interpolating coordinates from a poly line other than the input points

Hi

I have coordinates for an aerofoil which I put into Autocad and plotted using pline. I have 52 points, what I want is to have more points on the aerofoil, i.e interpolate. I can probably create more points by averaging two adjacent y-points and two adjacent x-points but it would be much better if Autocad did this

the LIST command only gives the points i put in the program.

If you are working on a polyline it is probably a good idea to CLOSE it. In 2012 if you first SELECT the polyline with a left click, you will see a great many grips. On each segment, between the vertices you will see an additional grip, which can be used for converting to an arc, or adding another vertex. If you hover briefly over any of the grips you will see a 3 item drop down menu which includes ADD VERTEX. You can very easily add as many vertices as you wish. I am not sure if this was in 2011 or not. It is a real improvement for grip operations and manipulation. In the attachment you will see a group of vertices which I added to one straight segment of this polyline.

I just checked, and this feature is also available in 2011. The 3 options on the drop down are STRETCH, ADD VERTEX and CONVERT TO ARC. These are really helpful options which can be used on every single grip on a polyline.

I assume you got those points from a table. You could search on the net the formula used to generate the profile. The formulas are available, just to identify the parameters could take you some time. Once you got it (and checked) you can generate as many points within a profile as you wish.

The plot thickens, both figuratively and literally.

If you start by plotting your points onto a spline things really get interesting,and easy.

command PEDIT>ENTER

multiple, select the spline.

convert to POLYLINES, yes. join,

adjust the value in the SPECIFY PRECISION FOR SPLINE CONVERSION.

As shown in the attachment I reset the default value of 10 to 40, and shizzam! All the interpolated points I would expect anybody would ever need, and between each two vertices is yet another drop down menu offering the chance to add another vertex, stretch or convert to curve.

If you start by plotting your points onto a spline things really get interesting,and easy.

command PEDIT>ENTER

multiple, select the spline.

convert to POLYLINES, yes. join,

adjust the value in the SPECIFY PRECISION FOR SPLINE CONVERSION.

The only trouble with using a spline is shown beautifully in your first picture. The curve does NOT pass through the plotted points.

There does not seem to be much point in calculating all the coordinates, and then plotting a curve which misses all the carefully calculated points

You would do much better by drawing a straight line polyline between each point successively, and then use the Fit option with PEDIT. This puts arcs between the plotted points, so you do not need any extra points to make a curve, AutoCAD does it for you

Eldon, hard to fault that logic. I've not used PEDIT much. I was just struck by how on the spline it could interpolate so many points so easily.

One thing about Autocad, there is never any shortage of new skill sets to hone and things to learn. Thanks for the elucidation.

Thank you all for your help. I got it sorted it out.

If you hover briefly over any of the grips you will see a 3 item drop down menu which includes ADD VERTEX. You can very easily add as many vertices as you wish.

adjust the value in the SPECIFY PRECISION FOR SPLINE CONVERSION.

As shown in the attachment I reset the default value of 10 to 40, and shizzam! All the interpolated points I would expect anybody would ever need, and between each two vertices is yet another drop down menu offering the chance to add another vertex, stretch or convert to curve.

Adding vertices manually worked but it takes a long time to make more points, e.g get 100 points from 50! and sometimes adding a vertex will ruin the curve.

However, using spline and changing the precision worked great, only thing is for this case there is something wrong with the coordinates in the lower surface of the leading edge, the curve is not smooth and using the spline will make it even less smooth.

I found a website which gives enough coordinates for aerofoils but I will be using the spline method if i needed it.

I assume you got those points from a table. You could search on the net the formula used to generate the profile. The formulas are available, just to identify the parameters could take you some time. Once you got it (and checked) you can generate as many points within a profile as you wish.

Yes I saw formulas for different aerofoils, the NACA aerofoils are usually given with a formula but not all do have.

You would do much better by drawing a straight line polyline between each point successively, and then use the Fit option with PEDIT. This puts arcs between the plotted points, so you do not need any extra points to make a curve, AutoCAD does it for you

I need more coordinates for simulation purposes. I also need to use Autocad to see if the shape fits in a template or not (for manufacturing) but the points I already have are sufficient for just plotting.

Thanks again

What about DIVIDE then ddptype

BIGAL wins! Poetry in motion.

The only trouble with using a spline is shown beautifully in your first picture. The curve does NOT pass through the plotted points.

 

There does not seem to be much point in calculating all the coordinates, and then plotting a curve which misses all the carefully calculated points

 

 

You would do much better by drawing a straight line polyline between each point successively, and then use the Fit option with PEDIT. This puts arcs between the plotted points, so you do not need any extra points to make a curve, AutoCAD does it for you

Splines can pass through the points, you just need to change its properties. Heidi Hewitt explains it well here: http://heidihewett.blogs.com/my_weblog/2010/05/spline-methods-in-autocad-2011.html

Splines can pass through the points, you just need to change its properties.

I didn't think that applied to spline fit polylines - only to splines that are drawn with the Spline command to begin with. There used to be a difference

I didn't think that applied to spline fit polylines - only to splines that are drawn with the Spline command to begin with. There used to be a difference

You're right there eldon, but I thought the OP could join the points with a spline at the begining rather than a polyline. Then using PEDIT, as DADGAD said in #4, it converts the spline back to a polyline which sill passes through all of the points and allows the precision to be changed.