1 | FUNCTION distance_rad (lon1, lat1, lon2, lat2) |
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2 | !**** |
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3 | ! ***************************** |
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4 | ! * OASIS ROUTINE - LEVEL ? * |
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5 | ! * ------------- ------- * |
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6 | ! ***************************** |
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7 | ! |
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8 | !**** *distance* - calculate the distance between two points on a sphere |
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9 | ! |
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10 | ! Purpose: |
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11 | ! ------- |
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12 | ! Calculation of the distance between two points on a sphere |
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13 | ! 1. Transformation to x,y,z-coordinates |
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14 | ! 2. Calculating the distance |
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15 | ! 3. Calculating the distance on the sphere |
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16 | ! |
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17 | !** Interface: |
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18 | ! --------- |
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19 | ! *CALL* *distance_rad*(lon1, lat1, lon2, lat2) |
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20 | ! |
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21 | ! Input: |
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22 | ! ----- |
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23 | ! lon1 : longitude of first point (rad) |
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24 | ! lat1 : latitude of first point (rad) |
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25 | ! lon2 : longitude of second point (rad) |
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26 | ! lat2 : latitude of second point (rad) |
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27 | ! |
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28 | ! Output: |
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29 | ! ------ |
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30 | ! distance : distance |
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31 | !! |
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32 | ! History: |
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33 | ! ------- |
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34 | ! Version Programmer Date Description |
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35 | ! ------- ---------- ---- ----------- |
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36 | ! 2.5 V. Gayler 2001/09/20 created |
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37 | ! |
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38 | !----------------------------------------------------------------------- |
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39 | USE mod_oasis |
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40 | |
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41 | IMPLICIT NONE |
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42 | !----------------------------------------------------------------------- |
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43 | ! INTENT(IN) |
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44 | !----------------------------------------------------------------------- |
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45 | REAL (kind=ip_double_p), INTENT(IN) :: lon1, & ! longitude of first point (rad) |
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46 | lon2, & ! longitude of second point (rad) |
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47 | lat1, & ! latitude of first point (rad) |
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48 | lat2 ! latitude of second point (rad) |
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49 | |
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50 | !----------------------------------------------------------------------- |
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51 | ! LOCAL VARIABLES |
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52 | !----------------------------------------------------------------------- |
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53 | REAL (kind=ip_double_p) :: x1, y1, z1, & ! coordinates of the first point |
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54 | x2, y2, z2, & ! coordinates of the second point |
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55 | distance_rad ! distance between the points (rad) |
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56 | |
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57 | !----------------------------------------------------------------------- |
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58 | |
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59 | ! Transformation to x,y,z-coordinates |
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60 | ! ----------------------------------- |
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61 | x1 = cos(lat1)*cos(lon1) |
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62 | y1 = cos(lat1)*sin(lon1) |
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63 | z1 = sin(lat1) |
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64 | |
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65 | x2 = cos(lat2)*cos(lon2) |
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66 | y2 = cos(lat2)*sin(lon2) |
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67 | z2 = sin(lat2) |
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68 | |
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69 | ! Calculation of the distance |
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70 | ! --------------------------- |
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71 | ! direct distance: |
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72 | distance_rad = SQRT((x2-x1)**2 + (y2-y1)**2 + (z2-z1)**2) |
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73 | |
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74 | ! distance along the surface: |
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75 | distance_rad= 2.d0*ASIN(distance_rad/2.d0) |
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76 | |
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77 | !----------------------------------------------------------------------- |
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78 | RETURN |
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79 | END FUNCTION distance_rad |
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80 | |
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