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While testing contours generation in GroundTruth, I wanted to find out which values for the following cgpsmapper settings are optimal:

• TreSize
• SimplifyLevel
• PreProcess

SimplifyLevel

This setting specifies the simplification level for Douglas-Peucker simplification algorithm used by cgpsmapper. The value range is from 0.1 (maximum simplification) to 10 (no simplification). Of course, more the map features are simplified, the smaller the IMG file will be, but you loose data quality. After experimenting with this value, here are my conclusions:

• The simplification level does not affect the cgpsmapper’s speed of generating IMG files.
• There is no real noticeable difference in map quality between level 10 and 1.
• There is a noticeable difference in map quality between level 1 and 0.1 (see screenshots below).
• Total map sizes: 53 MB (level 10), 44 MB (level 1), 25 MB (level 0.1)

Conclusion: SimplifyLevel 1 seems to be the best compromise between the map size and its quality.

PreProcess

This setting specifies what kind of preprocessing of data will be done by cgpsmapper (generalizations, intersection detections…). I did not notice any real difference when using any one of possible options. The map size is the same, so is the generating speed and map quality.

Conclusion: I’ll leave this setting to be specified by the user.

TreSize

This one is hard – I don’t really know exactly what this setting is really all about. To quote cgpsmapper’s manual:

Maximum allowed region size. A higher value increases the allowable region size, but may decrease the map performance; a lower value may increase the map size.

As I stated in previous post, TreSize value of 4000 caused generation of certain map tiles to fail. The failed tiles contained a lot of contour data. So I lowered it to 2500 and then it worked without problems. When I tried TreSize of 1000, it generated a little bit larger map and took a little bit more time.

Conclusion: I think TreSize=2000 is the best compromise value.

Contours with SimplifyLevel value of 1:

Contours with SimplifyLevel value of 0.1. Notice how contour lines at the top of the map now have much sharper edges: