What is prim “Land Impact” value versus “Prim Count?”?
This is a new question for many SLer’s and follows the introduction of mesh to the grid this past August.
Many SL residents still desire to use older viewers like Second Life’s 1.23 Viewer release or Imprudence as a few examples. Thus, when clicking on an object and choosing Edit to see how many prims the object is composed of, your viewer will still likely display this in terms of “prim count.” SL’s Viewer 3 and third party mesh capable viewers like Firestorm and the latest Phoenix release use a new term, which is “Land Impact”, or “LI.” (For awhile, this concept was referred to as “Prim Equivalent Value” or “PEV.” As of January 2011, if you use SL’s Viewer 3.0, you will see the term “Land Impact” when referring to how many prims you may use on a given plot of land.) Casual SLer’s might not yet realize yet what LI means.
I do not claim to be a technical wizard when it comes to these issues, but as a builder, I am becoming aware of how building concepts are now changing. I will try to share with my customers the basic impact of these changes, which you should be very excited about, even if I cannot provide technical reasons for the effects. The long and the short of it is, it is possible to have the same objects on your land, but greatly reduce the prim LI they have.
With the introduction of mesh to the grid in August of 2011, the way prims are calculated had to change. An entire lighthouse may be one mesh object, but if made out of prims, would be composed of several prims. Thus, Linden Lab has developed ways to calculate the prim LI value of objects in Second Life. Basically, the way prim LI is calculated draws upon how an object renders in SL, how complicated the physics calculations are so the object behaves like one would in real life, and what resources the object draws on the server. Others with more technical education could greatly expand on this, or even correct me. For you, as a consumer in SL or a builder, what you need to know is these are new concepts a builder is taking into account when working with regular prims.
Regular ol’ prims, which still have great use for building, can be used slightly differently in construction now. Specifically, when you link more than one regular prim to another, go to the features area of your edit window (in a mesh capable viewer) and apply the convex hull setting, you will see the prim land impact for your 2 prim object reduced to 1. Simple prim cubes essentially can be made to act as .5 prims, like a mesh cube acts.
As I understand it, when applying convex hull, you are applying the most basic physics setting to the prim, meaning it will have none. This is important to remember as if you hollowed a cube to look like an arch because a person would no longer be able to walk through the arch if convex hull is set for that prim. So, how you decide to build your link sets is important. I will explain more about this below.
Many creators are now learning how to use new features to affect prim “Land Impact” value to their advantage. However, there are a few things to remember based on my experiments. If you use a script in the prims that are set to convex hull, you are likely to see your prim LI benefit erased. Thus, you will no longer see my larger houses packaged with an aligner because that requires scripts in all sections of the house. But the benefit my customers will receive in lower LI far outweighs this in my opinion. Also, if you were to accidentally unlink the hull of a house, each of the prims would count as 1 instead of .5. So, a customer needs to take care that they do not accidentally drop a script in their house, which happens, or accidentally unlink the house. You may find your prim count increases to the point you have objects returned to your lost and found folder from your parcel.
For builders, you will find that if you link a sculpt to regular prims set to convex hull, the prim LI will increase substantially. For my Beach House, there are sculpted timber supports that are really 1 prim. When set to convex hull, the prim LI for this 1 prim sculpted object jumps to a LI value of 18! The answer for me in building houses is simply to link the prims that require script use and sculpted prims together and then in a second link set, link the regular prims that compose the hull of the house. The latter is what gets set to convex hull. This might not work well for all products, but it works very well for houses. I have not tested whether this changes how many prims you can include in a link set, which has always been 256.
Many creators will begin to advertise their products with a prim “Land Impact” value as opposed to or along with a prim count value. As described at the beginning of the post if you are using an older viewer, the only way to confirm the object’s affect on your land will be to view how many prims you have available in the About Land menu specific to your land. For example, for my Beach House, an older viewer will show a prim count of 71 when you click on the house and its parts. However, the impact on your land will only be 48 prims because of the way it is constructed. If you are using the newer mesh capable viewers, you will see the “Land Impact” value of 48 as advertised in the edit objects window.
Here’s some other results I have achieved with a few of my own model homes.
The Palm Springs, composed of 454 Prims. The LI value for this home is now only 324 Prims.
The Sedona, composed of 625 Prims. The LI value for this home is now only 392 Prims.
The Hilton Head, composed of 229 Prims. The LI value for this home is now only 158 Prims.
The Koloa, composed of 225 Prims. The LI value for this home is now only 133 Prims.
So, you can see the results that can be achieved.
I have hesitated to jump for joy too much at this development because part of me wonders if Linden Lab will continue to support this. After all, this is effectively making your land cheaper as you can potentially get almost twice the number of prims per your buck than you used to. For now, though, I encourage you to perform your own experiments and see what you come up with. Try this in your builds!
I hope this information is educational and useful to you.