Cad introduction pdf

As we move cursor over any tool in the tool bar a tooltip appears stating the name of that tool. And if we further wait for about three seconds, it turns into a brief description about that particular tool.

As shown by the following image. For more details we can press F1 key. Now I am going to draw a simple object. But first let us decide about unit system, we are going to use. Dimensioning in AutoCAD is automatic; lines, arrows and text are all taken care of by the dimension commands. AutoCAD dimensions are special blocks which can easily be edited or erased as necessary. AutoCAD provides lots of control over the way dimensions look. Using a system similar to text styles, dimension styles allow you to design dimensions so that they look just the way you want them to.

And from this menu select units. A pop up window will appear that will set our drawing units as shown below. Hatch patterns can be used to indicate a material to be used, such as a concrete hatch.

For example "School Chair". There will be three options for handling objects. The first is "Retain" - this is effectively using the "Group" command to group all objects into one "thingy" for manipulation.

Convert to Block gets rid of all the separate instances that make up the object, but makes it a block. It converts the object to a block, and then deletes it from the current drawing - but it's still loaded up and ready to be replicated throughout the drawing.

Insertion of Blocks To insert a saved block, go to the Insert menu, then Blocks, and select the name of the saved block you want to include; it'll appear at the point that you last clicked with the mouse. When the Block Definition window is opened, you can click the button by the words "Base Point" and define the default position in the drawing for inserted blocks to appear, which can be a real time saver.

You should also make sure that the units selected from the drop down menu match the units you're doing your drawing in; it's generally going to match by default, but it's the first place to look when you're tweaking something that's not working. This supplement focuses on tools and drawing aids that help you create 2D isometric views that look 3D, as if the object tilts toward you.

However, a 3D model provides a better way to display isometric views, for most applications. The term isometric means equal iso measure metric. An isometric drawing has no perspective, and therefore edges that are equal in length are drawn equal in length. The angles between the three principle planes and edges of an object are equal. All other lines are non isometric lines. Circular features appear elliptical in an isometric drawing. The views drawn with CADD have a number of advantages as compared to views drawn on a drawing board.

The views drawn with CADD are very accurate and provide a lot of flexibility in terms of editing and display. These activities would vary depend upon the application the object is to be subject to. Therefore the targeted of our discussion is to give you an overview of CAD and its applications would include the following:.

We translate a two-dimensional point by adding translation distances, tx and ty, to the original coordinate position x,y to move the point to a new position x',y'. The translation distance pair tx, ty is called translation vector or shift vector. Matrix representation of translation. Remember the change is size does no mean any change in shape. This kind of transformation can be carried out for polygons by multiplying each coordinate of the polygon by the scaling factor.

Sx and Sy which in turn produces new coordinate of x,y as x',y'. The equation would look like. NOTE: If the values of scaling factor are greater than 1 then the object is enlarged and if it is less that 1 it reduces the size of the object.

Keeping value as 1 does not changes the object. Uniform Scaling: To achieve uniform scaling the values of scaling factor must be kept equal. Differential Scaling: Unequal or Differential scaling is produce incases when values for scaling factor are not equal. The transformation can also be described as a rotation about rotation axis that is perpendicular to x-y plane and passes through the pivot point.

Positive values for the rotation angle define counter- clockwise rotations about the pivot point and the negative values rotate objects in the clockwise direction. In case of reflection the image formed is on the opposite side of the reflective medium with the same size.

Therefore we use the identity matrix with positive and negative signs according to the situation respectively. This transformation is referred as a reflection relative to coordinate origin and can be represented using the matrix below.

But many graphic application involve sequences of geometric transformations. Hence we need a general form of matrix to represent such transformations. This can be expressed as:. Where P and P' - represent the row vectors. T1 - is a 2 by 2 array containing multiplicative factors.

T2 - is a 2 element row matrix containing translation terms. We can combine multiplicative and translational terms for 2D geometric transformations into a single matrix representation by expanding the 2 by 2 matrix representations to 3 by 3 matrices. This allows us to express all transformation equations as matrix multiplications, providing that we also expand the matrix representations for coordinate positions. Thus, a general homogeneous coordinate representation can also be written as h.

