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### Ex1 Task 2

Verfasst: **25. Apr 2012 14:40**

von **Toobee**

Hi,

is the ordering of the tasks fo task 2 correct?

Firstly, I shall write 2 functions hom->cart and cart->hom and

Secondly, draw the transformation+projection matrix out of the blue and

Thirdly, load the 2D-data?

Either I haven't understood the task or the ordering serves confusion

. Do we have to put them in a reasonable order ourselves our is there are reason behind the ordering of to-do's ?

### Re: Ex1 Task 2

Verfasst: **25. Apr 2012 17:05**

von **qgao**

Toobee hat geschrieben:Hi,

is the ordering of the tasks fo task 2 correct?

The first two tasks are independent to the third (load and show 2D points).

Toobee hat geschrieben:Firstly, I shall write 2 functions hom->cart and cart->hom and

Right!

Toobee hat geschrieben:Secondly, draw the transformation+projection matrix out of the blue and

I don't understand "draw the matrix out of the blue". It seems not the task.

### Re: Ex1 Task 2

Verfasst: **25. Apr 2012 17:43**

von **Toobee**

Regarding task 2)

The data obj_2d.mat provides me with x,y points and you provided the steps that were performed on the 3D points?

I shall perform the provided operations on my 2D points and obtain my 3D points, which have the same z-values like those in obj_2d.mat, is that right?

### Re: Ex1 Task 2

Verfasst: **26. Apr 2012 13:03**

von **qgao**

Toobee hat geschrieben:Regarding task 2)

The data obj_2d.mat provides me with x,y points and you provided the steps that were performed on the 3D points?

I shall perform the provided operations on my 2D points and obtain my 3D points, which have the same z-values like those in obj_2d.mat, is that right?

Seems you misunderstand the question.

All the projective transformations from 3D to 2D are already given (or defined). The task is to solve an inverse problem from 2D to 3D.

### Re: Ex1 Task 2

Verfasst: **26. Apr 2012 14:47**

von **Toobee**

The aim is to use the x,y-coordinates and perform the inverse operations?!

apply inverse projection with in/extrinsics on x,y -> add the separatly provided z coordinates, undo the remaining operations. Is that correct?

Sorry for asking so much, but I really have troubles to understand the aim here...

### Re: Ex1 Task 2

Verfasst: **3. Mai 2012 15:08**

von **qgao**

Toobee hat geschrieben:The aim is to use the x,y-coordinates and perform the inverse operations?!

apply inverse projection with in/extrinsics on x,y -> add the separatly provided z coordinates, undo the remaining operations. Is that correct?

Sorry for asking so much, but I really have troubles to understand the aim here...

Right!

### Re: Ex1 Task 2

Verfasst: **4. Mai 2012 00:49**

von **Tigger**

Short Question:

The Task says:

In the file zs.mat you can find the z-coordinates of all transformed 3D points right before the **projection **is applied.

Does this projection refer to the central projection onto the xy-plane or to the single perspective projection which includes all operations (transformations plus projection)?

### Re: Ex1 Task 2

Verfasst: **4. Mai 2012 08:45**

von **Toobee**

the former,

you still have to undo rotation and translation after you added the z-coords to restore the original 3D points.