: [Errno 2] No such file or directory: '/welcome/faq.txt'.
Some hints ?
Quoting Jody Garnett <[email protected]>:
> 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]
>> >
>> >
>> >
>> >
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>>
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