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I have made a spiral using geometry nodes, starting from a cube, but as you can see in the image below, its profile is too flat. I'd like it to be more spherical (see red lines). It seems to be a simple task at first glance, but I don't know geo nodes well enough.
This is the node setup I'm using :
I've tried to act on the scale of the last Transform node, without success.
sqrt(x^2 + y^2) = sqrt(1 - z^2). Because the original spiral has a radius of 1 we can just multiply x and y by that factor, and voilà. 
I you want to have an exact sphere, you should go for the solution of lukas_t. But if you just want to have it a bit more spherical and want to play around with the shape, you may take a look at this approach.
Just as lukas_t, this solution starts with a spiral, that has start and end radius set to the same value.
Next we add an offset to the point positions. To calculate this offset, we map the z-position to a value between 0 and $\pi$. This allows us to use the sine function to get a factor, that we apply on the x- and y-position. Finally we use another factor to define the maximum radius of the spiral.
I have another solution that allows you to easily make any shape you like by mapping the XY scale to a float curve.
Spherical:
Custom shape:
Geometry nodes:
Start by setting the Start and End radius to the same value so we have a straight spiral. We then remap our Z position based on the height value. This gives us a 0 to 1 range that goes from the bottom to the top of the spiral. Next we plug that result into a float curve and multiply our X and Y positions by the result. Then combine that with our original Z value.
Now the float curve controls the width of the spiral over its height and you can reshape it however you like.
