Scale the vector image

 

When you scan a drawing and convert it to vectors it will not appear in your CAD program at the correct scale. This is because your scanner scans the drawing in units of measure called pixels, whereas your CAD program uses millimeters or inches etc.

 

To scale a vector image to the right size, use the Vector Scale Settings dialog. This appears when:

You select File Menu > Vector > Scale Options.
You have saved a DXF or HPGL file using File Menu > Vector > Save As and have clicked Yes to the Scale Prompt that appears after the save dialog.

 

There are three scaling options in the Vector Scale Settings dialog:

DPI
Geo

 

In addition, you can:

 

Scale using DPI

1. Click on the DPI option.
2. If the value in the DPI field is 0, enter the dpi resolution that you scanned the drawing at.

(If your raster image contains dpi information a value will be inserted here automatically.)

3. Enter the scale of the original paper drawing that you scanned in.

For example:

 

If the drawing was at 1:1 enter the scale like this:

 

If the drawing was at 1:50 enter the scale like this:

 

If the drawing was at 1″ = 1′ enter the scale like this:

 

If the drawing was at 1/8″ = 1′ enter the scale like this:

 

4. Select export units.

If you are going to save the vectors as DXF select the units your CAD program uses in the Export Units part of the dialog.

If you are going to save the vectors as HPGL, select HPGL plot units as the export units.

 

Because HPGL files use an integer coordinate system, scaling an HPGL file may give rise to inaccuracies in the positions of vector end points.

 

Scale using Distance

Suppose there is a line on your image that you know represents 8 miles – for example a scale bar on a map or a dimensioned line on a drawing. The Distance scaling option lets you use this information to scale the drawing.

 

1. Click on the Distance option.
2. Click on the Measure button.

The Vector Scale Settings dialog disappears.

 

a) On your image, position your cursor at the start of the known distance. Press down your left mouse button. Holding down your left mouse button, move your mouse to the end of the known distance. Raise your left mouse button.

The dialog reappears and the image length of the distance you have specified is automatically entered into the Image Pixels Distance box.

b) Enter the known distance into the Vector Units Distance field.

For example if the known distance is 8 miles, type 8.

c) Select the units the known distance is measured in.

For example if the known distance is 8 miles, select miles.

 

3. Select export units.

If you are going to save the vectors as DXF select the units your CAD program uses in the Export Units part of the dialog.

If you are going to save the vectors as HPGL, select HPGL plot units as the export units.

 

Because HPGL files use an integer coordinate system, scaling an HPGL file may give rise to inaccuracies in the positions of vector end points.

 

Scale using Geo

If your raster image is a GeoTIFF file, the Geo option will be selected automatically and values from the GeoTIFF file will be automatically entered into the Geo and Tie Point parts of the Vector Scale Settings dialog.

If your raster image is not a GeoTIFF file you can use the Geo option to scale the drawing as follows:

 

1. Click on the Geo option.
2. Calculate the distance that each pixel in the raster image represents in the X and Y directions.

Enter these figures into the Geo Pixel Scale X and Y boxes (the X and Y scaling factors will usually be the same).

For example, if 1 inch on a map you have scanned represents 100 inches on the ground in the X (horizontal) direction, and you scanned the map at a resolution of 300 dpi (dots per inch), then the distance represented by each pixel in the horizontal direction will be 100 / 300 = 0.3333333.

3. Assign coordinates to a known point (see below).

 

Assign coordinates to a known point

Suppose you are vectorizing a map and a known point on the raster image is at coordinate 10235,78653 on the map. In Scan2CAD you can assign the coordinate 10235,78653 to the point so that when you import the vector file Scan2CAD produces into your CAD program it will be placed in your CAD program at the correct coordinate location.

 

1. Scale the drawing using any of the methods described above.
2. Click on the Select button in the Tie Point part of the Vector Scale Settings dialog.

The dialog disappears.

3. Click on a point on the raster image that corresponds to a known coordinate.

The dialog reappears and the raster coordinate of the point you clicked on is automatically entered into the Raster Coordinate X and Y boxes.

4. Type the corresponding known coordinate into the Vector Coordinate X and Y boxes.

 

Enlarge or reduce the size of the drawing

1. Scale the drawing using any of the methods described above.
2. Enter values in the Scale Factor part of the Vector Scale Settings dialog.

For example, entering 2 into the Scale X box and 2 into the Scale Y box will enlarge the drawing by a factor of 2 in both the X and Y directions.

 

Have questions on this topic? Talk to us