Bitmaps problem

Hello, dear colleagues!
I’m a user of Opencascade from Russia. My company develops municipal GIS. I want to use Opencascade 4.0 as a graphical kernel. In terms of this case I need to clarify some questions.
Testing application “Sample2Dimage” allows to insert raster images like bmp, gif, etc. In this case sizes of the inserted fragment don’t coincide with the origin. I use graphical map-cases with size 500*500 mm. When I insert a raster its sizes are distorted till 1846*1846 mm. Why is it so? How can I solve this problem?
Yours faithfully, Alex Safonov