Saturday, February 2, 2008

Prim size limits, linking distance limits and the issue of scale

A while back I wrote a post about the issue of scale in SL As I have been researching in SL, I have come across two limitations of SL that bear on the issue of scale: the size limit of prims, and the distance limits of links. The size limit of prims essentially constrains any particular side of any prim to a range of 10 SL meters, to .0.01 SL meters. That means that a prim can be stretched or shrunk with the simple stretch command such that any one of its side is within 0.01 or 10 meters...not smaller, not greater. The distance link limits actually limits the distance across which different prims can be linked into a single object. How is linking and prim size limitations bear on the scale issue? Say, one wants to visualize a red blood cell, as in my previous post. I could make the red blood cell from a single prim, 10 meters maximum diameter. Or, I could make it out of cuboidal little prims -each 0.01 meters on each side-, linking them into a single object with the prim link command.

From a computer memory and speed standpoint, making the red blood cell out of a single prim is the way to go. That is the fastest and most efficient way of building the cell. But, this would mean the red blood cell is limited in size in SL, from 10 meteres to 0.01 meters. So, from ability to scale things, making them out of individual 0.01 cuboidal units would be the way to go. Except, there may be a limit to the number of prims that can be linked, and the distance over which they can be linked. Is the linking limit distance the same for small prims or for large prims? I need to find out.

Within a single prim, drug concentration can be encoded as a color or texture, but spatial variations in color or texture within the prim would not be possible. So, one would not be able to visualize concentration gradients inside the red blood cell. On the other hand, by making the red blood cell with many cuboidal 0.01 meter prims, a concentration gradient within the red blood cell could be visualized (say, for visualizing diffusion inside the cell, modeling drug transport with partial differential equations). Currently, 1cellPK models we are using do not capture intracellular concentration gradients, so visualizing cells as single (or a few) prims may be the way to go. But, if one makes the red blood cell 10 microns in diameter, than any larger cell that is scaled in relation to the red blood cell would have to be constructed from more than one prim.

In the future, if the intention is to visualize concentation gradients, it may be important to make the cells out of many single prims linked together. Actually, working with cells made out of linked prims may be unavoidable, as that is the way to visualize complex cell shapes (such as that of the red blood cell). But, there may be a limit to the number of prims that can be linked together. As things stand, this is a brief outline of the progress I have made on the scaling problem. I will proceed with more detailed visualization experiments, in terms of constraints on linking prims, and determine the interplay between number of prims, size of prims, and the distance over which prims can be linked.


Peter Miller said...

Re linking, see

Gus Rosania said...

Great!...this saves me a lot of work and I can proceed with my analysis. Thanks Peter!

About Me

I am Assistant Professor at the University of Michigan College of Pharmacy, Department of Pharmaceutical Sciences