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If these FAQs don't answer your paper
to CAD conversion Send an email with your |
Basic Questions on Paper to CAD (raster to vector) and CAD to paper
(vector to raster) processes
...scanners, scanning, raster images, pixels,
resolution, what's a raster vs. a vector, CAD vector file formats,
engineering document management, conversion bureaus, etc. |
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| Questions specific to TracTrixTM software | |||
| Definitions | |||
| We've tried to be objective and hope the answers are useful to anyone wishing to learn about paper to CAD conversion. We welcome comments. | |||
| What's the difference between raster and vector files? | A raster image is roughly
equivalent to a newspaper photograph. If you look closely you see that
it is made up of lots of small dots. The density of these dots is
referred to by resolution, measured in dots per inch (stated as 'dpi').
Raster files are stored in many file formats, TIFF is a common example. Vectors are used to describe specific objects defining their size, position and geometry. The image seen on screen in a CAD application is only a visual representation of the vector file. The vector information in a CAD file is mathematical. It is not stored as an image. So, for example, a vector line is an absolute line connecting two or more points; a vector curve is described by source coordinates, a polynomial equation and end point coordinates. Vector information is stored in many different file formats, one of which is DXF. The primary function of the DXF file is to permit CAD vector information to be exchanged between different CAD applications. |
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| Do scans work in a CAD program? | Scanners produce raster
images, not the vectors used in CAD programs. When CAD software allows
import of a raster, it will display it as a raster (i.e. dot based)
image within the CAD document. The lines in a raster image in a CAD document cannot be manipulated. The CAD program will not convert it to vectors. |
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| What's the difference between pixels and dots per inch? Is a dot a pixel? | A pixel is a minute circular point of light about 10 or 12 thousandths of an inch in diameter (sometimes stated as 10 or 12 'mils') created on a monitor screen. A dot is a sample taken by a scanner for representation in a raster image. A 300 dots per inch (dpi) scan takes snapshots of dots which are about 3 mils across (3,33333....mils to be exact). To represent a 300 dpi scan on screen at a 1:1 scale your computer typically has to consolidate groups of 16 dots (each 3 mils diameter) into a single pixel (10 - 12 mils diameter). This means that the raster image you see on screen is only an approximation of the underlying digital 'dpi' information from your scan. And your scan itself is an approximation. Sometimes the screen appearance can be disconcerting. |
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| In image resolution, what's the difference between, say, 400 dpi true and 400 dpi interpolated? | True resolution is the
number of dots per inch of reflected light captured by the scanner head.
The scanner head is physically limited in the number of dots which it
can capture. Interpolation software (usually built in to the scanner, but also available in raster manipulation programs) can make a good guess at what lies between the dots recorded by the scanner. By comparing adjacent dots captured in a true 200 dpi scan interpolation software might replace each dot with four new ones (creating a 400 dpi interpolation) or even nine new ones (creating a 600 dpi interpolation). For many applications (including the majority of paper to CAD conversions) interpolation works well. But interpolation will never be as accurate as a true resolution. |
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| How can I use my desktop scanner to create CAD files? | Paper to CAD (raster to
vector) software such as TracTrix take your scans, convert them to
vectors and output them as a DWG,DXF, IGES or other vector file format. This vector file can be imported directly into your CAD software. All of the popular and widely used CAD software applications accept DXF files. |
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| Why can't I just edit my raster files and not have to bother taking them to vector? | Raster files are excellent
for visual purposes - after all they are a picture of the original
image. Adobe
Photoshop, Corel and other excellent raster editing softwares are
available to enable you to edit raster images. However all CAD software (and some graphics drawing packages) use vector objects instead of rasters. The primary benefits are ability to precisely describe, create, scale and manipulate individual objects. There's also efficiency in storage and output to plotters or printers. |
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| Is there an international standard for vectorization? | No. But conversion of paper
to CAD may provide you and your organization with an excellent
opportunity to begin implementing ISO 9000
quality standards. A good engineering document management system goes a long way towards meeting the ISO standard. |
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| I've too many drawings to vectorize in-house. How should I choose a bureau? | There is a pretty clear
relationship between price and quality in bureau conversion. We
recommend starting with a pilot project comprising two stages. In the
first stage establish that the bureau can deliver to your required
quality for a small sample of drawings, say five or ten.
