by Leon Rosenshein

Natural Science

Wheels within wheels
In a spiral array
A pattern so grand and complex
Time after time
We lose sight of the way
Our causes can't see their effects

    -- Neil Peart

Software development is about patterns. Design patterns, data patterns, and execution patterns. Flow graphs, timing graphs, and relationship graphs. Project structure, team structure, and organizational patterns. All fitting together to make an even bigger pattern

We've all heard about the GOFs design patterns. We know when to use them and when not to. A couple of days ago I talked about branching patterns. Again, there are guidelines about when to use which pattern and when to avoid it.

But, the really interesting part is that those patterns scale just like everything else we do. And what makes the most sense locally might not be the right choice when looked at from a larger scale. Or maybe it does *now*, but won't later.

I've mentioned the Global Ortho program before. One of the things we did as part of it was color balancing and blending. We went through _lots_ of iterations, looking at seam lines between images and between flightlines. And we were able to do a really good job of making those lines disappear. So we rolled it out. And we found that while things looked really good up close, there were still abrupt changes across collection boundaries, image delivery boundaries, and processing unit boundaries. Eventually we realized that in addition to all of the local knowledge and optimizations we used for blending adjacent images into a mosaic we needed to bring in high level knowledge, in this case Blue Marble imagery to provide a top-down, globally consistent, artistically color balanced data to use in each mosaic so that they worked well not only individually, but with each other.

And that's our challenge as engineers. To see the big picture. To make the right tradeoffs between local and global optimizations. Between building for today and preparing for the future. To see the "wheels within wheels", the "pattern so grand and complex". Plus, I get to quote Neil Peart, RIP