Special Topic Raster2vector

8/4/2019 Special Topic Raster2vector

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Special Topic: Raster2Vector

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Raster-to-Vector scanning: Its application to CAD

Problem #1: you have old paper drawings that are

taking up valuable storage space. You're alsoconcerned about their fragility and susceptibility todamage. Also, you'd like to share copies of thedrawings with your co-workers, but feel that

making paper copies is too cumbersome.Solution: scan the drawings and archive theimages electronically. By making backup copies,you add permanency and security, not to mention

peace of mind. In addition, once in electronic form,the drawings can easily be shared with others byusing CD-ROM's, your company's intranet, or theInternet.




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Raster-to-Vector scanning: Its application to CAD

Problem #2: you're working on aremodeling project and have a set of blueprints showing existing conditions. Youneed a composite drawing showing what

stays, what's to be demolished and what'snew, but you don't want the expense of re-drawing the original blueprints.

Solution: scan the existing bluelines and usethem as background images in the new CADdrawings.




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Reasons of converting paper drawing to CAD

There are millions of drawings lying all around theworld.

These are invaluable pieces of paper, which havecreated monuments, buildings, machines andinfrastructures.

As the time passes by, these paper drawings areendangered being lost to disaster or being lost.

There is an urgent need to make sure that all thepaper drawings which are lying in offices, andsecured places to be restored in a manner whichwill enable them to be with us for a long time




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Ways of converting paper drawings to CAD

The various means by which to convert theold paper drawings to CAD are:

•Automatic conversion using software

•Manual conversion by draftsman

•Precision redrafting

•Scanning and storing




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Raster-

to-Vector scanning: The steps Raster-to-Vector scanning: The steps

Using TWAIN-

compliantscanners

despeckling,

deskewing,

Vectorizing•DXF file

Open the DXFfile in CAD•then save innative format




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Raster-to-Vector scanning: 1st step

Scan or load the image. TWAIN-compliant desktop

scanners such as Epson, HP,and etc,

Large format scanners, likeContex, Colortrac, Oce, etc.

Large drawings can bescanned on desktop scannersas a set of “tiles”, then re-assembled and vectorized inthe software.

The technology allowsscanning/saving A1 or A0drawings as BMP, TIFF, etc.

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Raster-to-Vector scanning: 2nd step

Clean the image.

Dirty images canbe automaticallydespeckled.

Skew drawings

can bestraightened.

Once the scanneddrawing is cleanand square it isready to beconverted into avector DXF file.

S i l T i R t 2V t




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Raster-to-Vector scanning: 3rd step

Vectorize.

Software is normallysupplied with defaultconversion settings.

Select the one that

best describes therequired drawing -Architectural, Map,CNC, etc.

Vectorize the scannedimage.

Settings can beadjusted to fine-tunethe results.

S i l T i R t 2V t




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Raster-to-Vector scanning: 4th step

Edit the vector file.• The software can

save black&white andcolor DXF files.

• Open the DXF file inCAD.

• Edit the opened fileas required and saveit in the native CADformat eg.,AutoCAD’s dwg files.



Special Topic: Raster2Vector 10

Issues in implementations

Layers as per client standards,

Dimensions with the respect to input,

Scale as per client requirement,

CADD standards like line type, line thickness, text

height, arrow type, Nomenclature, general notes,

dimension text & arrows etc,.

Title Block in relevance to drawing,

Annotations as per client standards,




How to scan a drawing for raster to vectorconversion

Not all drawings can be scanned to create araster image that can be used for raster to vectorconversion. For example:• Some drawings are so faint or so dirty that whatever

you do you will not be able to create a clean enoughscan for conversion.

• Some drawings or drawing details are too small to scanwell enough for vectorization, regardless of the scanningresolution you use.

• Some drawings contain so many overlapping details - for

example text written over drawing lines - that even if you get a perfect scan no raster to vector converter willbe able to unscramble the information




Color, grayscale or monochrome?

