The scaleheight of a galactic disk is certainly a very
important attribute of a spiral galaxy.
There are two well-known approaches to estimate the parameter.
The one suggested
by van der Kruit & Searle (1981, 1982) is for edge-on
spirals. The other one is for non-edge-on spiral galaxies,
which are the majority of spirals, proposed by Peng (1988).
The latter is useful and
rather simple as long as spiral arms
are distinguishable on their images. As a test for his method, Peng measured
the
scaleheights of four spiral galaxies
(NGC 628 (M 74), NGC 5236 (M 83), NGC 5194 (M 51),
and UGC 2885).
The main points of Peng's method (1988) in present paper are:
1. Changing the grey-scale of the image of a galaxy, finding the position of
the innermost point of the spiral
arm and measuring its coordinates (
) from the galactic center,
2. Assuming different inclinations (
, i.e. the angle between
the galactic plane and the tangent plane) near the
value of 
) and fitting the spiral arm
starting from that innermost point with
a logarithmic spiral curve to get its wounding parameter (
),
3. Determining the optimum inclination and the corresponding wounding
parameter by comparing the fitted spiral arm with the image.
Figure 11 (click here) gives an example how to use Peng's method, we fit NGC 1096
with the optimum inclination (
) and wounding
parameters (
and 
, corresponding to two
arms),
4. The scaleheight of the galactic disk, h in arc-minute,
may be calculated by
where m is the number of the arms.
5. The scaleheight of the galactic disk, H in kpc, is
here d is the distance of the galaxy from the Galactic Center,
where H0 is the Hubble constant taken as
75 km/s/Mpc, 
, taken from the Third Catalog
of Bright Galaxies by de Vaucouleurs et al. (1991, RC3),
the weighted mean radial velocity of the radio and optical
redshifts of the galaxy corrected to the Galactic Center.
This paper presents our estimation of scaleheights
for 486 southern spiral galaxies selected from more than 1500 ones
whose images are taken from the Digitized Sky Survey.
All these galaxies are the grand design spiral ones with
Arm Classification 
(Elmegreen & Elmegreen 1987).
Since there are usually
two arms in a galaxy, the arm with the minimum 
is picked up
for measuring the scaleheight.
Our data reduction and analyses were done on the Sun Workstation installed with IRAF software.