From this limited experiment set the parameters for a second stage test with a much larger sample of your drawings (maybe 5% of your stock). The second stage determines how your bureau will perform under a real load. You and your bureau can establish a solid relationship during this test and sort out potential problems. And most important, involve your eventual users in the test. Have them check that the quality meets their needs. Some users may need help in defining their needs. |
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| If I have a small or hand-held scanner, can I scan a big drawing in pieces and 'stitch' them together afterwards? | Yes. But we don't recommend
it if there is a significant quantity of large drawings to vectorize.
The drawback is the number of scans you have to make to capture, say, a
'D' size drawing which would require eight 8 1/2" X 11" scans in a
desktop scanner or three scans with an 8" wide, hand-held rolling
scanner. Add to that the "stitching" time in your CAD package. Users do this only when they have minimal quantities of drawings larger than 'A 'size. There is no limit to the size of image which TracTrix for CAD can vectorize. If you have access to a large format scanner use it instead of stitching. Most urban areas have copy shops or similar reproduction shops where a large document can be scanned to disk at very reasonable prices. For instance a busy 'E' size drawing scanned at 300 dpi monochrome (black and white) can be stored on a 3 1/2" diskette. The raster file on disk can be vectorized in TracTrix for CAD later. |
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| What should I be aware of before I start converting images to CAD? | Vectorizing packages do not
add information to your original drawing. We tend to think of drawings
as being super accurate. This is not true. An image on paper is
imperfect, inaccurate and imprecise. This may seem like a heresy to
all who (like us) have slaved over drawing boards. Think about what we
do when we 'read' a drawing:
Our intellect works wonders piecing together the disparate pieces of information which our eyes pick up from a drawing. Our brain automatically sorts text from linework and combines different sorts of visible information into a comprehensive whole. With this we can mill our piece, set our forms, etc. to the designer's requirement. Contrast this with CAD. When we work in a CAD package vector information is created. The dimensions are the primary information and the CAD package produces a visible representation on screen (or to a plotter) based on these dimensions. This output is an approximation from the absolute dimensions of CAD. We go through the same processes to beginning milling or setting up our formwork. And whether the information began in CAD or on a drawing board, we adjust it to the accuracy needs and limitations of the real physical world. So what's the process involved in translating paper to CAD? It always requires two stages. In the first you scan and convert raster image of the original drawing to CAD vectors . In the second, you must check that the CAD representation created by vectorizing meets your need for accuracy and purpose. You've probably heard the expression "garbage in, garbage out". This is not more true than scanning a paper drawing and vectorizing it. Vectorizing software can only make vectors where there is raster information for it to track. Breaks in the lines, poorly connected lines at corners, blobs in the image at multiple line intersections and similar imperfections in the raster image all contribute to imperfect vectors. TracTrix is used by a major prosthetics manufacturer to create cutting and drilling templates for microsurgery. Their originals are very finely detailed. Generally, the accuracy you'll achieve will depend primarily on the quality of the original drawing. Accuracy can then be made absolute in whatever CAD software you are using. You should always expect to take raster images automatically to vectors and then edit them to the precision your application requires. |
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| What is the difference between accuracy and precision in vectorizing? | Repeating the point in the
previous section: Scanning paper to create a raster image does not
improve the quality in any way. TracTrix (and all other vectorizing
software) can only vectorize that which it can 'see', the raster image.
The resultant vectors are no more perfect than the raster.
