How do I create a dxf spline curve using fitpoints?





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I'm trying to create a spline curve programmatically in a dxf file. I need to use fit points as the curve needs to pass through the specified points. I understand I also need to use control points. Is there a formula to calculate what these should be? It is a closed spline with four fit points.



Thanks in advance!










share|improve this question































    2















    I'm trying to create a spline curve programmatically in a dxf file. I need to use fit points as the curve needs to pass through the specified points. I understand I also need to use control points. Is there a formula to calculate what these should be? It is a closed spline with four fit points.



    Thanks in advance!










    share|improve this question



























      2












      2








      2


      1






      I'm trying to create a spline curve programmatically in a dxf file. I need to use fit points as the curve needs to pass through the specified points. I understand I also need to use control points. Is there a formula to calculate what these should be? It is a closed spline with four fit points.



      Thanks in advance!










      share|improve this question
















      I'm trying to create a spline curve programmatically in a dxf file. I need to use fit points as the curve needs to pass through the specified points. I understand I also need to use control points. Is there a formula to calculate what these should be? It is a closed spline with four fit points.



      Thanks in advance!







      autocad spline dxf






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited Sep 27 '15 at 8:46









      Roman Melnyk

      1,0611720




      1,0611720










      asked Sep 27 '15 at 8:44









      AesculusMaximusAesculusMaximus

      9013




      9013
























          2 Answers
          2






          active

          oldest

          votes


















          4














          I think this is not an easy task. In addition to the control points, you will also need to determine the knots. There is a DXF reader/viewer here (written in C++) which claims to support spline. May be you can find some information by reading the code.



          AutoCAD uses NURBS which are approximated curves (the curve pass only by the first and last points). In the user interface, splines are interpolated (the curve pass by the fit points), so there is a translation which is done when reading/writing a DXF file. If you create a closed point with 4 fit points, you will see there is 7 controls points in the DXF file:



          Fit points vs control points



          Using a polyline to approximate your spline will be easier. Here is a sample of a polyline (L shape starting from 0,0 -> 100, 0 -> 100, 50)



            0
          LWPOLYLINE
          5
          D5
          330
          70
          100
          AcDbEntity
          8
          0
          100
          AcDbPolyline
          90
          3
          70
          0
          43
          0.0
          10
          0.0
          20
          0.0
          10
          100.0
          20
          0.0
          10
          100.0
          20
          50.0


          To compute the position of the control points from the fit points, you can consult this page (§24 & §25). In fact you need to reverse the Casteljau's algorithm (for Bezier curves; I don't know how it works for NURBS).






          share|improve this answer


























          • Yes, thanks Maxence - I've kind of come to the same conclusion. I'm currently trying to use a polyline as you suggested - do you know of any examples that I can see? It looks like as well as the polyline entity, I also need vertex entities.

            – AesculusMaximus
            Sep 27 '15 at 17:07











          • If you write a DXF with a version > R12, you can use LWPOLYLINE instead of POLYLINE, you will not need additional VERTEX entities.

            – Maxence
            Sep 27 '15 at 17:11











          • I downloaded the code referenced. Holy crap is this code unhelpful. Tried to post it here but it hit the stackoverflow character limit. Regardless to say it is full of typos and variables like: AMag, k NP, Mat, Bx, By, Cx, Cy. No explanation for any of these variables is given anywhere.

            – Dustin
            Apr 18 '17 at 2:26



















          1














          While I appreciate this is an old question I thought I'd share my experience. I have found that you can write a spline to a DXF file using only fit points and no control points. I've only done this with open splines, and it might (or probably does) vary with version.



