Scaling Images in Autodesk Inventor

9 Nov, 2010 By: Rusty Belcher

Avatech Tricks Tutorial: You can use a 2D image as the basis of your next 3D model, but only if you know how to adjust the image to full scale.

Editor's note: This tutorial courtesy of Avatech Solutions.

Many 3D projects start off with a single picture or digital image. These images are often inserted into the CAD program and used as the initial 2D design for the eventual 3D model. Designers commonly encounter problems, however, when trying to build a 3D model from a 2D image. It is very difficult — or impossible — to adjust the size of the image to full scale.

In this tutorial, I will demonstrate the process of adjusting the size of a digital image to full scale in Autodesk Inventor. Before we start this process, it's important to note that you can never truly make a picture or digital image full scale. You can get close, but 100 percent accuracy is not possible. The accuracy of this process is based on the quality and resolution of the image being used; higher quality and higher image resolution will increase the level of accuracy.
Inserting an Image into an Inventor Sketch

The process starts in an Inventor Sketch. I have my Inventor application open and I am working on the first sketch of my part. I will use the Image command to select and insert the desired digital image. You can link the image to the part file, but in this case I will clear this default option and embed the image.

We will center the image at the origin and make sure the image remains horizontal by applying geometric constraints to the image edges.


Creating a Scale Parameter

We need to create a parameter that will allow us to modify the scale of the digital image. In the parameter dialog, I will create a user's parameter called "Scale." We will set the unit of this parameter to Unitless and the initial equation value to 1. This parameter will be used each time we place a dimension on the image.

Adding Dimensions to the Image

We can adjust the size of an image in Inventor by applying dimensions to the edges of the image. We can also add geometry to represent the size of a scalable object in the image. In this example, the rear tire of the bike is known to be 20" in diameter. We will add a string of lines from the corner of the image to the base of the tire. Then we will add a line that represents the tire diameter. We cannot snap to the image, so we will zoom in and try to make the best manual placement possible, remembering that these picks will affect the overall accuracy the model.

Now we need to add the dimensions to the geometry. We will start by dimensioning one edge of the image. We will leave the initial value alone, but we will modify the overall value, adding an equation that multiplies the initial value by the scale parameter. Because the current value of the scale parameter is set to 1, there will be no change to the size of the image.

This process is repeated for each line we created to define the scalable object in the image. In each case the initial value of the dimension is multiplied by the scale parameter.

Now for the Math

At this point we focus on the dimension that defines the scalable object. We know the current size displayed by the dimension, and we know the desired size. We can calculate the scale factor by dividing the desired size by the displayed size.


Changing the Scale Parameter

Once we know the necessary scale factor, we can replace the current scale parameter value with the new value.

As we exit the parameter dialog, the image and all supporting geometry is adjusted to suit the new scale value. Now our image is as close to full scale as possible.

Let the Modeling Begin

Now that we have a full-scale image, we can save the component and use it as the base part in a new assembly. We can create new components using the image part as the sketch plane. We can also trace the image to create the necessary sketch geometry for the 3D model. As we sketch, it is important to use real-world dimensions and not rely on the graphics too much. The graphic is used as a guide, but the real-world dimensions will be used to ensure the accuracy of the final design.


About the Author: Rusty Belcher

Rusty Belcher

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