Plotter as digitizer

[Don Y]

Hi,

[I've asked this before -- always with disappointing
results -- but will try again before embarking on
a home-grown solution]

(Many? All?) HP pen plotters have the capability of
being used as oversized digitizers. The pen holder is
replaced with a "sight" (essentially, an optical pipe)
and the joystick used to slew the paper/sight to each
location of interest, etc.

The location of the paper/sight is then reported to
the external device.

I have many oversized (D&E) drawings that I would like to
digitize and discard. The first idea that came to mind
was to do this by replacing the pointing device in an
AutoCAD instance as this is most intuitive.

But, I find it hard to believe that someone hasn't
already done something to exploit this capability.

Or, am I the only soul who still has pen plotters? :>

I suppose I could also just write a little piece of code
to gobble up incoming data and scribble it to a file -- which
can later be imported to <whatever>. But, this separates the
"data collection" from the *use* which can be tedious with
lots of spatial data stripped of its *context*!

(sigh) I'll try google, yet again...

Thx,
--don

 

[Winston]

Hi,

[I've asked this before -- always with disappointing
results -- but will try again before embarking on
a home-grown solution]

Could you use a large format document scanner and
capture your drawings to pdf?

--Winston

 

[Don Y]

Hi Winston,

[I've asked this before -- always with disappointing
results -- but will try again before embarking on
a home-grown solution]

Could you use a large format document scanner and
capture your drawings to pdf?

It would have to be a *really* big scanner (or, a photographic
process) as E size drawings would humble my *B* size scanner!

And, I suspect it would be hard to extract the geometric
data from the PDF -- unless I wrote something to analyze the
image contained therein, itself.

(I.e., I want to be able to *use* the data represented
in the drawings, not just "view" it)

 

[Winston]

Hi Winston,

Hey, Don.

(I.e., I want to be able to *use* the data represented
in the drawings, not just "view" it)

Ah.

Large format scanners are available:
http://www.scanners4cad.com/

....or DAGS "E size scanner"

Perhaps your local Kinko's can rent
you one for reasonable money.

From there you need a program to convert
it's output to a DXF.

And a *lot* of cleanup after that!

--------OR-----------

There are service bureaus that will manually
capture your print to a CAD file for $75.
an hour!

--------OR-----------

You can be sure there is a talented young
person around who would leap at the chance
to make $50 each to manually capture each
of your prints, after a few free tutorial
sessions.

--Winston

 

[Rich Grise]

[I've asked this before -- always with disappointing
results -- but will try again before embarking on
a home-grown solution]

(Many? All?) HP pen plotters have the capability of
being used as oversized digitizers. The pen holder is
replaced with a "sight" (essentially, an optical pipe)
and the joystick used to slew the paper/sight to each
location of interest, etc.

The location of the paper/sight is then reported to
the external device.

I have many oversized (D&E) drawings that I would like to
digitize and discard. The first idea that came to mind
was to do this by replacing the pointing device in an
AutoCAD instance as this is most intuitive.

But, I find it hard to believe that someone hasn't
already done something to exploit this capability.

Or, am I the only soul who still has pen plotters? :>

I suppose I could also just write a little piece of code
to gobble up incoming data and scribble it to a file -- which
can later be imported to <whatever>. But, this separates the
"data collection" from the *use* which can be tedious with
lots of spatial data stripped of its *context*!

(sigh) I'll try google, yet again...

It sounds like just making a bitmap isn't good enough; you want
to maintain connectivity. If I've guessed right, then the only
thing I can really think of is to shove your probe around by
hand, and trace the wires; this would only work if your plotter
can actually read back its pen's position, and you have some
SW following it that understands connections.

Other than that, I've got nothing but political propaganda, but
that gets me shunned. ;-)

Good Luck!
Rich

 

[Don Y]

Hi Winston,

Ah.

Yes. E.g., the plans for the house would be helpful to have
in CAD as it would make an easy job of determining how many
sheets of wallboard I will need to hang, how many (floor)
tiles to lay, etc. Much easier (and safer!) than trusting a
tape rule :-/ (damn things *lie* every time I use one!)

Also, there are things you can do with a dimensionally accurate
drawing that are *really* tedious to do, otherwise. E.g.,
deciding where to lay the *first* floor tile to yield the best
"pattern" throughout the house!

