Why are mesh prim totals different when linked (i.e. not the sum of added prims)

[Argus Zimmer]

Ok so here's the issue I have a project un linked it consist of 3 identical somewhat box shaped meshes each 1+ impact and another curved tube object again 1+ impact and 3 standard prim cylinders now apart adding prims up it comes to 9 even taking into account the fractions involved with the meshes, now here's the rub when I'm link these objects the prim total for the linked object reports as 97 impact, now IM not great at math but HUH  !!

Thanks for your time and attention

ARGUS

[Rolig Loon]

For each object in the Second Life world, Second Life compares three important performance factors: download weight, physics weight, and server weight. It then chooses the highest of these weights and assigns it to the object as that object's land impact rating.

Here's a very quick overview of the different weights; for more information on each, follow the links below:

• Download weight: Calculated by determining how much bandwidth is required to download and view the object. Larger and more visually complex objects have a higher download weight. You can reduce the download weight of complex objects by generating or uploading less complex meshes for differing levels of detail when you upload a model.
• Physics weight: Calculated by determining the complexity of the object's physics model. You can reduce the complexity of a mesh's physics model by using the analysis and simplification tools in the Upload Model window, by uploading your own less-detailed physics model, or by choosing a different physics shape type, such as Convex Hull, on the Features tab of the Build Tools window. Vehicles must have a physics weight of 32 or lower, but may have higher download or server weights.
• Server weight: Measures the impact an object has on Second Life's server resources. Objects that are composed of many prims and have physics enabled and/or contain scripts tend to have high server weights.

In summary, the whole is greater than the sum of its parts, and sometimes in ways that are non-intuitive.

[Kwakkelde Kwak]

The meshes are the reason in a way, but they aren't in a way....

They are the reason, because when you link a sculpted or "normal"  prim to them, the landimpact, or primcost if you will, will be calculated as if they were meshes aswell. I suspect the physics weight of the cylinders is the reason for the increase. Edit your item and set the physics for the cylinders from "convex hull" to "none".

The meshes aren't the reason, because the weights for meshes are already calculated like Rolig discribed. It's possible to turn 2 meshes worth one prim each into a combined landimpact of 3, but just as likely into 1. That's because the three different weights are added up and then the highest will determine the overall weight.

Two identical meshes worth 0.6 will be 1.2 which is rounded to 1.

Two identical meshes worth 1.4 will be 2.8 which is rounded to 3.

[Rolig Loon]

To add to Kwakkelde's excellent explanation, let me point you to Innula Zenovka's very lucid discsussion in this recent thread >>> http://community.secondlife.com/t5/LSL-Scripting/Redoing-phantom-child-objects/td-p/1641681/page/2  .  Look at the latest of her posts.