Parse a DXF file for lines, circles and arcs

[bvdet]

I wrote a script that extracts line and circle data from an Autocad DXF file:

##  GridDXF.py Version 1.02
##  Copyright (c) 2006 Bruce Vaughan, BV Detailing & Design, Inc.
##  All rights reserved.
##  NOT FOR SALE. The software is provided "as is" without any warranty.
########################################################################
'''
parseDXFpts(file_name) - 'file_name' is the name of the DXF file to parse.
                         The function returns a list of lines and a list of circles.
                         All other entities are ignored.
                         Each element of the line list (ptList) is a list of the x, y, z values of the two end points.
                         Each element of the circle list (cirList) is a list of the x, y, z value of the end point and the radius.

formatDXFpts(ptList, cirList) - Returns a formatted string suitable for file method 'write()'.
                                The strings are formatted to be compatible with parametric GridLayout version 1.03 and greater.

Example usage:
    file_name = r'C:\SDS2_7.0\macro\New Versions\Ref\grids.dxf'
    gridFile = r'C:\SDS2_7.0\macro\New Versions\Ref\grid_test.txt'
    f = open(gridFile, 'w')
    f.write(formatDXFpts(*(parseDXFpts(file_name))))
    f.close()

Version 1.00 (5/8/07)
Version 1.01 (5/9/07) -     Skip until ENTITIES section using f.next()
                            Remove unnecessary variable assignments
Version 1.02 (5/10/07) -    Use dict.fromkeys() and f.next() to compile entity data
'''
def parseDXFpts(fn):
    f = open(fn)

    # skip to entities section
    s = f.next()
    while s.strip() != 'ENTITIES':
        s = f.next()

    inLine = False
    inCircle = False

    ptList = []
    cirList = []

    for line in f:
        line = line.strip()
        # In ENTITIES section, iteration can cease when ENDSEC is reached
        if line == 'ENDSEC':
            break
        
        elif inLine == True:
            dd = dict.fromkeys(['10','20','30','11','21','31'], 0.0)
            while line != '0':
                if line in dd:
                    dd[line] = f.next().strip()
                line = f.next().strip()
            ptList.append([[dd['10'], dd['20'], dd['30']], [dd['11'], dd['21'], dd['31']]])
            inLine = False

        elif inCircle == True:
            dd = dict.fromkeys(['10','20','30','40'], 0.0)
            while line != '0':
                if line in dd:
                    dd[line] = f.next().strip()
                line = f.next().strip()
            cirList.append([[dd['10'], dd['20'], dd['30']], dd['40']])
            inCircle = False

        else:
            if line == 'LINE':
                inLine = True
            elif line == 'CIRCLE' or line == 'ARC':
                inCircle = True

    f.close()

    return ptList, cirList

# base must be a tuple or list, not a Point object
def formatDXFpts(ptList, cirList, base=False):
    outList = []
    for pt1, pt2 in ptList:
        if base:
            pt1 = map(str, [i+j for i,j in zip(map(float, pt1), base)])
            pt2 = map(str, [i+j for i,j in zip(map(float, pt2), base)])
        # ExplicitL: 20-0, 20-0, 20-0 : 40-0, 40-0, 40-0
        outList.append('ExplicitL: %s : %s' % (', '.join(pt1), ', '.join(pt2)))
    for pt1, rad in cirList:
        if base:
            pt1 = map(str, [i+j for i,j in zip(map(float, pt1), base)])
        # ExplicitR: 20-0, 20-0, 20-0 : 15-0    
        outList.append('ExplicitR: %s : %s' % (', '.join(pt1), rad))
    return '\n'.join(outList)

if __name__ == '__main__':

    fn = r'C:\SDS2_7.0\macro\New Versions\Ref\grids2.dxf'
    gridStr = formatDXFpts(base=(0.0, -2000.0, -2000.0),*(parseDXFpts(fn)))
    print gridStr
    '''
    file_name = r'C:\SDS2_7.0\macro\New Versions\Ref\grids.dxf'
    gridFile = r'C:\SDS2_7.0\macro\New Versions\Ref\grid_test.txt'
    f = open(gridFile, 'w')
    f.write(formatDXFpts(*(parseDXFpts(file_name))))
    f.close()
    '''

'''
>>> ExplicitL: 9816.68821752379, 9342.150641757189, 0.0 : 5891.694641987371, 7589.498197195453, 0.0
ExplicitL: 13837.65104243732, 8933.988514331103, 0.0 : 14456.10878705126, 5947.569025541323, 0.0
ExplicitL: 13863.97763099647, 8944.937937731237, 0.0 : 14483.88419985993, 5951.522341265071, 0.0
ExplicitL: 15455.83326287129, 6340.472643957712, 0.0 : 14921.10765265826, 6149.932906111864, 0.0
ExplicitL: 16488.77763008338, 6904.236993653539, 0.0 : 15978.35671679392, 6590.049547387251, 0.0
ExplicitL: 3966.563802256045, 10246.06975532415, 0.0 : 18100.41385149004, 10246.06975532415, 0.0
ExplicitR: 16534.87751064366, 4916.545768317483, 0.0 : 380.8099725875799
ExplicitR: 17010.88992108956, 14650.96205330669, 0.0 : 299.1021903913424
>>>
'''

Any suggestions for improvement would be appreciated.

[bartonc]

Thanks, Bruce. I've copied you post to the Articles section.

[Miguel Valenzue]

Hi there. I was looking at your code and was trying to figure out how it works.
What I'm looking to do is to parse out a list of coordinates from a 3D polyline.
My specific question is how to you know where in the dxf file to look for the coordinates?
I've been viewing the dxf file from notepad and can find the coordinates but don't understand how to extract them.
Thanks
Miguel

[bvdet]

Hello Miguel,

In my code, I am looking for 'LINE', 'CIRCLE', and 'ARC' entities. When one of these keywords is encountered, I set a flag for that entity type to True for the next iteration on the file object. You can see in the code elif inLine == True is where a line entity is found. I need data for the end points - left end 10, 20, 30 xyz and right end 11, 21, 31 xyz values. That's all I am interested in, so I create a dictionary with those keys, assign the data to the appropriate key, skip any other unwanted data, and iterate to the next section using file object method next(). You could do something similar looking for POLYLINE entities.