Entities handles in dxf file

Hello group,

I am writting an application that will create dxf files (2000 format). I
only use the TEXT, LWPOLYLINE and CIRCLE entities. My question is, is there
any type of restrictions for the entities handles? If I have e.g. 200
entities then the handles can be from 100 up too 300 (converted to
hexadecimal)? Are there any rules on how I must create the handles (e.g.
first all the polylines, then circles etc)....

Thank you all

 

Do you *need* handles for your application? If not simply don't write
them...

Unique and easy to use graphics programs
http://www.ransen.com

 

Hello,

If I ommit the handle for the LWPOLYLINE entity, then when I try to load the
dxf, autocad produces an error (Handle missing)...I dont know if there is a
special switch that I must use in order not to create a dxf with the handles
property of the entities

 

Could you use the old style POLYLINE entity instead? Just guessing...


Unique and easy to use graphics programs
http://www.ransen.com

 

Mu guess is that for 2000 format DXF you do need handles.

I have done it and what you do is you assign consecutive numbers to
them. I'll dig out some details tomorrow if you like. Once you've
finished you have to set a variable to the next available handle so
AutoCAD knows where to continue.

hth,
Ben

 

Hello Ben,

In 2000 dxf format the 5 tag (entity handle) cannot be ommited. So what I do
is begin from 1000 and every time I add an entity I add 1 too the previous
handle!!! (I first convert the integer value to hex value).

If you please, I wait for your tips..... BTW, r there any documents on the
internet about dxf files (except from the hlp files provided by autodesk)?

Thank you very much

 

Why does it have to be 2000 format? AutoCAD 2000 can read
R12 format DXF too. Just curious...!

Unique and easy to use graphics programs
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Well, you r right in this matter but I dont know if later versions of
autocad can and will read r12 or 114 dxf formats. Maybe I should change back
to r14 )

 

I am pretty sure that later versions of AutoCAD *can* read older
DXF files.


Unique and easy to use graphics programs
http://www.ransen.com

 

Hi Peter,
here is what I did:

Assume my DXF is loaded in Memo1. I want to insert a text at line
number 'pos', which is just after 'ENTITIES'.
Everytime I add an entity, I set its handle to 'getHandle':

<snippet>
Memo1.Lines.Insert(pos,' 8');
Memo1.Lines.Insert(pos,'AcDbEntity');
Memo1.Lines.Insert(pos,'100');
Memo1.Lines.Insert(pos,getHandle);
Memo1.Lines.Insert(pos,' 5');
Memo1.Lines.Insert(pos,'TEXT');
Memo1.Lines.Insert(pos,' 0');
</snippet>

In the above example, I add the lines back to front, as 'pos' (insert
position) is constant.

And this is what my 'getHandle' does:

function TCopyDialog.getHandle: String;
// find next handle
var
i:Integer;
hand:Integer;
begin
hand:=0;
i:=0;

repeat
if (Memo1.Lines=' 9') and
(Memo1.Lines[i+1]='$HANDSEED') and
(Memo1.Lines[i+2]=' 5')
then hand:=StrToInt('$'+Memo1.Lines[i+3]);
inc(i,2); // we can safely step by 2 in DXFs
until (i>=Memo1.Lines.Count-2) or (hand>0);

// increment $HANDSEED
if hand>0 then Memo1.Lines[i+1]:=IntToHex(hand+1,8);

// return original $HANDSEED
Result:=IntToHex(hand,8);
end;

So 'getHandle' returns the next handle and increments the variable
$HANDSEED at the same time. Look up $HANDSEED in your DXF reference.

hth, Ben

 

The reason why I had to write this format is that I had to read R2000
drawings in, modify if necessary, and write out again. The clients
couldn't be asked to save to R12 DXF.

Also, R12 doesn't support certain entities, this could be another
reason to use a later DXF version. E.g., R12 DXF has no concept of
groups.

hth,
Ben

 

Hello Ben,

Thank you for your replay. Well, first of all I use a template dxf file
which misses the entities section. I start from handle 1000 (I use
IntToHex(handle,2)) and every time I insert an entity I increment handle by
1 (perhaps I should change it by 2 now!). So, according to you, when I am
done with all my entities and just before I save the dxf to my disk I should
change the $HANDSEED to the last handle I used plus 1 (or 2)....

 

No, 1.

No, 1. The skip 1 is for finding a certain entry in a DXF file. You
know how you have one line with '0', next says 'SECTION'. One line
says '8', next says '0'. They come in pairs. So if you are looking for
a particular entry, you can step forward by 2.

$HANDSEED holds the next handle. Please look it up in the online help.

hth, Ben

 

Ok, Ben, my mistake...I got it now. Is there any good handbook about dxf
(besides autotdesk's hlp files)

 

Sorry, you ask the wrong bloke. I don't have any books.
Ben