Background reflexion on reflective materials

Hi, its been a while since my last post but I came upon a new issue.

I have a background image that I was using for a while now but since we now do windows with a reflective material, whe usual background image used as flat background doesn't reflect on the front on the reflection.

I tried cylindrical and sphere but it scraps the background image as it strech it.

On the attached image, we have the grass on 1st floor, water on the 2nd floor windows but on 3rd and 4th floor, where the sky should be, there is nothing, just the plain sketchup gray color.

Thanks for the fast reply.

[Edit - added image directly to post - using icons above the edit area - Al Hart]

Attachments:

window issue.png, 2 MB

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Permalink Reply by Render Plus on June 7, 2011 at 8:40am

Background images to not reflect at all.

In order to get the effect you want, you need to use an HDRi image. These are full 360 degree images which reflect properly from all directions.

There are a few included with IRender nXt (use the + icon on the HDRi setup tab to see them), and more are available on this link: HDRi Skies

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Permalink Reply by Simon Loisel-Goudreau on June 7, 2011 at 11:25am

I understand the HDRI background but when doing a 5000x2564 render, if my judgement is right about the explication on HDRi skies, won't be good because the panoramic image simply isn't big enough.

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Permalink Reply by Render Plus on June 7, 2011 at 11:41am

Even in the image you posted, the background does not look like it was a 5000 pixel wide image.

The HDRi sky needs to have resolution equal to 50% to 100% of the resolution of the rendered image.

If your Rendered image is 5000 pixels wide, and you use a 60 degree Field of View. (The default for SketchUp is only 35 degrees), then the HDRi image will have to be 6 X 5000 pixels wide - 30,000.

For this particular scene, with all the windows facing in the same direction, you could place a SketchUp image in front of the building, but not visible in the scene, to be the reflected sky. If the image is not bright enough, you can add some "Self Glow" to it.

This won't work nearly as well with curved reflective surfaces, of with reflections going in more than 1 or 2 directions - e.g. side windows, wky lights, etc.

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Permalink Reply by Simon Loisel-Goudreau on June 7, 2011 at 11:51am

Wouldn't the surface we create like that affect the main model with shadow?

And of course the image i posted isn't 5000 pixels wide, it was actually just a print from the main image to show the area of the problem.

I don't know if the was to use HDRi background have changed from here: http://www.renderplus.com/wk/HDRi_Skies_w.htm

but I can't get it to work.

I'm getting the exterior preset and turning sun off then HDMi on and no background actually appears.

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Permalink Reply by Render Plus on June 7, 2011 at 12:05pm

You could place the image way, way behind the camera, and unless the sun was shining through the image, it should not effect lighting too much. Of couse, one of the advantages of HDRi is that is can be user for illumination as well as reflection.

I'm getting the exterior preset and turning sun off then HDMi on and no background actually appears.

You have turn the sky on, (on the presets tab or on the sky tab), in order to see the HDRi background. Otherwise the HDRi is only used for lighting effect.

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Permalink Reply by Simon Loisel-Goudreau on June 7, 2011 at 12:12pm

If I put the image way back, its smaller and its a trial and error to find the best position to put image at, which, at 1 hours a render, I don't have the time to do that. If I make the image bigger, there is more chances that it will be in the way of the sun.

For the HDRi sky, it does work but my model turns completely black.

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Permalink Reply by Render Plus on June 7, 2011 at 12:19pm

We don't really recommend the fake image solution - because of the problems you have seen. And, of course, you would have to move the fake image every thime you chose a new view.

You can greatly improve the testing phase by rendering to a much smaller size (400 pixels or 600 pixels) while setting the fake image, and by rendering just the windows and image. (You can use layers for this, or there is a right click to render just the selected items - you can select the image and the windows and render just them.

HDRi skies do work. You just have to get the settings right. If you are still having problems, send your model to support@renderplus.com and we will take a look. (If you can remove everything except the building with the wandows and the HDRi settings, it will make things easier for us.)

Here is a sample HDRi rendering I just created:

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Permalink Reply by Simon Loisel-Goudreau on June 7, 2011 at 12:27pm

I will send the image with the upload option since it seems a couple windows and a part of terrain are almost 20mo.

What I actually need is and HDRi of a sky and thats it, a couple clouds and i'm good to go.

If you can help me on that within the hour it would save my life and my boss too.

I'm trying to finish both renders for our presentation tomorrow and since the other one is just a top parralel view and doesn't need any skies, its the only one i have left to do.

I'm rendering at 5000x2564 on the main model and the one i'll send is just a couple blocs i've placed about where they should be. (called HDRi problems) I don't know if you can get sun settings with HDRi setting since there should be shadows on the model too?

I'll be sending you my work email through your private message box in a couple minutes so it's easier to contact me.

Thanks

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Permalink Reply by Render Plus on June 7, 2011 at 12:34pm

Zip everything up. Our email program can handle 30MB attachments with no problem.

If you do have a problem, use the Upload tab at the top of this web page.

In order to get things done my tomorrow, you may want to place the reflected sky, etc. as a texture/material to the windows. (I forgot to mention that as another solution.) Or you may want to place the sky relflections after rendering with a Paint Program.

You can also send your email, or anything else to support@renderplus.com that works much better for use than the private email on the forum, and it gets saved in our email system, so it is easier to find and use.

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Permalink Reply by Simon Loisel-Goudreau on June 7, 2011 at 12:38pm

Its actually too late for that, the file is already uploaded and the email sent to your mail box, i'll be cheking forums every 5-10 minutes anyway.

I was wondering, with the change the window tecture for the sky idea, is the reflection for everything else (balcony, bush, plants and flowers) will be affected?

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Permalink Reply by Render Plus on June 7, 2011 at 12:45pm

You would only apply the fake reflection to the top two rows of windows.

However, if there was a tree reflected in a window, you should be able to place a sky-texture on the window and make it 50% reflective as well and you would see some of the tree as well.

None of these 'fake" solutions are great. The HDRi is the right answer.

One thing about the reflective texture is that you can see what it will look like from SketchUp.

Another "trick" to make it work, is to render the model from the other side of the wall, with the windows transparent. This rendering will show what you would see through the windows. (All of this is a lot of work - this "trick" here is a way to add reflections directly to SketchUp - by viewing the model from the other side, grabbing the images seen through the windows - reversing them and them placing them on the windows.

But I think it will be easier to add the sky reflections using a paint program if time is a problem.