          SECTION
          2
          ENTITIES
          0
          SPLINE
          8
          Outline
          100
          AcDbSpline
          70
          1032
          71
          3
          72
          0
          73
          0
          74
          6
          44
          0.000000001
          11
          33.98654201387437
          21
          0.0
          31
          0.0
          11
          35.68732510673189
          21
          0.36908328878159574
          31
          0.0
          11
          37.37659045005916
          21
          1.0707740721032477
          31
          0.0
          11
          39.04265824154412
          21
          2.0149195037916585
          31
          0.0
          11
          40.67371568762629
          21
          3.1732042281057
          31
          0.0
          11
          42.25786591112497
          21
          4.5302062466715505
          31
          0.0


          Group code 70 bit value 1024 allows for fitting to points. I found this little nugget of information on an AutoCAD forum post. I haven't come across it referenced any where else. A bit value of 1 is Closed spline, and 8 is Planar. My value of 1032 is obviously planar, fitting to points and not closed.



          Group code 74 is the number of fit points.



          Group code 44 is the fit point tolerance.



          Group codes 11, 21, 31 are the x, y, z coordinates of the fit points.



          See reference manual.






          share|improve this answer
























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            2 Answers
            2






            active

            oldest

            votes








            2 Answers
            2






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            4














            I think this is not an easy task. In addition to the control points, you will also need to determine the knots. There is a DXF reader/viewer here (written in C++) which claims to support spline. May be you can find some information by reading the code.



            AutoCAD uses NURBS which are approximated curves (the curve pass only by the first and last points). In the user interface, splines are interpolated (the curve pass by the fit points), so there is a translation which is done when reading/writing a DXF file. If you create a closed point with 4 fit points, you will see there is 7 controls points in the DXF file:



            Fit points vs control points



            Using a polyline to approximate your spline will be easier. Here is a sample of a polyline (L shape starting from 0,0 -> 100, 0 -> 100, 50)



              0
            LWPOLYLINE
            5
            D5
            330
            70
            100
            AcDbEntity
            8
            0
            100
            AcDbPolyline
            90
            3
            70
            0
            43
            0.0
            10
            0.0
            20
            0.0
            10
            100.0
            20
            0.0
            10
            100.0
            20
            50.0


            To compute the position of the control points from the fit points, you can consult this page (§24 & §25). In fact you need to reverse the Casteljau's algorithm (for Bezier curves; I don't know how it works for NURBS).






            share|improve this answer


























            • Yes, thanks Maxence - I've kind of come to the same conclusion. I'm currently trying to use a polyline as you suggested - do you know of any examples that I can see? It looks like as well as the polyline entity, I also need vertex entities.

              – AesculusMaximus
              Sep 27 '15 at 17:07











            • If you write a DXF with a version > R12, you can use LWPOLYLINE instead of POLYLINE, you will not need additional VERTEX entities.

              – Maxence
              Sep 27 '15 at 17:11











            • I downloaded the code referenced. Holy crap is this code unhelpful. Tried to post it here but it hit the stackoverflow character limit. Regardless to say it is full of typos and variables like: AMag, k NP, Mat, Bx, By, Cx, Cy. No explanation for any of these variables is given anywhere.

              – Dustin
              Apr 18 '17 at 2:26
















            4














            I think this is not an easy task. In addition to the control points, you will also need to determine the knots. There is a DXF reader/viewer here (written in C++) which claims to support spline. May be you can find some information by reading the code.



            AutoCAD uses NURBS which are approximated curves (the curve pass only by the first and last points). In the user interface, splines are interpolated (the curve pass by the fit points), so there is a translation which is done when reading/writing a DXF file. If you create a closed point with 4 fit points, you will see there is 7 controls points in the DXF file:



            Fit points vs control points



            Using a polyline to approximate your spline will be easier. Here is a sample of a polyline (L shape starting from 0,0 -> 100, 0 -> 100, 50)



              0
            LWPOLYLINE
            5
            D5
            330
            70
            100
            AcDbEntity
            8
            0
            100
            AcDbPolyline
            90
            3
            70
            0
            43
            0.0
            10
            0.0
            20
            0.0
            10
            100.0
            20
            0.0
            10
            100.0
            20
            50.0


            To compute the position of the control points from the fit points, you can consult this page (§24 & §25). In fact you need to reverse the Casteljau's algorithm (for Bezier curves; I don't know how it works for NURBS).






            share|improve this answer


























            • Yes, thanks Maxence - I've kind of come to the same conclusion. I'm currently trying to use a polyline as you suggested - do you know of any examples that I can see? It looks like as well as the polyline entity, I also need vertex entities.