Large format scanners are available:
http://www.scanners4cad.com/

...or DAGS "E size scanner"

Gack! I'm already grumbling about having the damn plotters
taking up space in the garage -- and you want me to add
another dust catcher? :>

Perhaps your local Kinko's can rent
you one for reasonable money.

From there you need a program to convert
it's output to a DXF.

And a *lot* of cleanup after that!

Yes. And, never knowing if an error hasn't crept in.

There are service bureaus that will manually
capture your print to a CAD file for $75.
an hour!

You can be sure there is a talented young
person around who would leap at the chance
to make $50 each to manually capture each
of your prints, after a few free tutorial
sessions.

<frown>

I was thinking about this on my evening walk and
think I have come up with a solution -- when the
problem defies solution, *change* the problem! :>

I can, instead, write an *emulator* that allows the
plotter to masquerade as a conventional digitizing
tablet (e.g., a Kurta, Calcomp, Summagraphics, etc.).
This allows me to use the plotter with a variety
of software programs instead of just, e.g., AutoCAD.

The issue then becomes one of finding the digitizer
that is supported by the "most" tools that I am
likely to use (so I don't have to write more than
one "emulator")

 

[Don Y]

Maybe I don't fully understand the problem....
Could you hang the plots on a wall and photograph them?
Then, post-process those image files to get what you want?

What is it that you want to extract from the paper drawings, that must
make it into your electronic copy?
If accurate dimensions, you should be able to scale the photograph,
assuming a few variables fall into place.

Then, how do I get the *images* into, e.g., a CAD program?
I.e., for the house plans, once in AutoCAD, I could lay a
pattern of floor tiles onto it and use the "walls" to
"trim" them. I could touch the corners of each room and
have it report the area of the polygon. Etc.

 

[Winston]

Hi Winston,



Yes. E.g., the plans for the house would be helpful to have
in CAD as it would make an easy job of determining how many
sheets of wallboard I will need to hang, how many (floor)
tiles to lay, etc. Much easier (and safer!) than trusting a
tape rule :-/ (damn things *lie* every time I use one!)

I have *exactly* the same tapes.

(...)

Gack! I'm already grumbling about having the damn plotters
taking up space in the garage -- and you want me to add
another dust catcher? :>

Better you than me.

Yes. And, never knowing if an error hasn't crept in.

That is true for any approach one takes.
One could find the disk files that one
created initially.....

<frown>

Just a thought.

(...)

My favoritest CAD program in the world, Rhino3D
allows me to place a bitmap as 'wallpaper' on
the screen.

http://www.rhino3d.com/4/help/Commands/BackgroundBitmaps.htm

I have used that capability to capture parts
I've scanned by tracing CAD lines over the
lines I see in the bitmap.

You see where I'm headed with that?

--Winston

 

[Martin Riddle]

Then, how do I get the *images* into, e.g., a CAD program?
I.e., for the house plans, once in AutoCAD, I could lay a
pattern of floor tiles onto it and use the "walls" to
"trim" them. I could touch the corners of each room and
have it report the area of the polygon. Etc.

Have someone scan it.
<http://www.cadcam.org/>

Get a quote and see what it costs.

Cheers

 

[John S]

Other than that, I've got nothing but political propaganda, but
that gets me shunned. ;-)

Good Luck!
Rich

Well, not yet. But we still have hope.

 

[Don Y]

Hi Winston,

I have *exactly* the same tapes.

I have learned that a length of *wire* (NOT "string" -- string
stretches too much!) makes a better "ruler":
"I need to cut the board to *this* length..."

:>

That is true for any approach one takes.
One could find the disk files that one
created initially.....

I wasn't the architect that drew the house plans! :>

My favoritest CAD program in the world, Rhino3D
allows me to place a bitmap as 'wallpaper' on
the screen.

http://www.rhino3d.com/4/help/Commands/BackgroundBitmaps.htm

I have used that capability to capture parts
I've scanned by tracing CAD lines over the
lines I see in the bitmap.

You see where I'm headed with that?

I wonder how reliable that would be trying to scale a
50+ inch drawing to correspond with an on-screen image...

