Javier,
You can use two lm-models for that. One for each coordinate. Then use
predict() to calculate the coordinates of the other points. And by the
way: four points is not very much data to calculate a transformation. I
mlight work if the image is not very much distorted and you have precise
measurement of the reference points coordinates.
corners.px <- matrix(c(212.5, 275.5, 562.5, 275.5, 212.5, 625.5, 562.5,
625.5), ncol = 2, byrow = TRUE)
corners.r <- matrix(c(139463, 8386, 139579, -1294, 131921, 8180, 132002,
-1256), ncol = 2, byrow = TRUE)
dataset <- data.frame(cbind(corners.px, corners.r))
colnames(dataset) <- c("X", "Y", "U", "V")
lm(U ~ X + Y, data = dataset)
lm(V ~ X + Y, data = dataset)
HTH,
Thierry
PS R-sig-GEO would be more suitable for this kind of question.
------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
[EMAIL PROTECTED]
www.inbo.be
Do not put your faith in what statistics say until you have carefully
considered what they do not say. ~William W. Watt
A statistical analysis, properly conducted, is a delicate dissection of
uncertainties, a surgery of suppositions. ~M.J.Moroney
-----Oorspronkelijk bericht-----
Van: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
Namens [EMAIL PROTECTED]
Verzonden: dinsdag 22 januari 2008 9:56
Aan: r-help@r-project.org
Onderwerp: [R] geometric transformation
Hi everyone,
I've got a set of thousands points (2D) located on a pixel image, and I
know that four points in this pixels image correspond to four points in
a
real space on which I need to locate the mapping of all the thousand
source points from the pixel set.
For this I've got four reference points (corners.px), and the
corresponding four destination points (corners.r):
> corners.px
[,1] [,2]
[1,] 212.5 275.5
[2,] 562.5 275.5
[3,] 212.5 625.5
[4,] 562.5 625.5
> corners.r
[,1] [,2]
[1,] 139463 8386
[2,] 139579 -1294
[3,] 131921 8180
[4,] 132002 -1256
I think I must find a transformation matrix and apply this
transformation
matrix to all the set in the pixel space, but cannot find the way to
contruct this transformation matrix.
I guess this is not a question just pertaining to R, but perhaps you can
help me with this.
Thank you and best regards!
Javier
-----
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