[Geowanking] 3D geodata for Dublin?

[stephen white]

On 10/05/2007, at 7:52 AM, Paul Ramsey wrote:
> Building 3D city models is an expensive business, that's why the  
> Big Boys pay Big Money for it.  Lacking anything to grasp at all in  
> your input data, like stereo pairs, etc, leaves you in a bad  
> state.  All I can suggest is to gut it out and collect the building  
> tops through digitization, then use those shadows to your  
> advantage. Take reference heights on a few buildings, then use the  
> shadow lengths on the rest to derive the building heights.

Two things to be careful about...

	Time is still moving when the plane is flying along for the aerials,  
so the shadows at the beginning of a run is slightly different from  
the end of the run. You will need to calculate sun angle and slowly  
slide it through a complete run.

	Aerial photographs bought as tiles are an amalgamation of  
overlapping images, so you would need to obtain the raw tiles  
directly from the camera in order to calculate shadow angles. Those  
raw tiles will give you the time for shadow calculations too.

Speaking for myself, I would give up trying to extract 3d images from  
aerial photographs and just go through the streets to obtain the data  
you need (which is the approach the big boys use with LIDAR cameras).

Much more likely is that the local council already has the building  
data in order to handle building permit approvals and other activities.

--
   steve at adam.com.au