I'm currently looking at various tablets with an
eye towards the simplest/cleanest implementation
(e.g., any "smarts" in the tablet would have to be
emulated correctly in anything I write). OTOH,
that might make the design easier to implement
*if* I allow the transactions to drive the emulation
instead of forcing the emulation to fit a specific
model/configuration.

E.g., scan the input file and let it define the
"size" of the (virtual) tablet that I am defining.

 

[Winston]

Hi Winston,



I have learned that a length of *wire* (NOT "string" -- string
stretches too much!) makes a better "ruler":
"I need to cut the board to *this* length..."

:>

And I have learned that sometimes I work faster and
more accurately when I *don't* measure.

Jig for cutting fence boards instead of measuring

Holding a board up to where it needs to go and
scribing a cut line against where it needs to stop.

(...)

I wasn't the architect that drew the house plans! :>
OIC

(...)


I wonder how reliable that would be trying to scale a
50+ inch drawing to correspond with an on-screen image...

It is down to scanner resolution and careful
alignment.

Just now for larfs, I created a rectangle measuring
100 feet by 100 feet so that I could zoom in to
find out how much resolution I had for the minimum
feature size for an underlying drawing.

It ran out of gas at about 14 *pico inches*.
(note that the underlying bitmap would look like
one enormous pixel near x=0 Y=0 at this
magnification.)

I *love* Rhino3D.

I'm currently looking at various tablets with an
eye towards the simplest/cleanest implementation
(e.g., any "smarts" in the tablet would have to be
emulated correctly in anything I write). OTOH,
that might make the design easier to implement
*if* I allow the transactions to drive the emulation
instead of forcing the emulation to fit a specific
model/configuration.

E.g., scan the input file and let it define the
"size" of the (virtual) tablet that I am defining.

At the end of the day, it will be you peering
through crosshairs on a microscope attached to
your pen holder, laboriously capturing vectors.
You are made of stout stuff, Don. I couldn't
do it. My back is sending me warning pains
just thinking about it.

I would cheat and make a scanner do the hard
work.

--Winston

 

[Don Y]

Hi Winston,

And I have learned that sometimes I work faster and
more accurately when I *don't* measure.

Jig for cutting fence boards instead of measuring

Holding a board up to where it needs to go and
scribing a cut line against where it needs to stop.

Yup. Though even this way you have to remember that
the pen won't mark *exactly* where the cut should be.

It is down to scanner resolution and careful
alignment.

Just now for larfs, I created a rectangle measuring
100 feet by 100 feet so that I could zoom in to
find out how much resolution I had for the minimum
feature size for an underlying drawing.

But you created that rectangle *in* the CAD program?
I.e., using *it's* notion of what a "foot" might be.

In my case, I have a drawing drawn to *some* scale
which has to be *mapped* into a corresponding scale
inside the CAD program.

It ran out of gas at about 14 *pico inches*.
(note that the underlying bitmap would look like
one enormous pixel near x=0 Y=0 at this
magnification.)

I *love* Rhino3D.


At the end of the day, it will be you peering
through crosshairs on a microscope attached to
your pen holder, laboriously capturing vectors.

No, the "sight" is a ~1/4" diameter "pipe" made of lexan.
All it really does is bring the image that is on the
paper "under" the pen (sight) up to a point where it is
visible to the user.

Recall that architectural drawings are lots of right angles
(typically... there are a few exceptions, here) so the
points that you are digitizing tend to be offset along
one axis -- or the other -- from each other (no diagonals).

I have to think hard about how I want to handle the
*schematics*, though. It may be simpler just to redraw

You are made of stout stuff, Don. I couldn't
do it. My back is sending me warning pains
just thinking about it.

*Big* plotter. It stands ~4 ft tall so the sight is
pretty much where you can just look at it casually.

I would cheat and make a scanner do the hard
work.

There is a large Calcomp tablet in a local auction
next week. If I can figure out an easy way to get
it home, I may opt for that, instead.

 

[[email protected]]

Architectural drawings aren't the exact dimensions of the finished
building. I've seen walls that were off by more than a foot from the
blueprints. Sometimes there are 'As Built' drawings to match the actual
construction, but they are rare.

Not to mention out-of-square (or plumb) walls. I doubt there is an "as built"
drawing of many of these.

