Normally the two space rods are joined to one ball, whose centre then 
represents the mechanical model point. Where the base is smaller than 100mm, 
the rods can be joined to two balls SOmm apart. In that case, for levelling in 
® ,a bz screw has to be used. Many users will be glad that the handwheel for 
heights is replaced by a foot disc. The design of the gears of the height drum, 
and the construction of the suspension of the plate carriers, are not yet ideal. 
4 The Stereo Facet Plotter of OMI 
Strictly speaking this instrument should not be in the category of 
analogue instruments. It could be considered as a rectifier as well. Its aim is to 
transfer detail from a photograph to a map, so its applications will be mainly 
in the fields of photo-interpretation and map completion or renovation. Al- 
though it can be said that its principle is the same as that of the camera lucida 
(sketch-master) its construction and completeness makes this comparison re- 
mote. 
One of the most important characteristics of the instrument is its 
stereoscopic observation capacity. The photographs are observed by a stereo- 
scope with variable magnification from one to times ten. The stereoscope is of 
the scanning type: the photographs are not moved for scanning, the optical 
components are. By means of a semi-transparent mirror the operator sees the 
map sheet together with the stereoscopic image. The image of the map, which 
is always seen as if it were at 250mm, can be deformed to coincide with the 
boundaries of a facet of the terrain observed thorugh the stereoscope. These 
deformations are of a perspective and an affine nature. 
The instrument will certainly be valuable for map completion and 
revision, as well as for the transfer of interpretation data to maps. 
5 The EMPD-1 and 2 of Cartographic Engineering Ltd. 
(ref Ross, H.F. (1975), Design and Development of Instruments for Electron 
Microscope Photogrammetry Photogramm Record, Vol VIII no 46). 
These instruments are specially designed for photographs taken with 
a scanning electron microscope, though the EMPD-2 is also suitable for photo- 
graphs taken with a transmission electron microscope. We understand that the 
EMPD-2, also called Micro-Surfer, is the only one on the market. The photo- 
graphs, up to size 100 x 100mm, are mounted on plate carriers which can be 
rotated around 3609. The two plate carriers are mounted together on an X-Y