1 | ;+ |
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2 | ; |
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3 | ; @file_comments |
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4 | ; Calculate a linear equation of the type ax+by+c=0 |
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5 | ; thanks to coordinates of 2 points. |
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6 | ; comment: we can have a table with pairs of points. |
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7 | ; |
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8 | ; @categories |
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9 | ; Utilities |
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10 | ; |
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11 | ; @param POINT1 {in}{required} |
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12 | ; This is the first point of (the) straight line(s) whose we want to calculate |
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13 | ; equation(s) |
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14 | ; |
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15 | ; @param POINT2 {in}{required} |
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16 | ; This is the second point of (the) straight line(s) whose we want to calculate |
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17 | ; equation(s) |
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18 | ; |
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19 | ; There is 2 possibilities: |
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20 | ; 1) point is a complex or a table of complex, where each element is the coordinates of the point. |
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21 | ; 2) point is a table of real of dimension 2,number_of_straight_line. |
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22 | ; For each row of the table, we have coordinates of the point. |
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23 | ; |
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24 | ; @returns |
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25 | ; abc is a table of dimension 3, number_of_straight_line, |
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26 | ; where for each line of the table we obtain the 3 parameters |
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27 | ; a, b and c of the linear equation ax+by+c=0 |
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28 | ; |
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29 | ; @examples |
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30 | ; IDL> abc=linearequation(complex(1,2),[3,4]) |
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31 | ; IDL> print, abc[0]*1+abc[1]*2+abc[2] |
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32 | ; 0.00000 |
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33 | ; |
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34 | ; @history |
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35 | ; Sebastien Masson (smasson\@lodyc.jussieu.fr) |
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36 | ; 10 juin 2000 |
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37 | ; |
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38 | ; @version |
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39 | ; $Id$ |
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40 | ; |
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41 | ;- |
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42 | FUNCTION linearequation, point1, point2 |
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43 | ; |
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44 | compile_opt idl2, strictarrsubs |
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45 | ; |
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46 | |
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47 | if size(point1, /type) EQ 6 OR size(point1, /type) EQ 9 then begin |
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48 | x1 = float(point1) |
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49 | y1 = imaginary(point1) |
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50 | ENDIF ELSE BEGIN |
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51 | x1 = float(reform(point1[0, *])) |
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52 | y1 = float(reform(point1[1, *])) |
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53 | ENDELSE |
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54 | |
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55 | if size(point2, /type) EQ 6 OR size(point2, /type) EQ 9 then begin |
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56 | x2 = float(point2) |
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57 | y2 = imaginary(point2) |
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58 | ENDIF ELSE BEGIN |
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59 | x2 = float(reform(point2[0, *])) |
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60 | y2 = float(reform(point2[1, *])) |
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61 | ENDELSE |
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62 | |
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63 | vertical = where(x1 EQ x2) |
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64 | novertical = where(x1 NE x2) |
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65 | abc = fltarr(3, n_elements(x1)) |
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66 | |
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67 | IF novertical[0] NE -1 then BEGIN |
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68 | ; y=mx+p |
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69 | nele = n_elements(novertical) |
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70 | m = (y2[novertical]-y1[novertical])/(x2[novertical]-x1[novertical]) |
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71 | p = (x2[novertical]*y1[novertical]-y2[novertical]*x1[novertical])/(x2[novertical]-x1[novertical]) |
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72 | abc[*, novertical] = [reform(-m, 1, nele), replicate(1, 1, nele), reform(-p, 1, nele)] |
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73 | ENDIF |
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74 | IF vertical[0] NE -1 then BEGIN |
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75 | ; x=ny+p |
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76 | nele = n_elements(vertical) |
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77 | n = (x2[vertical]-x1[vertical])/(y2[vertical]-y1[vertical]) |
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78 | p = (y2[vertical]*x1[vertical]-x2[vertical]*y1[vertical])/(y2[vertical]-y1[vertical]) |
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79 | abc[*, vertical] = [replicate(1, 1, nele), reform(-n, 1, nele), reform(-p, 1, nele)] |
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80 | ENDIF |
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81 | |
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82 | return, abc |
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83 | end |
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