Do You Need Raster to Vector Conversion?

Eight Questions to Ask

Those of us who are in the business of CAD conversion regularly use terms like raster to vector conversion, or the shortened form, R2V.  But it was brought to my attention last week, that if you’re not in the CAD conversion business, you might not even know what raster to vector conversion is, or why you might need it.  So, we’ve compiled a list of eight questions that you can ask to determine if you need raster to vector conversion. Raster to vector conversion

But, before we get to the right questions, let’s define just what raster to vector conversion is:

Raster to vector conversion is the process of converting a raster image to a vector image.  R2V can sometimes be done using an automatic R2V converter software; sometimes it needs to be done entirely by hand, as in tracing and re-drawing a raster image to recreate it in the vector; and sometimes, probably most often, it is a mix of automatic an hand conversion.

1.  What is a raster image?

A raster image is an image that is made up of pixels which are little squares or dots, like the images you see on your computer monitor or TV screen.  Raster images are created when you scan a drawing, take a photograph with a digital camera or create an image in a raster-based software program such as Adobe Photoshop.

Raster images can be saved as various sorts of file including BMP, CALS, GIF, IMG, JPEG, PCX, PDF, PNG, and TIFF.

2.  What is a vector image?

A vector image is an image made up of vectors (lines) which are mathematically defined entities drawn between coordinates.  Vector images are created by CAD programs and other vector-based software programs such as Adobe Illustrator.

Vector image file types include DXF, DWG, DGN, HPGL, SVG, EMF, WMF, and PDF (which can contain raster images, vector images or both).

3.  Why convert raster images to vector images?

Some software applications require vector images in order to work accurately with the images. The following questions provide some examples.

4.  Do you have scanned AEC drawings that you need to import into your CAD system?

If you’ve scanned old AEC drawings in order to bring the digital files into a CAD program, you need R2V conversion.  While you will probably be able to load a raster image into your CAD program and view it, you will not be able to make any changes to it without converting it to vector.

5.  Do you want to cut a scanned image using a CNC machine? 

Just like CAD programs, CNC programs will work only with vector files.  This means that you must either redraw the scanned (raster) image manually or get a raster to vector conversion service to convert it for you.

6.  Do you have files such as JPEGs, BMP, TIFF, IMG, GEM, CIT, GIF, but you need EPS, PDF (which can contain raster and vector) DXF, DWG, DGN, HPGL, SVG, EMF, WMF?

The first group of file types is raster files.  The second group is vector files.  You can’t just open a raster file and click “save as” to turn it into a vector file.  The only way to get a vector version of a raster file is by going through the process, whether automatic or by hand, of raster to vector conversion.

7.  Do you have satellite imagery that needs to be brought into a GIS (Geographic Information System)?

Satellite imagery, by its very nature, is a raster file.  It is, after all, just very large photograph.

When I thinking about satellite imagery, it’s important to remember that almost every pixel in a detailed satellite image of an urban area could contain unique information.  For instance, a single tile in a web map typically has 256 x 256 = 65,536 pixels, and each zoom level has (2^zoom * 2^zoom) tiles.

A vector map, on the other hand, is made up of polygons and lines. For example, a shapefile detailing zoning boundaries of an entire city (potentially millions of Raster tiles) area might only have 65,000 Vector shapes.

The most obvious difference between raster fixed pixel maps and vector (coordinate maps) is that vector maps can scale with a higher degree of accuracy than pixels because vector data contains coordinate patterns (points, polygons, lines etc) that can be rendered relative to each other at different resolutions using simple formulas, while pixel resizing typically uses an algorithm to smooth out the pixels, and that results in image artifacts.

While both raster and vector data have their places in GIS, you will definitely need to go back and forth between the two.

8.  Do you have satellite imagery that needs to be brought into CAD?

Yes, it’s true, not all mapping applications are done in GIS…some are done in CAD.   For instance, AutoCAD Map adds GIS features to the base AutoCAD product and, as such, these features help define the difference between CAD and GIS.

The primary difference between CAD and GIS is topology. GIS has it, CAD doesn’t. In a CAD environment, the objects (lines, polylines, points, etc.) have no relationships between them. Topology brings these objects together into logical groups to form real-world relationships.

CAD models represent things in the real world, but GIS models represent the world itself.  GIS adds attributes to each object, and those attributes position the object in the real world.  The attributes typically reside in a database that is associated with the image.

If you answered “yes” to any one of these five questions, then you need raster to vector conversion.


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