- 18 - 
Junkins et al [37] use minor variations in this procedure. In the first 
step, polynomials of the third degree are used, the computation is performed for 
two sets of four points and the values of x' and y' obtained from the two sets are 
meaned. In the second step, a polynomial of the fifth degree is used. This 
polynomial has the required values of x' and y' at the end points and it fits at 
four discreet points. Killian and Meiss1 [40] use cubic spline curves, here also, 
without giving detailed formulas. 
The statement that the produced contour lines are smooth must be limited 
by the obvious requirement that the used s-distances of the discreet points in the 
second step be the same as those in the first step. The actual values of these 
distances are to some extent arbitrary. However, a different choice of distances 
leads to different values of x' and of y' and, therefore, of the tangents of the 
contour line at the discreet points. Presumably, but this should be more 
thoroughly checked, it makes little difference whether the used s-distances are 
equal to the chord lengths or equal to the actual lengths along the curves. 
0f interest would also be a comparison of contour lines obtained by 
parametric and by non-parametric functions. 
BIBLIOGRAPHY 
i. Reviews and comparisons 
  
[1] 1967. Bulletin No. 27, Société Frangaise de Photogrammetrie. Papers 
presented at the Symposium of the Inter-Commission Working Group on 
Highway Engineering of the ISP in Paris, June 1967. 
(1) Baussart, M., and Bonneval, H., La photographie aérienne dans les études 
d'autoroutes. 
Blaschke, W., Le modèle digital M.I.T. 
Nordin, H., La représentation digitale du terrain en vue de la mesure 
des profils en long et en travers pour les projets routiers. 
Viita, E., La mise au point, en Finlande, de la méthode par surfaces. 
Hallmén, B., La représentation Nordisk ADB du terrain. 
Deligny, J.L., La méthode du semis de points et les programmes français 
de calcul électronique des tracés. 
Intercommission Working Group V/IV of the ISP, Digital Terrain Model 
- à presentation of the practical application of some existing DTMs. 
International Archives of Photogrammetry, Vol. XVII, Part 2. 
(1) Williams, J., The Terra Model 
(2) Viita, E., The Finnish Model 
(3) Hallmén, B., The Nordisk ADB Model 
(4) Adolffson, B., The VV-DTM 
(5) Linkwitz, K., The DTM-Stuttgart. 
[3] 1970. Linkwitz, K., Digitale Geldndemodelle, BuL 38, 1.