Archive for September, 2010
Large GPS Track Logs
I had the need to display GPS tracks in DeepEarth. GPS tracks can contain thousands of points. DeepEarth has three update modes called ElementUpdate, PanOnlyUpdate and TransformUpdate for showing features such as tracks:
- ElementUpdate recalculates the point positions on every map movement. This produces an accurate track display but gets slower as the number of points increases.
- PanOnlyUpdate recalculates point positions during panning and hides features while zooming. Not too useful for me and didn’t seem to show anything anyway.
- TransformUpdate draws the tracks to the map once then scales and pans the vector graphic in synchronization with the map. This makes it very fast. Sadly the scaling code is flawed. Lines disappear as you zoom in and sections of the tracks become distorted, almost looking like calligraphy.
I wasted many evenings trying to get the scaling in TransformUpdate mode working before giving up. I then turned my attention back to the ElementUpdate mode to see where the bottleneck is. More >