[Proj] Dubai Palm Island Projection

[Andreas Rappensperger]

2007/3/1, Oscar van Vlijmen <ovv at hetnet.nl>:
>
> > From: "Andreas Rappensperger" <andreas.rappensperger at googlemail.com>
> > Date: Tue, 27 Feb 2007 15:12:05 +0100
> > Subject: [Proj] Dubai Palm Island Projection
>
> > I have the following problem. I would like to rotate the Dubai Palm
> Island so
> > that the palm stand vertical. The rotation point should be the middle
> point
> > of the Palm. In Dubai usually the DLTM projection is used.
> ...
> > Now I tried to define my own coordinate system with the following
> parameter:
> > # DP Dubai Palm (DLTM rotated by -49 degree)
> > proj=omerc lat_0=25.095311 lonc=55.137296 alpha=-49.0000000
> > k=1.000000 x_0=500000.000 y_0=0.000 ellps=WGS84 units=m
> > But it does not work. I have created a test. I have taken two points
> > Bottom of the Palm: 55.154200° 25.102206°
> > Top of the Palm: 55.122691° 25.126338°
> ...
>
> Try the no_rot option, then you'll stay in u,v coordinates, which are with
> respect to the central line.
> With your data I got an angle of -0.93 deg (atan2 of top minus bottom u,v
> coordinates). That's nice because the geodesic azimuth angle between
> top->bottom is not -49 deg but actually -49.923 deg.



Thanks a lot Oscar. The "no_rot" parameter was very helpful for me.
I am using these parameters for me Dubai Palm projection now:

   - ·               proj=omerc
   - ·               lat_0=25.095311
   - ·               lonc=55.137296
   - ·               alpha=-49.5
   - ·               k=1.000000
   - ·               x_0=100000.000
   - ·               y_0=100000.000
   - ·               ellps=WGS84
   - ·               units=m
   - ·               no_rot

But now I am facing with another problem.
I have got a satellite image projected in DLTM with this tfw file
parameters.

   - 1.00000000000000
   - 0.00000000000000
   - 0.00000000000000
   - -1.00000000000000
   - 474701.80520413298000
   - 2782373.47255233210000

Now I have transformed the upper left corner to WGS84 and then to my Dubai
Palm Jumeirah (DPJ) coordinate system.

   - DLTM: 474701.805  2782373.472
   - WGS84: 55.082433 25.147108
   - DPJ: 107933.554 100771.284

Then I have rotated the image though the middle point by 49.5° with GIMP and
created a new tfw file with the upper left corner in DPJ system. With these
two file I have created a web mapping sever with the rotated image.

The Problem is now when I take any point of the rotated image and transform
it back to WGS84 then it is completely wrong. I have transformed the bottom,
top, left and right point of the palm and it seams that the coordinates in
the still rotated in WGS84.

Do you have an idea what I did wrong?

Should I use the towgs84 parameter?
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