              – AesculusMaximus
              Sep 27 '15 at 17:07











            • If you write a DXF with a version > R12, you can use LWPOLYLINE instead of POLYLINE, you will not need additional VERTEX entities.

              – Maxence
              Sep 27 '15 at 17:11











            • I downloaded the code referenced. Holy crap is this code unhelpful. Tried to post it here but it hit the stackoverflow character limit. Regardless to say it is full of typos and variables like: AMag, k NP, Mat, Bx, By, Cx, Cy. No explanation for any of these variables is given anywhere.

              – Dustin
              Apr 18 '17 at 2:26














            4












            4








            4







            I think this is not an easy task. In addition to the control points, you will also need to determine the knots. There is a DXF reader/viewer here (written in C++) which claims to support spline. May be you can find some information by reading the code.



            AutoCAD uses NURBS which are approximated curves (the curve pass only by the first and last points). In the user interface, splines are interpolated (the curve pass by the fit points), so there is a translation which is done when reading/writing a DXF file. If you create a closed point with 4 fit points, you will see there is 7 controls points in the DXF file:



            Fit points vs control points



            Using a polyline to approximate your spline will be easier. Here is a sample of a polyline (L shape starting from 0,0 -> 100, 0 -> 100, 50)



              0
            LWPOLYLINE
            5
            D5
            330
            70
            100
            AcDbEntity
            8
            0
            100
            AcDbPolyline
            90
            3
            70
            0
            43
            0.0
            10
            0.0
            20
            0.0
            10
            100.0
            20
            0.0
            10
            100.0
            20
            50.0


            To compute the position of the control points from the fit points, you can consult this page (§24 & §25). In fact you need to reverse the Casteljau's algorithm (for Bezier curves; I don't know how it works for NURBS).






            share|improve this answer















            I think this is not an easy task. In addition to the control points, you will also need to determine the knots. There is a DXF reader/viewer here (written in C++) which claims to support spline. May be you can find some information by reading the code.



            AutoCAD uses NURBS which are approximated curves (the curve pass only by the first and last points). In the user interface, splines are interpolated (the curve pass by the fit points), so there is a translation which is done when reading/writing a DXF file. If you create a closed point with 4 fit points, you will see there is 7 controls points in the DXF file:



            Fit points vs control points



            Using a polyline to approximate your spline will be easier. Here is a sample of a polyline (L shape starting from 0,0 -> 100, 0 -> 100, 50)



              0
            LWPOLYLINE
            5
            D5
            330
            70
            100
            AcDbEntity
            8
            0
            100
            AcDbPolyline
            90
            3
            70
            0
            43
            0.0
            10
            0.0
            20
            0.0
            10
            100.0
            20
            0.0
            10
            100.0
            20
            50.0


            To compute the position of the control points from the fit points, you can consult this page (§24 & §25). In fact you need to reverse the Casteljau's algorithm (for Bezier curves; I don't know how it works for NURBS).







            share|improve this answer














            share|improve this answer



            share|improve this answer








            edited Sep 29 '15 at 9:06

























            answered Sep 27 '15 at 16:20









            MaxenceMaxence

            10.8k34059




            10.8k34059













            • Yes, thanks Maxence - I've kind of come to the same conclusion. I'm currently trying to use a polyline as you suggested - do you know of any examples that I can see? It looks like as well as the polyline entity, I also need vertex entities.

              – AesculusMaximus
              Sep 27 '15 at 17:07











            • If you write a DXF with a version > R12, you can use LWPOLYLINE instead of POLYLINE, you will not need additional VERTEX entities.

              – Maxence
              Sep 27 '15 at 17:11











            • I downloaded the code referenced. Holy crap is this code unhelpful. Tried to post it here but it hit the stackoverflow character limit. Regardless to say it is full of typos and variables like: AMag, k NP, Mat, Bx, By, Cx, Cy. No explanation for any of these variables is given anywhere.

