Huge difference in rendering times just by rotating around it?

[AcesHigh]

I simply cant understand. I have this house that I rendered a front view in like 30 minutes - 1 hour...

then I rotated around it to render the back of the house... its 4 hours and still a LOOONG way to go! What can be the reason for this?

[andybot_cg]

Re: Huge difference in rendering times just by rotating around it?

are you using displacement? If there is a larger area of displacement material in your view, it can take much longer to render.

[arqestevez1]

Re: Huge difference in rendering times just by rotating around it?

not only displacements... two sided materials, semi traslucent materials... or if you're using smart trees, materials with transperancy bitmaps also increase render times

[AcesHigh]

Re: Huge difference in rendering times just by rotating around it?

yes, I am using displacement, but the area which appears is about the same in both views. Maybe the camera is a bit closer to the ground (its grass displacement) in the one that takes longer to render, but really... its the whole image which takes longer to render, not only the grass area.


edit: its possible the displacement was the cause. I modified edge lenght from 3 to 4 and raised a camera like 50 cm only... and it rendered normal... really, I am not sure if I got better results from modifying the edge lenght or raising the camera.

But its quite funny that it rendered normal time now. Before, when it was rendering a palm tree in the backyear, it would take over one minute for each bracket to render a small square of the image, on the final pass, over the palm tree foliage. Now, it took like one second for each bracket to move on, render another square, move on, etc!!

But the palm tree has no displacement or anything like that! I would expect the displacement to influence rendering times over the grass area, not over the ENTIRE scene!

[AcesHigh]

Re: Huge difference in rendering times just by rotating around it?

I am using a Quadcore Q9300... do you guys think an I7 920 would help with VRAY for Sketchup?

[andybot_cg]

Re: Huge difference in rendering times just by rotating around it?

Yeah, I've run into the same thing, which is why I mentioned it. I have no idea why, but sometimes when I am close to a displaced material, the render will just bog down and take forever, as soon as I adjust the view, it is back to normal. I wonder if it has to do with the geometry that vray is generating for displacement - there must be some threshold over which it creates a lot more of it.

more processors=faster render times! I have a 6 core AMD at 3Ghz (overclocked), and it's awesome! I used to run my renders on a dual core PC, and it took forever.

[AcesHigh]

Re: Huge difference in rendering times just by rotating around it?

Yeah, I've run into the same thing, which is why I mentioned it. I have no idea why, but sometimes when I am close to a displaced material, the render will just bog down and take forever

hmmm... I am guessing this may be something to do with that checkbox stuff about displacement being relative to world units or to the viewport.

can some moderator elucidate our questions on this topic and explain it better? Thanks

[fpedrogo]

Re: Huge difference in rendering times just by rotating around it?

When you are using displacement you have to keep in mind these concepts. The "edge length" basically tell V-Ray the length in pixel of the triangle mesh edge. If the edge is bigger that this value, V-Ray will subdivide the edge until you have the same dimension that you specified. If you are using "View dependent" the edge depend of the image pixel size, and how close or away the displacement materials are from the camera is very important. For example if you setup the "Edge Length" to 4.0, V-ray will subdivide the edges until they meet the 4 pixels long in the images. The good thing about "View dependent" is that the object further away from the camera are going to have less subdivision that the object closer to the camera and you are not going to see any difference in quality. Thus you are going to have a faster render.
If "View dependent" is off, the edges will be calculate in world units, meaning that every single edge are going to have the same amount of subdivision. So the object further away from the camera are going to have the same amount of subdivision that the object closer to the camera. The result is that you are going to use more memory of ram and more render time.
You don't have to worry about use a large number of "Max Subdivision". The default is Ok in almost all the cases (the real value is actually the square on that number). Once V-Ray have reached the correct amount of edge length, V-ray is going to stop the subdivision and probably you are going to use less that 256 subdivision. I recommend you subdivide the actual geometry in SU and don't use a large "Max Subdivision".

In overview, If the displacement is closer to the camera you are going to have more subdivision, because the displacement is view dependent. So object closer are going to be more subdivided. So, if you get closer to the camera just increase the "edge length" to reduce the triangle subdivision.

I hope this help.

[AcesHigh]

Re: Huge difference in rendering times just by rotating around it?

it definitly helps.