Architectural drawings don't show you were the studs are in the
framing, so you can end up using extra sheets of drywall to avoid more
tape & mud on joints.

When I do a room, I do add these to the CAD drawings. It helps later.

 

[[email protected]]

One place I worked, the owner built an addition. One wall ended up
16" shorter than the opposite because he measured the stakes wrong, then
poured the foundation out of square.

I hope it was a "modern" house. At least he saved a stud. ;-)

 

[Winston]

Hey there, Don!

Hi Winston,



Yup. Though even this way you have to remember that
the pen won't mark *exactly* where the cut should be.

Yup. It will measure 'long' for 'outside' measurements.

* For me that usually means a small overlap
if I cut very close to the line. This is good.

* The scribed line will echo any angular displacement
in the joint. Sometimes a 90 degree cut will not
rhyme very well against a twisted beam.

(...)

But you created that rectangle *in* the CAD program?
I.e., using *it's* notion of what a "foot" might be.
Yes.

In my case, I have a drawing drawn to *some* scale
which has to be *mapped* into a corresponding scale
inside the CAD program.

Trivial. You can move and scale the bitmap in
Rhino3D to match any reference dimension on your
drawing. Ferinstance, I have a 70' long fence
section on my property. I draw a "70'" long line
in the correct orientation on my drawing and move
(and scale) the 'plan' bitmap until the image of
the fence section equals my "70'" reference line.

Now I know my reference drawing and my CAD package
agree what a 'foot' is, to within an acceptable error.

(...)

No, the "sight" is a ~1/4" diameter "pipe" made of lexan.
All it really does is bring the image that is on the
paper "under" the pen (sight) up to a point where it is
visible to the user.

That is better, but still not terribly fast, accurate
and easy, IMHO.

Recall that architectural drawings are lots of right angles
(typically... there are a few exceptions, here) so the
points that you are digitizing tend to be offset along
one axis -- or the other -- from each other (no diagonals).

The error using the scanner at 600 dpi is about +- 0.003".
Multiply that by the reduction scale to reveal the real-
life error. Could you hold +-0.003" using the plotter
digitizer jig? I am sure that I couldn't, though it
is easy to do, all day using a scanned bitmap in Rhino3D.

I have to think hard about how I want to handle the
*schematics*, though. It may be simpler just to redraw
everything using <whatever> symbol library is convenient
(instead of trying to reproduce the drawings AS IS)

I concur, especially if you have a second-level data
extraction process that creates a Bill Of Materials.

(...)

There is a large Calcomp tablet in a local auction
next week. If I can figure out an easy way to get
it home, I may opt for that, instead.

Do you have a smaller digitizer tablet available?
It would be highly interesting to do a 'trial run'
using hardware on hand.

I can move a sandpile with only a teaspoon, but I can do
it much faster and more easily with a shovel.
Discovering that early in the process can save me a
lot of time and sweat.



--Winston

 

[Winston]

Fred Bloggs wrote:

(...)

I bet you could reproduce that drawing in CAD in less time than it
takes you to digitize with the plotter- no contest.

This assumes that everything on the source drawing is dimensioned
completely and there is no need to scale the drawing to extract
the missing data.

I don't believe that is the case here.

--Winston

 

[Don Y]

Depending on where home is for you, I might be closer.

Hard to be much closer than the "local auction" (probably
6 miles, as the crow flies) :>

I have an HP DraftPro Plus (E-Size, 8-pen carosel plotter) plus
several hundered unused pens I would glady part with for the right
price.
And by that, I would suggest half the price of a new wide-angle 35mm
lens, or about $200.

I've already got three large-format plotters. The Calcomp *tablet*
would allow me to "not solve" the "plotter as digitizer" problem.

Mine does not have (what I assume is an optional) digitizer pen, but
maybe they are available.
BTW - This plotter is in great shape, with probably less than 300
hours on it total.
Parallel port interface.

Hmmm... I thought all HP's were serial/HPIB (?). I don't know how
you could provide the digitizer functionality using a (conventional)
parallel port...

 

[Don Y]

Hi Michael,

Architectural drawings aren't the exact dimensions of the finished
building.

