I have perhaps two thousand SVG files, obtained as a result of scanning a number of brochures to greyscale JPG, then batch-binarising them and saving to monochrome TIFF using ScanTailor, then batch-vectorising the TIFFs (using the command-line utility ImageMagick and a quick FOR loop in Fish), and finally resizing/editing them by hand in Inkscape. You can see my workflow heavily favours command-line UNIX utilities; I'll use a graphical tool if necessary, but not for repetitive tasks. If it makes any difference at all, my preferred UNIX distribution is MacOS.
What is left, at the end of this process, is a ~750KB file containing essentially a complete mathematical description of the page. Every printed letter or stroke of the pen has its own path, and (because I didn't use any sort of despeckling algorithm) so does every meaningless artifact (although I made sure to clean up the edges of every page, for workflow reasons).
Most of the scans, though, were imperfect (300 ppi when 600 or 900 ppi would have been better); the binarisation algorithm (the Otsu method) wasn't perfect either, etc. All of the imperfections added up, so in most cases the paths are rather noisy. The path representing the printed capital letter H, for example, needs only eight nodes (corners), or sixteen if it has rounded terminals (ends). I'm willing to accept more than that, because after all the system isn't perfect, but when I see thirty nodes on the H, and it has scalloped sides under magnification, my eyes start to bleed.
I know this isn't anything to worry about when the pages (rendered as PNG) reach the print shop, because the Mark 1 Eyeball will smooth everything out, but I'm too much of a perfectionist to leave it like that.
To solve the problem, I tried selecting all paths in Inkscape with Cmd/A, then using the "simplify path" command by typing Cmd/L. What I expected was that Inkscape would smooth all the paths individually; what resulted was Inkscape smoothing everything collectively into one blurry mess.
I get the result I want if I select path number one and type Cmd/L, then path number two and again Cmd/L, but a representative page has over FOUR HUNDRED paths and this kind of workflow is essentially impracticable.
I know Inkscape has a (very badly documented) command-line mode, and there might perhaps be a script available to do what needs doing, but if it exists somewhere I can't find it. An ideal solution would be to do what I described above, but programmatically (shell script?), then a FOR loop to do it on every file in the directory.
The basic algorithm for path simplification is not that complicated, as long as you do not need to handle curves. So one avenue could be to write a script yourself. The following is an excerpt from a node.js script I have used to simplify polygons/polylines in maps. For geojson files in the size range of up to several MB it would run in 0.1-0.2 seconds on my (old) computer.
The idea is to take the first and last points of a polyline and to measure how far the second point is removed from a line connecting the two. If it is less than a threshold (the smallest deviation from a straight line you will be able to spot), it can be safely removed, and the next middle point can be examined. If not, the point is preserved and further examinations measure the distance from a line from that point to the last.
const sqEpsilon = ... // square (!) of the minimum distance to preserve
// takes a list points in the form [[x,y],...]
function simplifyDP (points) {
const len = points.length;
const markers = new Uint8Array(len);
markers[0] = markers[len - 1] = 1;
simplifyDPStep(points, markers, 0, len - 1);
return markers.reduce((pts, m, i) => {
if (m) pts.push(points[i]);
return pts;
}, []);
}
function simplifyDPStep (points, markers, first, last) {
let maxSqDist = 0, idx;
for (let i = first + 1; i <= last - 1; i++) {
const sqDist = sqDistance(points[i], points[first], points[last]);
if (sqDist > maxSqDist) {
idx = i;
maxSqDist = sqDist;
}
}
if (maxSqDist > sqEpsilon) {
markers[idx] = 1;
simplifyDPStep(points, markers, first, idx);
simplifyDPStep(points, markers, idx, last);
}
}
function sqDistance(p, p1, p2) {
let x = p1[0],
y = p1[1];
const dx = p2[0] - x,
dy = p2[1] - y;
const dot = dx * dx + dy * dy;
if (dot > 0) {
const t = ((p[0] - x) * dx + (p[1] - y) * dy) / dot;
if (t > 1) {
x = p2[0];
y = p2[1];
} else if (t > 0) {
x += dx * t;
y += dy * t;
}
}
const cdx = p[0] - x;
const cdy = p[1] - y;
return cdx * cdx + cdy * cdy;
}
I'm interested in doing a "Solar System" simulator that will allow me to simulate the rotational and gravitational forces of planets and stars.
I'd like to be able to say, simulate our solar system, and simulate it across varying speeds (ie, watch Earth and other planets rotate around the sun across days, years, etc). I'd like to be able to add planets and change planets mass, etc, to see how it would effect the system.
Does anyone have any resources that would point me in the right direction for writing this sort of simulator?
Are there any existing physics engines which are designed for this purpose?
It's everything here and in general, everything that Jean Meeus has written.
