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1、IS0 8721 INTERNATIONAL STANDARD First edition 1987-10-15 INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXAYHAPOAHAR OPAHM3AL this evaluation shall be repeated whenever the system is modified to an extent which could cause a change in accuracy. 4.1 Disto
2、rtion index The distortion index shall be assessed using the photographic target and procedure described respectively in A. 1.1 and A. 1.2 of the annex. It shall be evaluated as indicated in A.1.3. The distortion index shall not exceed 1 %. 4.2 Time base A time base is required. It shall permit dete
3、rmination of the time between recorded events to an accuracy of the reciprocal of the imaging rate or 1 % of the actual time, whichever is greater. 4.3 Time origin identification device The accuracy of the device shall be equal to the reciprocal of the imaging rate. 4.4 Imaging rate The imaging rate
4、 shall be left to the users discretion, taking ac- count of all factors including : - the goal to be attained: - the limitations due to the equipment (e.g. blur); - the need to combine data from several image-taking devices and from electronic recordings of the impact test. The users choice shall be
5、 guided by the distance the recorded point moves between two images analysed. This distance shall not exceed any accuracy requirement there may be on deter- mination of position. 4.5 Reference length A length calibration shall be carried out which permits deter- mination of lengths within any requir
6、ements there may be on accuracy. In the absence of such requirements, it is recommended that determinations of length to within f 1 % of the diagonal of the picture should be possible. 1) The influence of the operator on accuracy has not been taken into account during the development of this Interna
7、tional Standard. IS0 9721 : 1997 (E) Annex Distortion index measurement methods (This annex forms an integral part of the Standard.) A.1 Standard target method A.l.l Test target A rectangular target of type and dimensions in conformity with the figure shall be used. This target shall be divided into
8、 four parts by joining the centre points of the two opposite sides. In each quadrant thus ob- tained, and at the target centre, circles 400 IL 1 mm in dia- meter shall be drawn. The five circles shall be marked on their circumferences with 16 reference marks, this defining eight diameters for each,
9、and hence 46 diameters for the whole target. A.1.2 Test method The target shall be recorded full-frame by the image-taking device which forms one element of the optical data channel to be tested. The image-recording medium to be used for calibration shall be of the same type and quality as those use
10、d for impact testing. It shall be analysed using the analysis system. The coordinates of the marks of each diameter di shall be measured on the same frame while the coordinates of the marks of different diameters shall be measured on consecutive analysed images. A.1.3 Calculation of results The 46 d
11、iameters di shall be calculated between two points, P and Q, from the equation d, = (xp - x(-J* + (yp - yaPI Ot5 The diameter, & and the standard deviation, S, respectively shall be calculated taking the 40 diameter values dj into account from the following equations : N c di i= 1 d=T- where N = 46
12、N c (d, - d)* Of5 i= 1 .Y= N- 1 where N - 1 = 39 The distortion index is equal to the ratio of the standard devia- tion, s, to the mean diameter, d, i.e. s d A.2 Alternative (indirect) method Other targets with different sizes or patterns of reference marks may be used, in which case the user shall
13、determine the distor- tion index indirectly. There is then also a need to show that the indirect method gives results equivalent to those using the target specified in A. 1.1. This may be of advantage when for instance a target with a rec- tangular pattern of reference marks is used for the determin
14、a- tion of lens corrections, which are needed in case of some wide-angle lenses. IS0 8721 : 1987 (E) Dimensions in millimetres - t = 1 05025 Figure - Target for distortion index determination IS0 8721 : 1987 IFI CDU 629.11 : 981.7 : 620.178.7 Descripteurs : vbhicule routier, essai, essai au choc, materiel dessai, matbrie doptique, spkification. Prix base sur 3 pages -,-,-