#CLOCKWISE VS COUNTERCLOCKWISE SOFTWARE#

If you write DXF ARC-Data in clockwise order, the ARC appears in other Software wrong, because all well DXF-import interfaces assume that the data is counterclockwise. 'the drawing I have to consider both clockwise and anti-clockwise.'įor WRITING a DXF (blank ascii text, without an DXF-wrapper/programming interface) you have to consider both,īecause you have to calculate the User-input data for the ARC to counterclockwise informations for writing to the DXF file.

'Since I am developing a software to read the DXF file and display'

#CLOCKWISE VS COUNTERCLOCKWISE CODE#

'If I draw the arc in clockwise direction also group code did not appear in the DXF file.'īecause you don't understand coordinatesystems / what the normal vector is (210,220,230) ? To store the ARC-data anti/counter-clockwise. Left to right from roof to bottom, the DXF-definition is You can draw an ARC (in a Coordinatesystem parallel to WCS / with the same direction) 'But one does draw the arc in clockwise direction then what will be the situation? ' Is the highest in terms of trouble-free data exchange.ĭXF is not documented to 100% but for these simple things it is more than enought. These should be used as a benchmark, everyone should do so, and thus the probability of success (if you only read in your own data and you never share these files with others/other software, you can also give an object CIRCLE the look like a rectangle and the definition of a polyline)īut there is only one 'correct' definition for the DXF (per version) and that comes from the company AutoDesk. The 210/220/230 codes are present only for the second one because when they are not present, the extrusion direction is 0,0, (+)1 - see the DXF Reference for an Arc and note the 'optional' under codes 210/220/230 and the description under 210 that 0,0,1 is assumed if not again: Any software can write and interpret (read) DXF data as it pleases. Looking from 'your' underneath, it's still counterclockwise. Note the -1.0 Z coordinate of the extrusion direction for the second Arc - that's downward. The Polyline equivalent/conversion may 'look' clockwise from your point of view, but not from its own. I would word that first sentence quoted above differently - the information about them is always stored as though they were drawn counterclockwise, but they can be drawn clockwise in several ways, at least in terms of the process of defining their geometry in a drawing.

The group codes of extrusion direction '210', '220' and '230' are only shown in data of the 2nd quadrant arc.

The right hand rule is necessary to maintain a consistency for arcs that can freely rotated in wrote: The angles are the same as the first arc (DXF codes 50 and 51) because the arc's angles still use a positive counter clockwise direction but you are viewing it from the opposite direction. In your example, the second arc has a normal pointing in the negative Z direction as indicated by the DXF codes 210, 220, 230 which are 0,0,-1. However, if you were to look at the same arc from the bottom view the Z axis is now pointing away from you and clockwise becomes the apparent positive direction although the arcs true angle direction is CCW when looking down (in the opposite direction) of the normal vector. Thus if you are looking a the top view and the arc lies on the XY plane, the z direction is point to you and positive angles are measure in a CCW direction. That is, if the thumb of your right hand points it the positive direction of the arc's z axis (its normal vector), the curled fingers of the right hand define the positive arc angle direction. It is true that AutoCAD draws arcs in a counterclockwise direction but it could appear to a user that it is clockwise if the user is looking at the arc from the opposite direction! AutoCAD uses a right hand rule for defining arc direction. However if checking an existing arc I found something different. Here is my experiment.' This may verify a clockwise ' IMO the following is a true statement: It is also noticeable that start angle and end angle of 2 arcs are about the same shown above. When I use 'pEdit' command to check the vertexes of the arc (actually it is converted to a polyline segment), I found the arc now is in clockwise direction.

Then use '3drotate' command rotate it 180 degrees by selecting 'Y' axis as rotation axis. I drawn an arc starting at lower-right corner and ending at upper-left corner in 1st quadrant on 'X-Y' plane. However if checking an existing arc I found something different. Here is my experiment. Arcs are drawn in a counterclockwise direction in AutoCAD by default.

Clockwise vs counterclockwise