Mesh and data streaming from SL to client

[Dain Shan]

Hi everyone

 

Lately i being confronted with a lot of questions about mesh.

One of them is, how much more data has to be downloaded from a sim with mesh.

Somehow i get the expression that peaople assume that the upload data size is also the download size of a file, but i know for aure that this is not the case. The download size is definately smaller.

I know the question is a bit vague as there are serval variables that influences this. But is there a general rule of thumb maybe, or soemthing that might point in the right direction?

Many thanks in advance

[Jenni Darkwatch]

You can look at the cache dir. Downloaded mesh objects are stored there, so you have the size.

[Drongle McMahon]

"The download size is definately smaller."

You may be confusing the size of the collada file with the upload data size. The collada (dae) file is not uploaded to the server. It is converted by the viewer into a much more space-efficient internal format, and then compressed, before it is sent to the server. As far as I know, the download format is exactly the same as the upload format, and if all the data is fetched, it would be the same size. However, the viewer will not request the higher LOD data unless it needs it. So, as long as your camera is not close enough to see the highest LOD, then the download data size will indeed be smaller than the upload data that contains all the LODs.

[Dain Shan]

Thanks Drongle and Jenni

 

Thats really helpful.

The problem is, that some people with a slower DSL connection seem to have issues with rez times if there are many mesh obejcts around. I can not verify that, So i came to the idea that maybe the pure size of the downloaded files might have been the cause of that.

The person whos hit the hardest have an connection that is called "DSL - Light" here. That equals a 384kbit connection at max.
 

I will test that a bit more to see if we have the cause here.

[Drongle McMahon]

The download weight, which usually becomes the land impact, is calculated from the actual size of the download data after compression. It also includes adjustment for how often the higher LODs have to be downloaded and how often only the lower ones. So it is a pretty good indication of the relative amount of data the mesh needs to be downloaded, although in reality that depends heavily on the actual graphics settings - higher object detail (renderVolumeLODFactor) and greater draw distance mean more data to be downloaded. You can see the download weight by selecting, choosing edit, and clicking on the 'more info' link on the Object tab of the edit dialog. Unfortunately, many mesh items are not well optimised and have excessive download weights. This is especially true of attachments where there is no land impact cost as incentive to optimise. Many mesh also use several large baked textures, and the texture download can take more data than the geometry download. That is not included in the land impact.