              – Dustin
              Apr 18 '17 at 2:26



















            • Yes, thanks Maxence - I've kind of come to the same conclusion. I'm currently trying to use a polyline as you suggested - do you know of any examples that I can see? It looks like as well as the polyline entity, I also need vertex entities.

              – AesculusMaximus
              Sep 27 '15 at 17:07











            • If you write a DXF with a version > R12, you can use LWPOLYLINE instead of POLYLINE, you will not need additional VERTEX entities.

              – Maxence
              Sep 27 '15 at 17:11











            • I downloaded the code referenced. Holy crap is this code unhelpful. Tried to post it here but it hit the stackoverflow character limit. Regardless to say it is full of typos and variables like: AMag, k NP, Mat, Bx, By, Cx, Cy. No explanation for any of these variables is given anywhere.

              – Dustin
              Apr 18 '17 at 2:26

















            Yes, thanks Maxence - I've kind of come to the same conclusion. I'm currently trying to use a polyline as you suggested - do you know of any examples that I can see? It looks like as well as the polyline entity, I also need vertex entities.

            – AesculusMaximus
            Sep 27 '15 at 17:07





            Yes, thanks Maxence - I've kind of come to the same conclusion. I'm currently trying to use a polyline as you suggested - do you know of any examples that I can see? It looks like as well as the polyline entity, I also need vertex entities.

            – AesculusMaximus
            Sep 27 '15 at 17:07













            If you write a DXF with a version > R12, you can use LWPOLYLINE instead of POLYLINE, you will not need additional VERTEX entities.

            – Maxence
            Sep 27 '15 at 17:11





            If you write a DXF with a version > R12, you can use LWPOLYLINE instead of POLYLINE, you will not need additional VERTEX entities.

            – Maxence
            Sep 27 '15 at 17:11













            I downloaded the code referenced. Holy crap is this code unhelpful. Tried to post it here but it hit the stackoverflow character limit. Regardless to say it is full of typos and variables like: AMag, k NP, Mat, Bx, By, Cx, Cy. No explanation for any of these variables is given anywhere.

            – Dustin
            Apr 18 '17 at 2:26





            I downloaded the code referenced. Holy crap is this code unhelpful. Tried to post it here but it hit the stackoverflow character limit. Regardless to say it is full of typos and variables like: AMag, k NP, Mat, Bx, By, Cx, Cy. No explanation for any of these variables is given anywhere.

            – Dustin
            Apr 18 '17 at 2:26













            1














            While I appreciate this is an old question I thought I'd share my experience. I have found that you can write a spline to a DXF file using only fit points and no control points. I've only done this with open splines, and it might (or probably does) vary with version.



            SECTION
            2
            ENTITIES
            0
            SPLINE
            8
            Outline
            100
            AcDbSpline
            70
            1032
            71
            3
            72
            0
            73
            0
            74
            6
            44
            0.000000001
            11
            33.98654201387437
            21
            0.0
            31
            0.0
            11
            35.68732510673189
            21
            0.36908328878159574
            31
            0.0
            11
            37.37659045005916
            21
            1.0707740721032477
            31
            0.0
            11
            39.04265824154412
            21
            2.0149195037916585
            31
            0.0
            11
            40.67371568762629
            21
            3.1732042281057
            31
            0.0
            11
            42.25786591112497
            21
            4.5302062466715505
            31
            0.0


            Group code 70 bit value 1024 allows for fitting to points. I found this little nugget of information on an AutoCAD forum post. I haven't come across it referenced any where else. A bit value of 1 is Closed spline, and 8 is Planar. My value of 1032 is obviously planar, fitting to points and not closed.



            Group code 74 is the number of fit points.



            Group code 44 is the fit point tolerance.



            Group codes 11, 21, 31 are the x, y, z coordinates of the fit points.



            See reference manual.






            share|improve this answer




























              1














              While I appreciate this is an old question I thought I'd share my experience. I have found that you can write a spline to a DXF file using only fit points and no control points. I've only done this with open splines, and it might (or probably does) vary with version.



