In the past few years catalogues of HII region positions and, occasionally, intensities have been published for many nearby galaxies. These catalogues contain a lot of information about the structure of the underlying galaxies. For example one can study the form and scalelength of the HII region radial profiles, give a measure of the dumpiness of their distribution, the extent of their concentration in the spiral arms or other substructures, etc. Further information can be obtained with the help of Fourier analysis. This involves first decomposing the observed distribution into components of a given angular periodicity. Then each component can be analysed into a superposition of logarithmic spirals. One can thus obtain the power in each angular periodicity, the pitch angle of the arms, their amplitude etc., and compare with other spiral tracers. Such studies are particularly interesting if done homogeneously for a sufficiently large sample, since this will give mean or "standard" values, as well as allow correlations with Hubble type, luminosity class, or environment, thus perhaps leading to a more quantitative classification of galaxies. Last but not least one could try confrontations with theoretical predictions.
Though several such studies have been made in the past, they were mostly applied to only a few galaxies, so that no general picture is so far available. Hodge (1982) reviewed the optical surveys of HII regions in external galaxies. Hodge (1975a, 1975b) also presented data for and discussed the HII regions in irregular and in interacting galaxies. Hodge (1969b, 1969c) and Hodge & Kennicutt (1983) examined the radial distribution of HII regions in the rectified planes of 27 and 37 galaxies respectively. Van den Bergh (1981) and Hodge (1983, 1987) discussed the distribution of HII region diameters. Studies of the HII regions in the individual galaxies NGC 300, NGC 628, NGC 1566, NGC 2997, NGC 3631, NGC 4321, NGC 5236 and NGC 6946 given by Deharveng et al. (1988), Boeshaar & Hodge (1977), Sersic & Calderon (1978), Comte & Duquennoy (1982), Hodge (1976), Kennicutt & Hodge (1976, 1980), Anderson et al. (1983), Rumstay & Kaufman (1983), Bonnarel et al. (1986). Kalnajs (1975) pioneered the use of Fourier analysis applying it to M31, and Considére & Athanassoula (1982) presented the results for the HII region distributions in M31, M33, M51 and NGC 2997. Unfortunately no global and homogeneous analysis has been made of these data. We will thus in this and subsequent papers undertake a homogeneous analysis of the material at our disposal. In this paper we will present the information on the deprojection parameters, i.e. position and inclination angles, a necessary first step for all the analyses described above. In the next papers we will study the radial distribution of the HII regions, apply the Fourier analysis to the galaxies in which the HII regions trace some spiral structure, and finally we will look for possible subclustering of the HII regions in the arms. We present the sample in Sect. 2, a brief summary of the mathematical analysis in Sect. 3 and discuss the various methods used for measuring position and inclination angles in Sect. 4. Notes on individual galaxies are given in Sect. 5, while the discussion of the main results of this paper is in Section 6.