vb.net - How to correctly draw to map coordinates in gdi+ -

i have large scanned map want use in order display location of moving target

i load map picture box inside panel

• the panel set auto-scroll. picture box size mode set auto_size

in order calculate transformation let user sample 3 points calculate affine transformation matrix

 [x' y' 1] = [x y 1] * [a b 0                         c d 0                         e f 1] 

i know transformation successful because mouse hover event displays correct coordinates:

private sub picmap_mousemove(byval sender object, byval e system.windows.forms.mouseeventargs) handles picmap.mousemove             if _calibsuccess                  dim curpoint(0) pointf                 curpoint(0).x = e.x : curpoint(0).y = e.y                  dim genericgraphics drawing.graphics = creategraphics()                 dim mat drawing2d.matrix = new drawing2d.matrix(mdlglobal._georefparams(0), mdlglobal._georefparams(3), _                                                                    mdlglobal._georefparams(1), mdlglobal._georefparams(4), _                                                                    mdlglobal._georefparams(2), mdlglobal._georefparams(5))                 genericgraphics.transform = mat                 genericgraphics.transformpoints(drawing2d.coordinatespace.device, drawing2d.coordinatespace.world, curpoint)                  lblx.text = curpoint(0).x                 lbly.text = curpoint(0).y             else                 lblx.text = e.x                 lbly.text = e.y             end if          end sub 

but when try draw marker on screen nothing

private sub picmap_paint(byval sender object, byval e system.windows.forms.painteventargs) handles picmap.paint         dim drawgraphics graphics = e.graphics           if _calibsuccess , _broadcasting             dim mat drawing2d.matrix = new drawing2d.matrix(mdlglobal._georefparams(0), mdlglobal._georefparams(3), _                                                                mdlglobal._georefparams(1), mdlglobal._georefparams(4), _                                                                mdlglobal._georefparams(2), mdlglobal._georefparams(5))             drawgraphics.resettransform()             drawgraphics.transform = mat              drawgraphics.fillrectangle(brushes.red, _shipbase.x - (100.0f / 3600.0f), _shipbase.y - (100.0f / 3600.0f), (200.0f / 3600.0f), (200.0f / 3600.0f))          end if     end sub 

could tell me doing wrong?

your transform matrix inverse of needs be. can tell because transformpoints call going world device coordinates, mouse input in device coordinates.