1 | ;------------------------------------------------------------ |
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2 | ;------------------------------------------------------------ |
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3 | ;------------------------------------------------------------ |
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4 | ;+ |
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5 | ; |
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6 | ; @file_comments |
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7 | ; Calculate coordinates of the intersection between 2 straight lines |
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8 | ; or of a succession of 2 straight lines. |
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9 | ; |
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10 | ; @categories utilities |
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11 | ; |
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12 | ; @param abc1 {in}{required} is the first table of dimension 3, number_of_pairs_of_straight_lines, |
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13 | ; whose each line contain the 3 parameters a,b and c of the first linear |
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14 | ; equation of the type ax+by+c=0 |
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15 | ; |
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16 | ; @param abc2 {in}{required} is second table of dimension 3, number_of_pairs_of_straight_lines, |
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17 | ; whose each line contain the 3 parameters a,b and c of the second linear |
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18 | ; equation of the type ax+by+c=0 |
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19 | ; |
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20 | ; @keyword FLOAT To return the output as a table of real numbers instead of vectors of complex (by default) |
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21 | ; |
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22 | ; @returns 2 possibilities: |
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23 | ; 1) by default: it is a vector of complex whose each element is the coordinates |
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24 | ; of the intersection point of a pair of straight lines. |
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25 | ; 2) if FLOAT is activated, it is a table of reals of dimension 2, |
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26 | ; number_of_pairs_of_straight_lines whose each row is the coordinates |
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27 | ; of the intersection point of a pair of straight line. |
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28 | ; |
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29 | ; @restrictions If the 2 straight line are parallel, we return coordinates (!values.f_nan,!values.f_nan) |
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30 | ; |
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31 | ; @restrictions Beware of the precision of the machine which make |
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32 | ; that calculated coordinates may not exactly verify |
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33 | ; equations of the pair of straight lines. |
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34 | ; |
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35 | ; @examples IDL> abc1=linearequation(complex(1,2),[3,4]) |
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36 | ; IDL> abc2=linearequation(complex(1,2),[8,15]) |
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37 | ; IDL> print, lineintersection(abc1, abc2) |
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38 | ; ( 1.00000, 2.00000) |
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39 | ; IDL> print, lineintersection(abc1, abc2,/float) |
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40 | ; 1.00000 2.00000 |
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41 | ; |
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42 | ; @history Sebastien Masson (smasson@lodyc.jussieu.fr) |
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43 | ; 10 juin 2000 |
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44 | ; |
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45 | ; @version $Id$ |
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46 | ; |
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47 | ;- |
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48 | ;------------------------------------------------------------ |
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49 | ;------------------------------------------------------------ |
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50 | ;------------------------------------------------------------ |
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51 | FUNCTION lineintersection, abc1, abc2, FLOAT = float |
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52 | ; |
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53 | ; |
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54 | compile_opt idl2, strictarrsubs |
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55 | ; |
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56 | a1 = float(reform(abc1[0, *])) |
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57 | b1 = float(reform(abc1[1, *])) |
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58 | c1 = float(reform(abc1[2, *])) |
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59 | a2 = float(reform(abc2[0, *])) |
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60 | b2 = float(reform(abc2[1, *])) |
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61 | c2 = float(reform(abc2[2, *])) |
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62 | ; |
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63 | determinant = a1*b2-a2*b1 |
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64 | nan = where(determinant EQ 0) |
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65 | if nan[0] NE -1 THEN determinant = !values.f_nan |
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66 | ; |
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67 | x = (b1*c2-c1*b2)/determinant |
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68 | y = (c1*a2-a1*c2)/determinant |
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69 | ; |
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70 | if keyword_set(float) then begin |
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71 | npts = n_elements(x) |
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72 | res = [reform(x, 1, npts, /over), reform(y, 1, npts, /over)] |
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73 | ENDIF ELSE res = complex(x, y) |
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74 | return, res |
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75 | end |
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