GPSrChive Discussion Forum

When using my Oregon 750 in the CBD of Melbourne recently the streets displayed with kinks and twists in them. They should have been straight lines. Any thoughts please - the loaded maps is TOPO Australia & New Zealand v5 - a Garmin propriety product.

Would be very helpful if you could take screen captures to share next time it happens, without seeing any images etc., It is difficult to offer guidance.

As someone who makes maps in Garmin format commercially, I have experienced what you describe. I'll do my best to explain.

At the highest resolution level (zoomed in), Garmin maps can only display vector data at a certain resolution. If my raw vector data, say a line, has more nodes than the highest zoom level can display, the Garmin format will generalize or horizontally adjust these nodes to fit the defined resolution grid.

Let's say you have a long, straight road line. This line is better handled by Garmin maps by drawing it with only two nodes, a beginning and an end. If there are too many nodes, it is unlikely these nodes will fall on the precise XY resolution grid. Therefore, in processing, the code will move these nodes to fit the map resolution grid and, depending on the zoom level and node location, will appear to zig-zag.

When making my maps I always reduce the node count on new vector data that I import into the map. The zig-zag effect is virtually eliminated by doing this. With large datasets it becomes more difficult but many GIS software programs have some type of node reduction tool that can be applied to large datasets.

In short, you're seeing the "squiggly" lines because of the data used in the map. It's not a rendering error of the unit itself.

Hope that helps.
Cheers!