Vectorizing is accurate to the extent that
the vectors are an accurate representation of the raster image. Is this
'accuracy' good enough for your application? Perhaps. But if it isn't,
the vectors can be edited to make the vector file as precise as you
require. Remember, vectors can be made to be mathematically perfect,
rasters cannot. |
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| Does high resolution (dpi) assure vector accuracy | TracTrix follows either the
centerline on lines or the outline of images. It achieves this by
looking for pixels. In centerline tracking, TracTrix looks for the
chosen line width by looking at pixel quantities across line and seeks
the mean center of the line. Having more pixels from a higher resolution
will not necessarily create a "better" mean centerline. When following an outline it looks for pixels on the edge of the image. Higher resolution might present a 'smoother' less jagged edge for TracTrix to vectorize but the vectors are not more accurately created. When following an outline it looks for pixels on the edge of the image. Higher resolution might present a 'smoother' less jagged edge for TracTrix to vectorize but the vectors are not more accurately created. Higher resolution makes for bigger files to manipulate. Bigger files require more pre-processing storage and processing takes much longer (twice the resolution means four times as many pixels to store and process). As a general rule, there are rapidly diminishing returns from increasing resolution for raster to vector conversion. We tend to use 300 dpi or 400 dpi. Occasionally we need 600 dpi. |
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| The horizontal and vertical vector lines on screen do not appear to be straight, but they were in the original drawing. Why? | What you see on screen is
only a visual display of the actual stored CAD file and does not
represent what the file will create on a plotter or printer. The vector
points, also seen on screen, more accurately depict the vectors as they
will be plotted. What you are seeing is the result of a slightly askew
scan. When a computer depicts straight lines on screen they will appear straight, without a jagged appearance, only when they are absolutely square to the screen's matrix. If they are slightly off square the computer tells the screen to depict the straight line as a Cathode RayTube scan series which might be: Fill 100 pixels horizontally, go down 1 pixel, fill 100 pixels horizontally, etc. It is this small one or two pixel step down which makes straight lines appear to have a jog or appear jagged on screen. The underlying vector which it is representing is a single point-to-point line. Consider the jogs to be an optical aberration and not representative of the actual vector. In TracTrix, one can see the actual vector points at each end of the line by clicking on the line. |
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| How come some vector files are bigger than the raster image file? Should this happen? | The raster image size is
based upon the resolution (dpi) and the physical size of the image. The
vector file size is based upon the number of vectors required to
represent the raster file: 1) Say the raster image is comprised of curved lines and the vectorizing software mode selected only creates vector files comprised of straight lines, arcs and circles. In this mode the resultant vectors of the curves have to be represented by an arc, or a line or a circle. A curved line cannot be well represented or fitted by a line or a circle. That leaves the arc. The curves have to be fitted by arcs which generally means the raster curves become a very large collection of small arcs (vector points). So, the simple raster curve becomes a complex and very large collection of arcs. TracTrix can recognize straight lines, arcs, circles and complex curves called Beziers and splines. This means that instead of representing a curve with a large quantity of small arcs, we can show the curve by a higher order mathematical representation called a Bezier curve. A Bezier will capture a complex curve with far fewer vector points than the same curve captured with simple arcs. If you look at the TracTrix logo it shows four vector points which are a Bezier representation of the reasonably complex TracTrix curve. 2) In those instances where dashed or dotted lines are in the raster image, a vectorizing software may create vectors at the beginning and end of each dash or dot thus creating a multi-point vector file instead of a single pair of vectors describing the dashed or dotted line. 3) If the 'Outline' mode is chosen in a vectorizing software, then a single line, which ordinarily would be vectorized on the centerline, is vectorized on both sides and around the ends thus creating what amounts to a double line and a little more than double the file size. |
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| My drawings are already in CAD. How do I publish them electronically around my company? | There are many powerful
workflow and EDM (Engineering Document Management) applications
available. Also, take a look at Adobe Acrobat®format (those files with the .pdf suffix). Our colleagues in our Swedish conversion bureau have successfully used Acrobat as a basis for a substantial convert and catalog project in an engineering/marketing environment (we'd been successfully using Acrobat files for small scale projects - brochures, catalogs - We were pleasantly surprised that it scaled up so well). |
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| How can I publish engineering drawings on the Internet? | If you are interested in
