Comments on: Book Review: 3D Engine Design for Virtual Globes

By: xcbb

xcbb — Sat, 27 Aug 2011 11:50:23 +0000

Celestia is Open Source.

By: xcbb

xcbb — Sat, 27 Aug 2011 11:49:57 +0000

Or another piece of example code would be Celestia. It really has found a good approach to the range thing.

By: Patrick Cozzi

Patrick Cozzi — Thu, 04 Aug 2011 13:00:32 +0000

Leith, we did not use any OpenGL 4 features. I started the engine in late 2009. I was using OpenGL 3.1 at the time. Later, I upgraded the engine to GL 3.3 to use separate sampler objects. GL 4 and tessellation shaders came out while we were mid-stride so we weren’t able to include them.

Off the top of my head, I think tessellation shaders have limited use for rendering real terrain datasets. However, they are great for synthesizing detail after your highest resolution terrain, or perhaps while you wait for the next highest resolution terrain to page in.

You may be interested in our example code (http://www.virtualglobebook.com/code.html) which includes a terrain engine using geometry clipmapping.

By: Leith Bade

Leith Bade — Thu, 04 Aug 2011 06:20:04 +0000

Also quick question: is there any use of OpenGL 4 tessellation to accelerate the DEM mesh rendering?

By: Leith Bade

Leith Bade — Thu, 04 Aug 2011 06:18:45 +0000

I am seriously considering purchasing this book (or putting in a request for our university library to order it).

There are some really cool public domain high resolution DEMs and aerial photography for parts of New Zealand that I have always wanted to convert into a cool demo.

Also my current project on modelling cell phone networks would look really cool overlaid onto a 3D map…

By: Patrick Cozzi

Patrick Cozzi — Wed, 03 Aug 2011 15:52:32 +0000

Yeap, exactly Aleksandar.

By: Aleksandar

Aleksandar — Wed, 03 Aug 2011 14:34:51 +0000

Thanks Patrick!
This link is (also) available from your blog-site. 🙂
That article was posted on July 3rd, 2007, and even then avi said that:
“Big Caveat: the Google Earth code base has probably been rewritten several times since I was involved with Keyhole and perhaps even after these patents were submitted. Suffice it to say, the latest implementations may have changed significantly. And even my explanations are going to be so broad (and potentially out-dated) that no one should use this article as the basis for anything except intellectual curiosity and understanding.”

Please, don’t misunderstand what I wrote. I just wanted to say that the book is not about Google Earth, but gives very comprehensive overview of techniques used to implement virtual globes.

By: Patrick Cozzi

Patrick Cozzi — Wed, 03 Aug 2011 12:46:34 +0000

This article, How Google Earth [Really] Works may be interesting to some.

By: Aleksandar

Aleksandar — Wed, 03 Aug 2011 12:41:09 +0000

Well, you won’t learn how Google Earth works exactly. The book gives an overview of some state-of-the-art algorithms, but the implementation of Google Earth is still (and probably will be) a proprietary. If I remember correctly, Rage uses some kind of ray-casting for terrain rendering…

By: Patrick Cozzi

Patrick Cozzi — Wed, 03 Aug 2011 12:39:52 +0000

Leith, id’s MegaTextures are similar to what is used for high resolution imagery in virtual globes, except MegaTextures are much more general and work with arbitrary surfaces AFAIK. In virtual globes, we usually have a really big image that we want to wrap around an ellipsoid (or sphere) with displacements for terrain. The image is recursively divided into four, quad-tree style and streamed using out-of-core rendering. id also has some interesting work where they minimize seek times for streaming from hard drives and DVDs. I’m not sure if any virtual globes are doing this, but virtual globes usually rely on beefy back-end technology to meet the bandwidth requirements.

Patrick

By: Aleksandar

Aleksandar — Wed, 03 Aug 2011 12:33:04 +0000

The book is really great!

This is the first book of that kind. It covers all important aspects of large terrain rendering and presents excellent foundation for further research.
The full source code is also available for download.

But I don’t understand why did you have to take photos of the pages when TOC and some of the chapters can be downloaded from the site:
http://www.virtualglobebook.com/index.html
? 🙂

By: Leith Bade

Leith Bade — Wed, 03 Aug 2011 12:24:02 +0000

Cool! I have always wanted to know how Google Earth works…

I wonder if id Software’s Rage uses similar technology to render the high resolution virtual textures in the game.