Re: gEDA-user: pcb GL can't render stretched arcs
Andrew Poelstra: On Thu, Jul 14, 2011 at 08:29:53PM +0200, Karl Hammar wrote: ... Why not just give a warning if width and height is not equal, saying that we don't really support ellipses for the moment, and be done with it. I could, I suppose, but as you mentioned in another post, there are muddled physical units. As that is what I am trying to fix, I need to make changes anyway. Ok. It would be nice if we could at least support the featureset of our file format, while I'm at it. I found in [1]: Given an ellipse: x^2 / a^2 + y^2 / b^2 = 1 where a = greater semiaxis b = lesser semiaxis a = b 0 e = sqrt( a^2 + b^2 ) = linear excentricity = focalpoint semidistance epsilon = e / a = numerical excentricity The equation of the normal to the ellipse: y - y1 = mn * (x - x1), where mn = (a*a * y1) / (b*b * x1) the point on the ellipse = (x1, y1) point on normal = (x, y) The length of the normal (to where it crosses the x-axis): n = b * sqrt(a*a*a*a - e*e * x1*x1) / (a*a) The length of the subnormal (as above but along the x-axis): sn = abs( b*b * x1 / (a*a) ) Hope that it helps. We're here if you need more help. Regards, /Karl Hammar [1] Mathematische formeln Dipl.-Ing. Hans-Jochen Bartsch Veb Fachbuschverlag Leipzig 1974 --- Aspö Data Lilla Aspö 148 S-742 94 Östhammar Sweden +46 173 140 57 ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: pcb GL can't render stretched arcs
Ethan Swint: On 07/14/2011 11:23 PM, Andrew Poelstra wrote: ... To do either one analytically looks like a 4th order equation must be solved. So I am looking for cheap iterative solutions, or approximations, instead. If the point is within the arc's bounding box, transform the point's global coordinates into the arc's local (x: major axis, y: minor axis) coordinates. Ack. Then the distance calculation is a no-brainer. Could you then show us the formula please ? Regards, /Karl Hammar --- Aspö Data Lilla Aspö 148 S-742 94 Östhammar Sweden +46 173 140 57 ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: pcb GL can't render stretched arcs
I am using the polar form of the ellipse given at: http://en.wikipedia.org/wiki/Ellipse#Polar_form_relative_to_center with theta the angle of the point we are checking. (Those cos and sin calculations are easy, just delta-x/len and delta-y/len.) With that I can calculate the distance from the point to an ellipse. Restricting this to an ellipse /segment/ is tricky, since as DJ pointed out, these are not real elliptical arcs, but stretched arcs, so the limiting angles do not correspond directly to actual angles. Adding explicit checks for distance from endpoints would give us an almost-correct solution. There are still pathologies I can think of with arcs whose thickness (or thickness + search radius) is greater than the minor axis, though.. -- Andrew Poelstra Email: asp11 at sfu.ca OR apoelstra at wpsoftware.net Web: http://www.wpsoftware.net/andrew/ ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
gEDA-user: generic symbols en custom pin numbers
As sort of an extension to heterogeneous symbols I wonder how I can make generic symbols, consisting of a set of subsymbols, e.g. a relay coil and several types of contact arrangements like SPST and SPDT, all as separate, little symbols. In my design I would then select the appropriate subparts and assemble a particular arrangement, assign the same refdes to them (probably suffixed by a, b, c or similar in lower case). So far this is simply possible with gschem AFAIK. BUT: relays (to stick to the example) come in (very) many different physical shapes and layouts, each with its own, vendor dependent pin numbering scheme. Therefore, it would be nice to have the possibility to define the pin numbers in the instantiation at the schematic level rather than the fixed pin numbers as defined in the symbol (class level). The slot mechanism is not intented nor useable for this. I have not found any way to promote the pinnumbers to the instantiation or other ways to achieve this. Suggestions more than welcome! thank you, hans ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: pcb GL can't render stretched arcs
Andrew Poelstra: I am using the polar form of the ellipse given at: http://en.wikipedia.org/wiki/Ellipse#Polar_form_relative_to_center with theta the angle of the point we are checking. (Those cos and sin calculations are easy, just delta-x/len and delta-y/len.) With that I can calculate the distance from the point to an ellipse. The shortest line from (x,y) to the ellipse goes through the normal to the ellipses perimeter. The normal does not generally go through the middlepoint of the ellipse. It crosses the line between the center and the nearest focal point. What you get with the above polar calculation is a little bigger value than the true distance, but it could serve as a first aproximation. You could take the minimum of the polar form through the center and through the focus, to get a better value. How accurate an value do we need, would minimum of ±5% and ±0.1mm be ok ? Restricting this to an ellipse /segment/ is tricky, since as DJ pointed out, these are not real elliptical arcs, but stretched arcs, so the limiting angles do not correspond directly to actual angles. ... Isn't that a bug to be fixed instead? Regards, /Karl Hammar --- Aspö Data Lilla Aspö 148 S-742 94 Östhammar Sweden +46 173 140 57 ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: generic symbols en custom pin numbers