publishing technical information on the World Wide Web,
Adobe publishes Acrobat 3. This
permits individual pages from an Acrobat document to be served instead
of the whole document - the present implementation. Great potential if
we can keep our screen 'pages' to reasonable sizes for serving (yes, we
know this page is growing a little too large - physician heal thyself) . DWF®- drawing web format, new from Autodesk, also shows promise in this area. |
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| Questions specific to TracTrix Software | ||
| What is the typical TracTrix Paper to CAD conversion process? | Scan your original into
TracTrix. Select the description which fits your type of drawing from
pre-defined types (e.g. architectural, contour, illustration, logo,
mechanical). Select the portion of the drawing to convert. TracTrix then automatically processes the raster lines into vectors. Compare the vectors with the underlying original raster image and make any post-processing changes using TracTrix' built-in vector editing tools. Export the result in the vector format of your choice. |
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| Speed/Expectations | TracTrix typically can
convert a busy E-sized drawing in about fifteen minutes on a 486/50
machine (faster on Windows '95). In our years of providing image conversion for customers we have learned that individual needs are unique. So we are reluctant to suggest exactly what savings TracTrix can bring you. But based on the tens of thousands of drawings that we've converted in our own bureau, we'd hazard a guess that after building in post-processing clean-up you could aim for 50% savings in hours spent on conversion. That's not to say that all drawings lend themselves to raster-to-vector conversion. Depending on quality and intended application, you'll find some drawings can be almost entirely vectorized using TracTrix, others may inevitably require manual redrawing. |
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| Will TracTrix give me a DWG file? | Yes. TracTrix for CAD
Release 2 will. TracTrix software also generates DXF and other vector description files which import into virtually all CAD packages. After you have imported the DXF file into your CAD package you have a CAD document on your screen. Only when you open and save this from within CAD does it create the native CAD file for your CAD package. |
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| Do I have to use TracTrix to drive my scanner, or will any image file work? | TracTrix can start with a
raster image file from many different sources. Your, or your vendor's or
your bureau's scanner(s) will produce a raster image file which TracTrix
can work with. See below Depending on version of TracTrix used, TracTrix can import ATT, BMP, BRK, CALS-Group 4 Type 1, CALS-Group 4 Type 2, CLP, CUT, DCX, DIB, GEM IMG, GIF, GX2, GTX G3, GTX G4, ICA, ICO, IFF, JPEG, JEDMICS, KFX, LV, PCX, MAC, MSP, PCD-Photo CD, PICT, PCX, PSD-Photoshop, RAS, RLE, RLC, TGA, TIFF- Pack Bits, TIFF-Modified Huffman, TIFF-LZW, TIFF-Group III, TIFF-Group IV, TIFF-JPEG, WMF, WPG, XPM, XBM, XWD. Depending on version of TracTrix used, TracTrix can export DXF (R12 and R13), DRW, EPS (AI-88), HPGL, HPGL/2, IGES (4.0 and 5.1), WMF and TIX formats. |
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| Is TracTrix a scanner? | TracTrix is software. It
does not include hardware. TracTrix can either drive or use the raster
output from practically every scanner available. If you do not have a
scanner you will need to acquire one to run TracTrix (unless you
plan to use a bureau for your scanning). Plan
to purchase a scanner which generates at least 300 dots per inch
resolution and, preferably, supports the TWAIN interface. You should also look for a scanner which also scans and outputs in color so that you can take advantage of the vectorization from colored originals and other enhancements of TracTrix for CAD Release 2. |
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| I have an old scanner. Will it work with TracTrix? | If your scanner can create a monochrome (also called bi-tonal or black and white - i.e. no shades of gray) TIFF, CALS or one of many other monochrome image file formats you can use TracTrix. | |
| Is there any way I can use TracTrix without a scanner? | You could go to a scanning
bureau to have your scans done. Or you could try using your fax modem,
although we don't recommend this approach. Bureaus: You could have your drawings scanned at a bureau, put the images on disk, tape or CD ROM and use these stored raster images as input to TracTrix. A disadvantage of this approach is that you will not be able to experiment easily with scanning difficult images - dirty, delapidated or cluttered ones - so that they vectorize optimally. You and your bureau should establish clear quality control procedures for the scans, preferably after running a pilot study using a good sample of your drawings. Alternatively, for large conversion projects, you may want to consider contracting out all the work to a bureau. Legacy Scans: If you already have stored binary images from previous scans, they can probably be taken into TracTrix with no problem. Some experimenting may have to be done to achieve this. For additional help with poor quality images ask us for a copy of our note 'Cleaning up dirty drawings for ease of viewing or vectorization'. Using a Fax image: We know of
users who fax drawings to their computer's fax modem (using the fine
setting) and open the stored fax image in TracTrix to create vectors.
