# Working with Pictures and Drawings

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Transformed images of pictures and drawings provide compelling and revealing ways to view and understand geometric and mathematical transformations. Sketchpad provides a number of ways of transforming pictures and creating objects based on pictures.

| Create a Locus of a Picture or Drawing

To create the locus of a picture, the shape or position of the picture must depend on a point that can move along a path or on a parameter that can vary. Select the picture and the point or parameter and choose Construct | Locus. The locus of the picture appears. | Driver: Parameter Elevation Domain: 0° ≤ Elevation ≤ 180° Driven object: Picture Attached to P'

| Create an Iterated Image of a Picture or Drawing

To create an iterated image of a picture, the shape or position of the picture must depend on a pre-image point or parameter. Select the pre-image object(s) and choose Transform | Iterate. The picture is iterated along with the points it depends on. |

| Crop a Picture or Drawing to a Polygon

To display only the portion of a picture that overlaps a polygon, select the picture and polygon and choose Edit | Crop Picture to Polygon. The original picture is hidden, and the new cropped image appears in a layer on top of the polygon. |

| Define a Function Based on a Drawing or Picture

To define a function based on the top edge of a picture or drawing, select it and choose Number | Define Function from Drawing. The value of the function is determined by the highest opaque pixel at each location in the function’s domain. Use the Marker tool to draw the desired graph of your function, and then define a function based on your drawing. You can use it in the same way as other functions: evaluate it, transform it, and so forth. You can even modify the function by creating a new drawing, copying it, and choosing Edit | Paste Replacement Picture. |

| Change the Color of a Drawing

After you create a drawing using the Marker tool, you can change its color using Display | Color.