[Proj] Meaning of 7-parameter transformation rotations

Frank Warmerdam warmerdam at pobox.com
Wed Nov 30 12:05:06 EST 2005

On 11/30/05, Martin Vermeer <martin.vermeer at hut.fi> wrote:
> Yes, I know. Just wanted to point out that the above quoted text is
> uninformative. Yes, the exact matrix contains sines and cosines, but of
> the angles Rx, Ry, Rz that are in seconds of arc (and thus, in any
> computation, must be converted to radians first).
> The text following "not in physical units" just expresses the author's
> lack of information, and contains a wrong guess. I propose to replace it
> by correct information.


Thanks, I have updated the paragraph to read:

"The seven parameter case uses <i>delta_x</i>, <i>delta_y</i>, <i>delta_z</i>,
<i>Rx - rotation X</i>, <i>Ry - rotation Y</i>, <i>Rz - rotation Z</i>,
<i>M_BF - Scaling</i>.  The three translation parameters are in meters as
in the three parameter case.  The rotational parameters are in seconds of
arc.  The scaling is apparently the scale change in parts per million."

Does this look OK?  The previous text was intended to highlight my
lack of information.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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