However we don't recommend this approach. TracTrix works best with
images of at least 300 dots per inch or 400 dots per inch. Normal fax
standards do not support this level of resolution. |
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| What will I save by using TracTrix? | Exact savings depend upon
the quality of the original drawing and the type of image being brought
into CAD. Some users report costs savings as high as 80% against
conventional methods such as complete redraws, tablet digitizing and
heads-up digitizing. And for some images, such as contours, automatic
vectorization by TracTrix saves even more. Taken over a library of original drawings we think you might realistically expect that the total time required to scan, vectorize with TracTrix and perform post-conversion tidy-up would be around 50% of what it would take for manual redrawing in CAD. However, every user's originals are different. |
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| What does TracTrix do with text, symbols, Optical Character Recognition (OCR) ? | TracTrix does not purport
to be a text recognizing nor OCR software. From our experience, text on
engineering drawings, especially numerals and angled text, cannot be
captured well with present OCR technology (and we've been shopping for a
good OCR technology for five years now - see below). Hand drawn letters and numerals often look alike and are very difficult for the eye to discern. For example, we find that the hand drawn 'B' and '8' are quite frequently mistranslated, the capital letter 'G' is often mistranslated as a '6' and vice versa. Text at any significant angle to the normal axes is missed entirely. Post OCR editing time to find and correct the things that were missed or worse, erroneously translated, takes longer than keying in all the text. The comments for text apply equally to symbols. TracTrix vectorizes text unless the text portion of the drawing is excluded from vectorizing in advance. To replace the vectorized text the user simply draws a window around the vectorized text and keys in the required text in their CAD package. Trix Systems is continuously reviewing OCR and pattern recognition technology. When it is adequate for engineering users we will incorporate the technology. Recognition of shapes is also not yet available - this 'pattern recognition' problem is similar to that with OCR - the mathematical techniques available for our present processors are just not accurate enough (if you happen to be working on the math of pattern recognition, please let us know). |
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| Can I just vectorize what I want and not the whole drawing? | Yes. TracTrix allows "windowing" around that portion you wish to vectorize. | |
| Does TracTrix despeckle or eliminate "noise"? | Despeckling or noise elimination means eliminating small groups of pixels which create visual 'dirt' or visual clutter in a raster image. TracTrix settings allow the user to define the minimum size of object to be vectorized. In this way 'dirt' is ignored and not vectorized. | |
| Does TracTrix do orthogonal adjustment? | Squaring up corners is referred to as orthogonal adjustment. TracTrix for CAD provides this facility. | |
| What does TracTrix do with dashed lines? Is each dash a separate vector? | Presently, yes. A forthcoming release will have the facility of recognizing dashed and dotted lines as special objects and uniquely vectorize them. | |
| Does TracTrix recognize circles? | TracTrix for CAD recognizes circles as well as arcs, lines, polylines and Bezier curves. | |
| How far can TracTrix zoom in? | It can zoom enough so that the user can see down to the single pixel level. | |
| Can TracTrix show a vector over a raster? | Yes, this is a facility in TracTrix for CAD and is a handy way to check that the vectors represent the raster image. | |
| Can TracTrix show dimensions in metrics and/or inches? | Yes, it's users choice each time it's used. | |
| Can TracTrix be set to jump a gap in a line? | Incomplete or broken lines can be edited into complete or single lines within TracTrix vectors or in your CAD software. | |
| How many layers can TracTrix put vectors on? How does it do it? | TracTrix for CAD can create
and place vectors on a near unlimited number of layers. This is achieved
by identifying in advance the different raster line widths to be
vectorized then each set of line widths is placed on different layers
after vectorization. TracTrix for CAD Release 2 recognizes offset colors. It will vectorize each different color and place the resultant vectors from each color on different layers. This too will provide an unlimited number of vector layers. |
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| Can I use TracTrix without a CAD package? | TracTrix does not require a CAD package to vectorize nor to edit the resultant vectors. Most users do have a CAD package into which the resultant TracTrix vectors are taken either before or after editing in TracTrix. | |