For 2D geometric transformations, we can choose the homogeneous parameter h to any non-zero value. Thus, there is an infinite number of equivalent homogeneous representations for each coordinate point x,y. Each 2D position is then represented with homogeneous coordinates x,y,1. Other values for parameter h are needed, for eg, in matrix formulations of 3D viewing transformations.

Coordinates are represented with three element row vectors and transformation operations are written as 3 by 3 matrices. If two successive transformations T1 and T2 are applied to a coordinate position P, the final transformed location P' is calculated as:.

If the displacement is given by the vector the new object point P' x',y' can be found by applying the transformation Tv to P x,y. Translate the object so that the pivot-point position is moved to coordinate origin. Rotate the object about the coordinate origin. Translate the object so that the pivot point is returned to its original position. Translate object so that the fixed point coincides with the coordinate origin.

Scale the object with respect to the coordinate origin. Use the inverse translation of step 1 to return the object to its original position. Similar to 2D scaling an object tends to change its size and repositions the object relative to the coordinate origin. If the transformation parameter are unequal it leads to deformation of the object by changing its dimensions. The perform uniform scaling the scaling factors should be kept equal i. NOTE: A special case of scaling can be represented as reflection.

The most simple rotations could be around coordinate axis. As in 2D positive rotations produce counter-clockwise rotations. Rotation in term of general equation is expressed as. Three dimensional rotations require the prescription of an angle of rotation and an axis of rotation.

The canonical rotations are defined when one of the positive x,y,z coordinate axis is chosen as the axis of rotation. Translate origin to A1. Align vector with axis say, z 1. They accurately show the correct or true size and shape of single plane face of an object. The matrix for projection onto the z plane is. Notice that the third column the z column is all zeros. Consequently, the effect of the transformation is to set the z coordinate of a position vector to zero.

Axonometric projections overcome this limitation. An axonometric projection is constructed by manipulating the object using rotations and translations, such that at least three adjacent faces are shown. The result is then projected from the center of projection at infinity on to one of the coordinate plane unless a face is parallel to the plane of projection, an axonometric projection does not show its true shape.

However, the relative lengths of originally parallel lines remain constant, i. Trimetric 2. Dimetric 3. However only faces of the object parallel to the plane of projection are shown at there true size and shape, that is angles and lengths are preserved for these faces only.

In fact ,the oblique projection of these faces is equivalent to an orthographic front view. Cavalier 2. Cabinet Cavalier Projection-A cavalier projection is obtained when the angle between oblique projectors and the plane of projection is 45 degree. In a cavalier projection the foreshortening factors for all three principal direction are equal. The resulting figure appears too thick. A cabinet projection is used to correct this deficiency. Cabinet projection- An oblique projection for which the foreshortening factor for edges perpendicular to the plane of projection is one half is called a cabinet projection.

In contrast to the parallel transformation , in perspective transformations parallel lines converge, object size is reduced with increasing distance from the center of projection, and non uniform foreshortening of lines in the object as a function of orientation and the distance of the object from the center of projection occurs.

All of these effects laid the depth perception of the human visual system, but the shape of the object is not preserved. Perspective drawings are characterized by perspective foreshortening and vanishing points.

Perspective foreshortening is the illusion that object and lengths appear smaller as there distance from the center of projection increases. These points are called vanishing points. Principal vanishing points are formed by the apparent intersection of lines parallel to one of the three x,y or z axis. The number of principal vanishing points is determined by the number of principal axes interested by the view plane Perspective Anomalies 1.

Perspective foreshortening- The farther an object is from the center of projection ,the smaller it appears 2. This point is called the vanishing point. A vanishing point corresponds to every set of parallel lines. Vanishing points corresponding to the three principle directions are referred to as "Principle Vanishing Points PVPs ". We can thus have at most three PVPs. If one or more of these are at infinity that is parallel lines in that direction continue to appear parallel on the projection plane , we get 1 or 2 PVP perspective projection.

Engineering design requires ability to express complex curve shapes beyond conic and interactive Bounding curves for turbine blades, ship hulls etc. Lay down the initial control points 3. Use the algorithm to generate the curves 4. If the curve is satisfactory, stop 5. Adjust some control points 6. Objects can be classified into three types from a geometric point of views i.

The construction of 3D object requires the coordinate input of key points and then connecting them with the proper types of entities. Open navigation menu. Close suggestions Search Search. User Settings. Skip carousel.

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