[segway] observation

Based on the following table, maybe we want to use different gaussian models depending on how the far the ball is.

	obs-mean	obs-cov
0.79	0.7953 0.2288	1.0e-004 * 0.0084 0.0197 0.0197 0.1291
1.22	1.2227 0.2958	1.0e-004 * 0.1019 0.0393 0.0393 0.0191
1.52	1.5191 0.3285	1.0e-004 * 0.3333 0.1009 0.1009 0.0408
1.94	1.9478 0.3875	1.0e-003 * 0.1108 0.0323 0.0323 0.0106
2.21	2.2319 0.3525	1.0e-003 * 0.0914 0.0817 0.0817 0.1286
2.64	2.2310 0.3525	1.0e-003 * 0.1015 0.0869 0.0869 0.1430
2.81	2.7739 0.4569	1.0e-003 * 0.8690 0.1797 0.1797 0.0383
4.12	4.1177 -0.0114	1.0e-003 * 4.2677 0.0231 0.0231 0.0090