| Does TracTrix support cut and paste or Active X? | TracTrix for CAD is written to the latest 32-bit Windows standards (including Windows 95 and NT 4). Release 2 implements both cut-and-paste and Active X (OLE2). | |
| How does TracTrix raster to vector conversion work? | An algorithm in TracTrix is
designed to seek the pixels in the raster image and 'follow' them
according to the parameters set by the operator. These include following
the edge line of pixels in the 'Outline following' mode or following the
centerline of the selected line width of pixels in the 'Centerline
following' mode. Additionally, TracTrix can be set optionally to create vectors as lines, arcs, circles, polylines, Beziers, NURBS or splines. The original image and desired file type often dictate the mode selected. |
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Definitions |
DXF is one of many vector file formats used for the storage and exchange of CAD drawing data between different CAD software applications. A file containing both raster and vector information. ISO 9000 is an international certification of company quality standards established by The International Standards Organization (ISO), headquartered in Geneva Switzerland. Certification may be required in order to do business in certain industries, in certain countries, with certain companies and many government agencies. There are also other ISO standards with different numbers governing different types of businesses and technologies. Line following software vectorizes interactively. The operator watches as the software tracks along the lines in an image and intervenes if an error is made. This is slower than automatic vectorization but can produce better results in certain types of complex image. Line Following will be supported in a future release of TracTrix in conjunction with other major technical advances. Splines, B-splines, NURBS and Bezier curves A spline or B-spline curve is a blended piece polynomial curve passing near a given set of control points. The blending functions are the type that provide more local control compared to other curves like a Bezier curve. A Bezier is a polynomial curve passing near, but not necessarily through, a set of given points. A Bezier curve represents an equation of an order one less than the number of points being considered. A NURBS (Nonuniform rational B-spline) is a B-spline curve or surface defined by a series of weighted control points and one or more knot vectors. TWAIN is driver software which enables applications software such as TracTrix and other graphics applications to communicate with and drive your scanner. Once you've set up an application to use TWAIN, its presence should be almost invisible to you. Created by Hewlett-Packard, the TWAIN standard is now widely used by other scanner manufacturers. |
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| Topics | ||
| Basic Questions on Paper to CAD conversion |
What's the difference between raster and vector files? Do scans work in a CAD program? What's the difference between pixels and dots per inch? Is a dot a pixel? In image resolution, what's the difference between say, 400 dpi true versus 400 dpi interpolated? How can I use my desktop scanner to create CAD files? Why can't I just edit my raster files and not have to bother taking them to vector? Is there an international standard for vectorization? I've too many drawings to vectorize in-house. How should I choose a bureau? What should I be aware of before I start converting images to CAD? Does high resolution (dpi) assure vector accuracy? What is the difference between accuracy and precision in vectorizing? How come some vector files are bigger than the raster image file? Should this happen? My drawings are already in CAD. How do I publish them electronically around my company? |
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| TracTrix specific questions: | What
is the typical TracTrix Paper to CAD process?
Will TracTrix give me a DWG file? Do I have to use TracTrix to drive my scanner, or will any image file work? What raster and vector formats does TracTrix work with? Is there any way I can use TracTrix without a scanner? What will I save by using TracTrix? What does Tractrix do with text and symbols? Can I just vectorize what I want and not the whole drawing? Does TracTrix despeckle or eliminate "noise"? What does TracTrix do with dashed lines? Is each dash a separate vector? Does TracTrix do orthogonal adjustment? Does TracTrix recognize circles? Can TracTrix show a vector over a raster? Can TracTrix show dimensions in metrics and/or inches? Can TracTrix be set to jump a gap in a line? How many layers can TracTrix put vectors on? How does it do it? Can I use TracTrix without a CAD package? |
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| Definitions | DXF | |
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© 2006 Trix Systems
AB. All rights reserved. |