Re: Geometry and spatial indexes, my opinion

Brandon wrote:
>I agree that this is certainly similar to what I have and that it is
very 
>good. There is however a distinction in that the access traits in my
design 
>are separate from the general point traits. I think that this is an 
>important distinction. When you strip a basic point in N dimensions
from >any 
>nomenclature, you essentially have a data structure that can be
describing >a 
>location in any coordinate frame of dimension N. It is only through
>choosing 
>a coordinate frame that the dimensions of the point takes on meaning
(well, 
>strictly speaking this isn't true... I have a text that speaks quite
highly 
>of coordinate free geometry..). This is why I have created access
traits 
>which are aligned with a particular coordinate frame. It gives me the
means 
>to have a legacy point type (which uses a particular framework, polar 
>coordinates) which can then automatically work in an algorithm which 
>requires Cartesian coordinates. By specializing an access traits type
for 
>the legacy point, I can make all required transformations from r, theta
to 
>x,y without doing any explicit translations to the underlying point
type. 
>The result is that I can put my polar points in and still use all these

>great algorithms which require Cartesian coordinates. Also any outputs
or 
>modifications to inputs are automatically written back in polar
coordinates 
>due to the same interface (via the construct method of the access
traits.)

My point traits above are implicitly for 2D Cartesian points.  You could
specialize it to access a 2D polar coordinate point data type and it
would work similar to what you describe.  I don't provide direct access
to the underlying x and y values, so they can be converted to and from
whatever the point does store in the accessor functions.  I don't have
an N dimensional point concept in my library because I didn't see a need
for such.  If I did, I might very well have come up with a design
similar to yours or what Barend is going to show us soon.  I'm not
opposed to n-dimensional points, I just don't have any use for them,
personally.  

Luke
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