Correct. They represent the architects *intent*. They don't
represent the inevitable screw ups!

In our case, the plans aren't even for this *exact* house but,
rather, for another "identical floorplan" (different elevation)
in the neighborhood. E.g., they don't show the living room
as sunken, don't show the "frontier style" roof, don't show
the fireplace, etc.

There are also obvious errors *in* the original drawings -- like
the RO for the kitchen window extending *below* the height of
the adjoining countertop! (oops!)

I've seen walls that were off by more than a foot from the
blueprints. Sometimes there are 'As Built' drawings to match the actual
construction, but they are rare.

Architectural drawings don't show you were the studs are in the
framing, so you can end up using extra sheets of drywall to avoid more
tape& mud on joints.

Yes, and dimensions alone won't help you decide *exactly* how
many 8, 10, 12 or 16 ft sheets you'll need. It's an
*estimating* tool.

Until I saw the "professional" plans (i.e., more than just my
*sketches* of the floorplan), I had never considered how significant
*where* I laid the first tile would be! Having seen it, now, I
will spend a good deal more time evaluating potential layouts
before placing that tile as it has a significant impact on the
final appearance of the tile in total.

This is *much* easier to do with a scaled CAD rendering than
"sketches"!

 

[Don Y]

Hi Winston,

Yup. It will measure 'long' for 'outside' measurements.

* For me that usually means a small overlap
if I cut very close to the line. This is good.

* The scribed line will echo any angular displacement
in the joint. Sometimes a 90 degree cut will not
rhyme very well against a twisted beam.

Yes, I've learned many of these lessons the hard way :<
I installed blocking in the kitchen walls off of which
to hang the new cabinets. Nice square cuts with the
chop saw. Yet, few of them "fit" properly due to
the twists and "non-square" placements of the studs.

Trivial. You can move and scale the bitmap in
Rhino3D to match any reference dimension on your
drawing. Ferinstance, I have a 70' long fence
section on my property. I draw a "70'" long line
in the correct orientation on my drawing and move
(and scale) the 'plan' bitmap until the image of
the fence section equals my "70'" reference line.
OK.

Now I know my reference drawing and my CAD package
agree what a 'foot' is, to within an acceptable error.


That is better, but still not terribly fast, accurate
and easy, IMHO.

Recall these are just *walls*. Walls that I am intimately
familiar with! :> Find a corner. "ENTER" it. Slew the
pen along the wall to the next "corner". ENTER that.
Lather, rinse, repeat.

You're just walking along the surfaces of the house interior
(then exterior) so its really just a couple of bizarre
polygons.

Once all the points are ENTERed, go back and figure out
if you missed any "features". E.g., we have one partial
wall that separates the living room from dining room.
Not load bearing but, rather, present for "artistic purposes"
to break the sight line (we visited another house with
similar floorplan where this wall had been removed and the
"feel" of the house was decidedly less friendly/intimate).

The error using the scanner at 600 dpi is about +- 0.003".
Multiply that by the reduction scale to reveal the real-
life error. Could you hold +-0.003" using the plotter
digitizer jig? I am sure that I couldn't, though it
is easy to do, all day using a scanned bitmap in Rhino3D.


I concur, especially if you have a second-level data
extraction process that creates a Bill Of Materials.

I think the bigger problem would be finding a symbol library
that was consistent with the symbols that I used in the
original schematics. Note that it not only has to draw the
components the same way but, also, the relative placements
of the various connections to those components must be
correct/consistent.

Do you have a smaller digitizer tablet available?
It would be highly interesting to do a 'trial run'
using hardware on hand.

I have a couple of 12x12 and 12x18 tablets on hand.
These will work well in AutoCAD, for example, -- but,
only for drawings of those sizes (I regularly use
the 12x12 with autocad for this sort of thing).

The Calcomp tablet in question is at least D size
(this is what would make fetching it home difficult)
so it would allow me to just mount the drawings and
go to it! It would take up a sh*tload of room, here,
but could double as a drafting table when not in
use as a digitizer.

I can move a sandpile with only a teaspoon, but I can do
it much faster and more easily with a shovel.
Discovering that early in the process can save me a
lot of time and sweat.

Just cover it up with *dirt* and buy *new* sand for the
"relocated pile"! :>