AnalyticalGraphicsInc/cesium — pull request #192 by mramato (2012-08-29 17:17:21+00:00)
Title: Fix issue #187

As per our discussion of issue #187, billboards now default construct with an `index` of `-1`. `-1` in this case, is the magic number signifying "no image". If an image index is set but not present in the texture atlas, an exception is thrown. I also updated example code and tests.