Edit Surface Data Help

This widget allows a user to specify a point or region of a surface. The region is outlined. Once specified, the point or region can be translated (moved) in several different ways. Thus surfaces which are not accurate can be modified. The changed surface can be viewed immediately and/or saved (via the Write Surface menu option in the File menu on the DAVE master widget - but I'm not certain this option works). The Edit Surface Data widget has not been used very much so it may be a bit cumbersome and buggy. If you think what it does is (or could be) useful, let us know so we can make it better.

Each object (as read in, for example, from a points file produced by Planimeter) has a (U,V) coordinate system describing all the points on its surface. The U coordinate typically goes around the object and the V coordinate goes along its length. This is similar to the latitiude and longitude coordinate system for describing a point on the Earth.

Choosing a Point on an Object

To pick a point on an object, first choose which object you are interested in. The box under the heading "OBJECT" will toggle through all known objects as you click on it with the left mouse button. Alternatively, if you hold down the right button you will get a menu of objects from which to choose.

A (U,V) coordinate can be specified by clicking the left mouse button while the cursor is in the coordinate pad (the "Select Point" region with the cross- hair in it). The chosen coordinate is shown in the U and V boxes below the coordinate pad. Each coordinate can also be changed by clicking on the arrow keys to either side of the U or V boxes.

The chosen surface point is visually identified by a green line which is displayed in the viewing window. The line is perpendicular to the surface at the specified point.

Moving a Chosen Point

A point is moved by sliding the green slider to the right of the coordinate pad. Moving the slider up moves to point outwards, moving the slider down moves the point inwards. The point moves in the direction of the green line, which by default is perpendicular to the surface. The orientation of the green line can be changed by modifying the X,Y, and Z coordinate values of its tip (relative to its base I think). You may want to rotate the object a bit to better see the changes in the orientation of this line.

If you like the way the surface looks after you move the slider, then click on ACCEPT, this will accept the change and reset the slider. If you don't want the change, click on CANCEL (then,to reset the slider, click on ACCEPT). I don't know what SEND does.

Choosing a Region on an Object

To choose a region of an object, first set "Region Type" to Box. Then, a region is specified by holding down the right mouse button while the cursor is in the coordinate pad region. With the button down, move the mouse. A box should appear going between the initial coordinate where the button was pressed and the present position of the mouse. Release the button when the box surrounds the correct region of the object (the region is outlined in green in the main viewing window). Note: you may have to be a bit patient moving the cursor when the right button is down, the box may lag a bit (this is because the outline on the object's surface in the viewing window is being simulaneously calculated and displayed).

The chosen region (and the chosen point) can be changed just as a chosen point is changed (by clicking on the arrows beside the U and V boxes). In this case both the chosen point and the chosen region is translated as specified.

Moving a Chosen Region

A region is moved the same way as a point, i.e., by moving the green slider and either ACCEPTing or CANCELing the change. By default all points in the region are moved by the same amount. However, if "Interp. Type" is set to "Linear" then there is a linear falloff in the amount any point moves, relative to the point chosen by the crosshair in the coordinate pad. Thus, points closer to the chosen point move the most, and points closer to the boundary of the chosen region move the least. This creates a smoother blend between the moved region and the rest of the object. Similarly, if an interpolation type of "Quad." is chosen, a quadratic falloff in the amount of movement is applied (thus the falloff is faster).
Copyright 1995 by Lawrence M. Lifshitz and the University of Massachusetts Medical School. All rights reserved.