• Most scanners give you the option of scanning in color, grayscale ormonochrome.

• These options have different namesdepending on the make of scanner youhave.




Color

• Most scanners’ color option will normally create a rasterimage that contains 16.7 million colors.

• Only use this option if scanning a color drawing with aview to converting it to a color DXF file.

Do not use your scanner's color option if scanning a black

and white drawing.• Scanning a color drawing with a view to converting it to

a color DXF file entails experimenting the scanner'ssettings until the colors on the raster image are as highcontrast, vibrant and saturated as possible.

• Warning: Color images can be very large. An E/A0 sizedrawing scanned in color at 300 dpi will take up about385Mb of memory.




Grayscale

• Most scanners’ grayscale option (oftencalled black and white photo) willnormally create an image that contains

256 shades of gray.• Grayscale images are not normally

suitable for raster to vector conversion.




Monochrome

• A scanner's monochrome option (oftencalled line art, black and white drawingor 1 bit) will create a much smaller

image that contains two colors - blackand white.

This is the option one should normallychoose when scanning a drawing for raster

to vector conversion.




Thresholding

• When scanning a drawing in monochrome, the scanner orscanning software has to make a decision about which parts of the drawing to set to black in the raster image and which toset to white. This is called thresholding.

• If your drawing has faint lines or a dirty or tinted background

a user will have to experiment with the scanner's settings toget a raster image where, as far as possible, the parts of theraster image that are supposed to be black are black and theparts that are supposed to be white are white.

• If the scanner or scanning software sets too much of thedrawing to white, it may contain breaks and holes and faintparts may be lost. If your scanner or scanning software sets

too much of the drawing to black, text characters may "bleed"so that white spaces within them or between them becomefilled and speckles and dirt may appear in the background




Thresholding




Resolution

• It is not true that "the higher the scanner resolution, thebetter the vectorization results".

In fact, a high resolution scan can sometimes give worseresults than a low resolution scan!

• Be aware that decreasing the resolution of an imageafter scanning will prevent increasing it later.

Increasing resolution after scanning will not regain any lostdetail. It will simply exacerbate "steps" in the image thatwill decrease the quality of any raster to vector conversion.

• For most drawings, a scan resolution of 200 to 400 dpiis optimal.




Resolution

•Note that the separation of close together

entities is dependent on selecting an appropriatethreshold (see above) as well as on selecting anappropriate resolution




Edit raster images - raster effects and clean uptools




Edit raster images - color palette editing tools




Vectorization - vector recognition




BENEFITS OF CAD CONVERSION

• Perfect drawings, which can be modified as and when

required in the fastest possible manner.• Able to access drawings at a click of a button • Storage of the drawings becomes very easy • Can make multiple copies at no cost • Transmission of document is very fast

• Multiple print can be taken as a very high speed • Thousands of drawings can be stored in a single DVD / CD • A new file, we can create as many layers as you require. We

generate separate layers for dimensions, text, body, hiddenlines, and centerlines, etc.

• Text is separated and has its own layer and is recognizable

as text• Dimensions are intact and are shown by a separate layer.




Contd…BENEFITS OF CAD CONVERSION

• High accuracy

• Normally create a drawing as a new file; the finaloutput is editable and will be in DXF, DWG, DGNor any other CAD formats

• Cost effective hand-drawn conversions.

• The converted drawings are manually drawn withprecision and are fully editable and contains: Accurate layer information Accurate text (editable)

Accurate line types (editable)

Associative dimensions (adjustable)

Symbols & blocks of standard components Title blocks(as per scale)

Associative hatch patterns (editable)




Raster-to-Vector: Examples




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Raster-to-Vector: Examples_a




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Raster-to-Vector: Examples_b



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Raster-to-Vector: Examples_d




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Raster-to-Vector: Examples_e

Special Topic Raster2vector

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