I am implementing a DXF importer, for now I am taking into consideration the HEADER
section and only one variable from it INSUNITS
, TABLES
section only one table BLOCK_RECORD
table, BLOCKS
section, ENTITIES
section (INSERT
, LINE
, LWPOLYLINE
, ARC
, CIRCLE
).
When importing I don't know if I need to take into consideration units, and if I need to, I don't know how exactly to take this into consideration. My file is not imported in the correct way now, it is most likely due to these units as I think I am doing my INSERT
transformations correctly:
EXTRUSIONDIRECTIONTRANSFORMATION *
INSERTIONPOINTTRANSLATION *
ROTATION * SCALING * BASEPOINTTRANSLATION
A file I am importing is imported in the correct way when I remove the BASEPOINTTRANSLATION
, but some other files are not imported in the right way and some parts of the drawing get imported very far away from rest.
It looks to me like the base point of a block is in inches and when I convert it to meters it becomes a bit better. So if someone knows in which order I should do the transformations and how to handle units in DXF files I would be really grateful as I am stuck now.
In the Python ezdxf
package, I do it that way:
M0
= OCS transformation matrix including the scaling of the x-, y- and z-axis; same as OCS transformation matrix * scaling matrixM1
about the extrusion vectorM
= M0
* M1
insert
point
insert
point from the OCS to WCSblock_base_point
by the current matrix M
without translation, the current state of M
doesn't have a translation yet, so a full transformation wouldn't be a problem but a "direction only" transformation is faster in my codeblock_base_point
from the insert
pointM
to (insert.x, insert.y, insert.z, 1)
if row major order, last column if column major order, which is basically M
* translation matrixThe unit scaling can be ignored, the CAD application has to set the correct scaling values to match parent layout units and block reference units in the INSERT
scaling attributes. E.g. if you insert a block with mm-units into a modelspace with m-units, the scaling values of the INSERT
entity have to be 0.001 to convert the millimeters into meters (1mm = 0.001m).