Here's a video showing the smooth zooming achieved with my OpenGL ES implementation. I also show how the Pixel Qi display turns reflective grayscale when the backlight is turned off. This should be readable in full sunlight.

I have a background thread that reads the compressed PNG tiles as required (and pre-caching tiles of higher and lower magnification). The PNG tiles are uncompressed as they are needed as textures for the map rendering.

My next steps are to fix the known bugs in the OpenGL rendering, then post the code to GitHub. Then I think I'll design the PCB for turning the Raspberry Pi on and off so that I can send the order off while I work on other things.

After that it is either getting the nRF51822 boards for the Bluetooth Low Enegy (BLE) communication from the GPS dongle to the plotter working, or starting to build the case.