              SECTION
              2
              ENTITIES
              0
              SPLINE
              8
              Outline
              100
              AcDbSpline
              70
              1032
              71
              3
              72
              0
              73
              0
              74
              6
              44
              0.000000001
              11
              33.98654201387437
              21
              0.0
              31
              0.0
              11
              35.68732510673189
              21
              0.36908328878159574
              31
              0.0
              11
              37.37659045005916
              21
              1.0707740721032477
              31
              0.0
              11
              39.04265824154412
              21
              2.0149195037916585
              31
              0.0
              11
              40.67371568762629
              21
              3.1732042281057
              31
              0.0
              11
              42.25786591112497
              21
              4.5302062466715505
              31
              0.0


              Group code 70 bit value 1024 allows for fitting to points. I found this little nugget of information on an AutoCAD forum post. I haven't come across it referenced any where else. A bit value of 1 is Closed spline, and 8 is Planar. My value of 1032 is obviously planar, fitting to points and not closed.



              Group code 74 is the number of fit points.



              Group code 44 is the fit point tolerance.



              Group codes 11, 21, 31 are the x, y, z coordinates of the fit points.



              See reference manual.






              share|improve this answer


























                1












                1








                1







                While I appreciate this is an old question I thought I'd share my experience. I have found that you can write a spline to a DXF file using only fit points and no control points. I've only done this with open splines, and it might (or probably does) vary with version.



                SECTION
                2
                ENTITIES
                0
                SPLINE
                8
                Outline
                100
                AcDbSpline
                70
                1032
                71
                3
                72
                0
                73
                0
                74
                6
                44
                0.000000001
                11
                33.98654201387437
                21
                0.0
                31
                0.0
                11
                35.68732510673189
                21
                0.36908328878159574
                31
                0.0
                11
                37.37659045005916
                21
                1.0707740721032477
                31
                0.0
                11
                39.04265824154412
                21
                2.0149195037916585
                31
                0.0
                11
                40.67371568762629
                21
                3.1732042281057
                31
                0.0
                11
                42.25786591112497
                21
                4.5302062466715505
                31
                0.0


                Group code 70 bit value 1024 allows for fitting to points. I found this little nugget of information on an AutoCAD forum post. I haven't come across it referenced any where else. A bit value of 1 is Closed spline, and 8 is Planar. My value of 1032 is obviously planar, fitting to points and not closed.



                Group code 74 is the number of fit points.



                Group code 44 is the fit point tolerance.



                Group codes 11, 21, 31 are the x, y, z coordinates of the fit points.



                See reference manual.






                share|improve this answer













                While I appreciate this is an old question I thought I'd share my experience. I have found that you can write a spline to a DXF file using only fit points and no control points. I've only done this with open splines, and it might (or probably does) vary with version.



                SECTION
                2
                ENTITIES
                0
                SPLINE
                8
                Outline
                100
                AcDbSpline
                70
                1032
                71
                3
                72
                0
                73
                0
                74
                6
                44
                0.000000001
                11
                33.98654201387437
                21
                0.0
                31
                0.0
                11
                35.68732510673189
                21
                0.36908328878159574
                31
                0.0
                11
                37.37659045005916
                21
                1.0707740721032477
                31
                0.0
                11
                39.04265824154412
                21
                2.0149195037916585
                31
                0.0
                11
                40.67371568762629
                21
                3.1732042281057
                31
                0.0
                11
                42.25786591112497
                21
                4.5302062466715505
                31
                0.0


                Group code 70 bit value 1024 allows for fitting to points. I found this little nugget of information on an AutoCAD forum post. I haven't come across it referenced any where else. A bit value of 1 is Closed spline, and 8 is Planar. My value of 1032 is obviously planar, fitting to points and not closed.



                Group code 74 is the number of fit points.



                Group code 44 is the fit point tolerance.



                Group codes 11, 21, 31 are the x, y, z coordinates of the fit points.



                See reference manual.







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered Nov 25 '18 at 6:59









                Dave HardingDave Harding

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