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Hi Sankhesh and Yumin,<br><br>Thank you very much for your suggestions. I will try based on your suggestions. Many thanks again.<br><br>Best regards,<br>Pengdong<br><br><div><div id="SkyDrivePlaceholder"></div>> Date: Thu, 10 Jan 2013 13:44:16 -0500<br>> Subject: Re: [vtkusers] 3D line and coordinate system<br>> From: yumin.yuan@kitware.com<br>> To: xiaopd@hotmail.com<br>> CC: vtkusers@vtk.org; vtk-developers@vtk.org<br>> <br>> Ok, from the email you sent to Sankhesh, I now understand what you try<br>> to do (and this seems to be similar to the other email thread I just<br>> replied)<br>> <br>> I think what you need is vtkPlane::ProjectPoint(...)<br>> // Project a point x onto plane defined by origin and normal. The<br>> // projected point is returned in xproj. NOTE : normal assumed to<br>> // have magnitude 1.<br>> static void ProjectPoint(double x[3], double origin[3], double normal[3],<br>> double xproj[3]);<br>> <br>> In your case, do the same for world_coordinate1, then to get the<br>> second point, you can try<br>> <br>> vtkPlane::ProjectPoint(world_coordinate1, camera->GetFocalPoint(),<br>> camera->GetViewPlaneNormal(), world_coordinate2);<br>> <br>> HTH,<br>> Yumin<br>> <br>> On Thu, Jan 10, 2013 at 9:04 AM, Yumin Yuan <yumin.yuan@kitware.com> wrote:<br>> > Which version of VTK is this?<br>> ><br>> > You can try to add the following after setting the two line points.<br>> ><br>> > line->Update();<br>> ><br>> > Yumin<br>> ><br>> > On Thu, Jan 10, 2013 at 3:47 AM, Pengdong Xiao <xiaopd@hotmail.com> wrote:<br>> >> Hi Yumin,<br>> >><br>> >> Thank you very much for your e-mail. After I change the following:<br>> >><br>> >> display1[2] = 0 ;<br>> >><br>> >> the problem still exists. After I click mouse, a line will be drawn, but it<br>> >> isn't perpendicular to the screen; and each time the length is different.<br>> >> Any other suggestions? Many thanks.<br>> >><br>> >> Best regards,<br>> >> Pengdong<br>> >><br>> >>> Date: Wed, 9 Jan 2013 10:31:29 -0500<br>> >>> Subject: Re: [vtkusers] 3D line and coordinate system<br>> >>> From: yumin.yuan@kitware.com<br>> >>> To: xiaopd@hotmail.com<br>> >>> CC: vtkusers@vtk.org; vtk-developers@vtk.org<br>> >><br>> >>><br>> >>> The VTK display coordinates' z range is 0 to 1, try this:<br>> >>><br>> >>> display1[2] = 0 ;<br>> >>><br>> >>> HTH,<br>> >>> Yumin<br>> >>><br>> >>> On Mon, Jan 7, 2013 at 9:16 PM, Pengdong Xiao <xiaopd@hotmail.com> wrote:<br>> >>> > display1[2] = -1 ;<br></div> </div></body>
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