## 4 Simulation Experiment
### Experimental Results
#### 4.2.4 Comparison of Different Altimeter Deviation Algorithms under Fixed Switching Time  
Altimeters have important applications in some areas of life safety. According to reports, in 2009, Flight TK1951 was caused by the \"\(-\)8 feet (approximately \(-\)2.4 m)\" accident during the approach phase, which was a disaster that caused the aircraft to crash and die due to inaccurate altimeter readings [40]. Today, such accidents have occurred from time to time; it can be seen that in addition to the operation and control of the crew and air traffic controllers, the accuracy of the altimeter is also a key factor in reducing accidents, therefore, it is necessary for us to carry out qualitative and quantitative analysis on the navigation and positioning error of the algorithm under different altimeter deviations. To explore the impact of different altimeter errors on the navigation and positioning performance, we set the switching time as 5 s, and combined with the accuracy level of the actual altimeter, according to Table 3, we divide the accuracy of the altimeter into: no deviation, fixed deviation \(\pm\)5 m, and fixed deviation \(\pm\)20 m, and then experiment with these different altimeter scenarios. The results are shown in Figure 9. Here, we also include the standard LEO2 switching + INS navigation and positioning algorithm and the standard LEO2 switching + INS + altimeter navigation and positioning algorithm as a reference. From Figure 9, we can also obtain a similar law, that is: under the same altimeter deviation condition, the navigation and positioning performance of the INS + LEO2 switching navigation positioning algorithm based on adjacent orbits is also better than that of the INS + LEO2 switching navigation positioning algorithm under the same orbit. On the same type of orbit (such as the same or adjacent orbit), as the altimeter deviation increases, the navigation and positioning performance gradually deteriorates. To quantitatively analyze the differences in navigation and positioning under different altimeter scenarios, we have calculated the trajectory errors of the INS + LEO2 switching navigation and positioning algorithm with different altimeter deviations when the fixed switching time is 5 s. The results are shown in Figure 10.  
From Figure 10, we can find that under the condition that the altimeter has no deviation, the INS + LEO2 switching navigation and positioning algorithm under the same orbit and the adjacent orbit can reach good location service effects, and the effect under adjacent orbits is better, especially in terms of longitude and latitude performance. However, the difference between the two algorithms in terms of high performance is not large, which is not difficult to understand, since to some extent, when there are only two visible satellites, the difference between the same orbit and the adjacent orbit is not much, but the satellite velocity vectors of the two orbit types are different, and the addition of an altimeter, in the vertical direction, has a similar improvement effect on the INS + LEO2 switching algorithm under the two orbit types. There are similar conclusions in other altimeter deviation cases. It is worth mentioning that if we deduct the fixed height deviation of the navigation positioning algorithm with fixed altimeter deviation, the robustness of the corresponding algorithm is also very good. Taking height deviations of 5 and 20 m as examples, under the same orbit and adjacent orbit, after deducting the fixed deviation, the absolute value of the mean value of the height difference of the INS + LEO2 switching + altimeter 5 m deviation algorithm is about 0.03 m, and the absolute value of the mean height difference of the INS + LEO2 switching + altimeter 20 m deviation algorithm is about 0.2 m. This also requiresus to choose an altimeter with less deviation as much as possible in practical applications, to improve the accuracy of location services.