Hans Schultz: As sort of an extension to heterogeneous symbols I wonder how I can make generic symbols, consisting of a set of subsymbols, e.g. a relay coil and several types of contact arrangements like SPST and SPDT, all as separate, little symbols. In my design I would then select the appropriate subparts and assemble a particular arrangement, assign the same refdes to them (probably suffixed by a, b, c or similar in lower case). So far this is simply possible with gschem AFAIK. BUT: relays (to stick to the example) come in (very) many different physical shapes and layouts, each with its own, vendor dependent pin numbering scheme. Therefore, it would be nice to have the possibility to define the pin numbers in the instantiation at the schematic level rather than the fixed pin numbers as defined in the symbol (class level). The slot mechanism is not intented nor useable for this. I have not found any way to promote the pinnumbers to the instantiation or other ways to achieve this. I think you currently are restricted to create a seperate footprint file for each of your alternatives. Though it would be nice to be able to pass parameters to the footprint and more or less treat is like a subroutine. Regards, /Karl Hammar --- Aspö Data Lilla Aspö 148 S-742 94 Östhammar Sweden +46 173 140 57 ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: pcb GL can't render stretched arcs
On Fri, Jul 15, 2011 at 09:45:42PM +0200, Karl Hammar wrote: Andrew Poelstra: I am using the polar form of the ellipse given at: http://en.wikipedia.org/wiki/Ellipse#Polar_form_relative_to_center with theta the angle of the point we are checking. (Those cos and sin calculations are easy, just delta-x/len and delta-y/len.) With that I can calculate the distance from the point to an ellipse. The shortest line from (x,y) to the ellipse goes through the normal to the ellipses perimeter. Ohh... of course. Darn. The normal does not generally go through the middlepoint of the ellipse. It crosses the line between the center and the nearest focal point. What you get with the above polar calculation is a little bigger value than the true distance, but it could serve as a first aproximation. You could take the minimum of the polar form through the center and through the focus, to get a better value. How accurate an value do we need, would minimum of ±5% and ±0.1mm be ok ? I suspect that determining an error bound on my method would be just as difficult (mathematically) as finding a different method. There is a fairly informative discussion of this problem on SO: http://stackoverflow.com/questions/2945337/how-to-detect-if-an-ellipse-intersectscollides-with-a-circle The correct methods given there generally require root-solvers, and I don't think we have one right now. We could throw one together or introduce a dependency on, say, the GNU Scientific Library. Since we rarely care about the exact distance, only is it between 0 and Radius it is probable that we could use a bisection method with very few iterations to get an answer. Restricting this to an ellipse /segment/ is tricky, since as DJ pointed out, these are not real elliptical arcs, but stretched arcs, so the limiting angles do not correspond directly to actual angles. ... Isn't that a bug to be fixed instead? It's a design flaw, but fixing it would break existing designs. -- Andrew Poelstra Email: asp11 at sfu.ca OR apoelstra at wpsoftware.net Web: http://www.wpsoftware.net/andrew/ ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: pcb GL can't render stretched arcs
2011/7/16 Andrew Poelstra as...@sfu.ca: There is a fairly informative discussion of this problem on SO: http://stackoverflow.com/questions/2945337/how-to-detect-if-an-ellipse-intersectscollides-with-a-circle I had a look and found one algebraic solution close to the one I have proposed. The correct methods given there generally require root-solvers, Why is the algebraic solution not correct? Since we rarely care about the exact distance, only is it between 0 and Radius it is probable that we could use a bisection method with very few iterations to get an answer. I am convinced we do not need any iterations or equation solvers. We just need to check with the transformed point coordinates in the equations for the two arcs where one is the inner arc and the other is the outer arc where the point radius has been subtrcacted respectively added to the arc lenghts(width, height). If the point intersects the equation for the inner arc is = 0 and the equation for the outer arc is = 0 and since it is not a complete ellipse one need to check that the angle between point and arc centerpoint is within the arcs limiting angles which is not to difficult if the limiting angles are known. Restricting this to an ellipse /segment/ is tricky, since as DJ pointed out, these are not real elliptical arcs, but stretched arcs, so the limiting angles do not correspond directly to actual angles. This is the true problem, if the limiting angles are not know then the problem is unsolvable but I assume there is a way of finding what the real limiting angles are. I have not looked into how they become stretched but there must be a systematic way the stretch transforms the arc. Isn't that a bug to be fixed instead? It's a design flaw, but fixing it would break existing designs. Well, one could still keep the (wrong when stretched) limiting angles and add new paramters to the struct for real angles. Now I also assume from looking at DJ's stretched arc that the axis length along the not stretched direction must also be recalculated. I'll be back. -- Andrew Poelstra Email: asp11 at sfu.ca OR apoelstra at wpsoftware.net Web: http://www.wpsoftware.net/andrew/ ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
