Perspective in the graphic arts, such as drawing, is an approximate representation, on a flat surface (such as paper), of an image as it is perceived by the eye. The two most characteristic features of perspective are that objects are drawn:
- Smaller as their distance from the observer increases
- Foreshortened: the size of an object's dimensions along the line of sight are relatively shorter than dimensions across the line of sight .
Source:http://en.wikipedia.org/wiki/Perspective_%28graphical%29
Sketching is a rapidly executed freehand drawing that is not intended as a finished work. If in oil paint it is called an oil sketch. In general, a sketch is a quick way to record an idea for later use. Artist's sketches primarily serve as a way to try out different ideas and establish a composition before undertaking a more finished work, especially when the finished work is expensive and time consuming.
Source:http://en.wikipedia.org/wiki/Sketch_%28drawing%29
Technical drawing, also known as drafting, is the academic discipline of creating standardized technical drawings by architects, interior designers, drafters, design engineers, and related professionals. Standards and conventions for layout, line thickness, text size, symbols, view projections, descriptive geometry, dimensioning, and notation are used to create drawings that are ideally interpreted in only one way.