You need to know and understand Newton's Law of Universal Gravitation and Kepler's Laws of Planetary Motion. These two are simple and I'm sure you've heard about them, if not studied them in high school. Finally, if you want your simulator to be as accurate as possible, you should familiarize yourself with the n-Body problem.
You should start out simple. Try making a Sun object and an Earth object that revolves around it. That should give you a very solid start and it's fairly easy to expand from there. A planet object would look something like:
Class Planet {
float x;
float y;
float z; // If you want to work in 3D
double velocity;
int mass;
}
Just remember that F = MA and the rest just just boring math :P
This is a great tutorial on N-body problems in general.
http://www.artcompsci.org/#msa
It's written using Ruby but pretty easy to map into other languages etc. It covers some of the common integration approaches; Forward-Euler, Leapfrog and Hermite.
You might want to take a look at Celestia, a free space simulator. I believe that you can use it to create fictitious solar systems and it is open source.
All you need to implement is proper differential equation (Keplers law) and using Runge-Kutta. (at lest this worked for me, but there are probably better methods)
There are loads of such simulators online.
Here is one simple one implemented in 500lines of c code. (montion algorhitm is much less)
http://astro.berkeley.edu/~dperley/programs/ssms.html.
Also check this:
http://en.wikipedia.org/wiki/Kepler_problem
http://en.wikipedia.org/wiki/Two-body_problem
http://en.wikipedia.org/wiki/N-body_problem
In physics this is known as the N-Body Problem. It is famous because you can not solve this by hand for a system with more than three planets. Luckily, you can get approximate solutions with a computer very easily.
A nice paper on writing this code from the ground up can be found here.
However, I feel a word of warning is important here. You may not get the results you expect. If you want to see how:
the mass of a planet affects its orbital speed around the Sun, cool. You will see that.
the different planets interact with each other, you will be bummed.
The problem is this.
Yeah, modern astronomers are concerned with how Saturn's mass changes the Earth's orbit around the Sun. But this is a VERY minor effect. If you are going to plot the path of a planet around the Sun, it will hardly matter that there are other planets in the Solar System. The Sun is so big it will drown out all other gravity. The only exceptions to this are:
If your planets have very elliptical orbits. This will cause the planets to potentially get closer together, so they interact more.
If your planets are almost the exact same distance from the Sun. They will interact more.
If you make your planets so comically large they compete with the Sun for gravity in the outer Solar System.
To be clear, yes, you will be able to calculate some interactions between planets. But no, these interactions will not be significant to the naked eye if you create a realistic Solar System.
Try it though, and find out!
Check out nMod, a n-body modeling toolkit written in C++ and using OpenGL. It has a pretty well populated solar system model that comes with it and it should be easy to modify. Also, he has a pretty good wiki about n-body simulation in general. The same guy who created this is also making a new program called Moody, but it doesn't appear to be as far along.
In addition, if you are going to do n-body simulations with more than just a few objects, you should really look at the fast multipole method (also called the fast multipole algorithm). It can the reduce number of computations from O(N^2) to O(N) to really speed up your simulation. It is also one of the top ten most successful algorithms of the 20th century, according to the author of this article.
Algorithms to simulate planetary physics.
Here is an implementation of the Keppler parts, in my Android app. The main parts are on my web site for you can download the whole source: http://www.barrythomas.co.uk/keppler.html
This is my method for drawing the planet at the 'next' position in the orbit. Think of the steps like stepping round a circle, one degree at a time, on a circle which has the same period as the planet you are trying to track. Outside of this method I use a global double as the step counter - called dTime, which contains a number of degrees of rotation.
The key parameters passed to the method are, dEccentricty, dScalar (a scaling factor so the orbit all fits on the display), dYear (the duration of the orbit in Earth years) and to orient the orbit so that perihelion is at the right place on the dial, so to speak, dLongPeri - the Longitude of Perihelion.
drawPlanet:
public void drawPlanet (double dEccentricity, double dScalar, double dYear, Canvas canvas, Paint paint,
String sName, Bitmap bmp, double dLongPeri)
{
double dE, dr, dv, dSatX, dSatY, dSatXCorrected, dSatYCorrected;
float fX, fY;
int iSunXOffset = getWidth() / 2;
int iSunYOffset = getHeight() / 2;
// get the value of E from the angle travelled in this 'tick'
dE = getE (dTime * (1 / dYear), dEccentricity);
// get r: the length of 'radius' vector
dr = getRfromE (dE, dEccentricity, dScalar);
// calculate v - the true anomaly
dv = 2 * Math.atan (
Math.sqrt((1 + dEccentricity) / (1 - dEccentricity))
*
Math.tan(dE / 2)
);
// get X and Y coords based on the origin
dSatX = dr / Math.sin(Math.PI / 2) * Math.sin(dv);
dSatY = Math.sin((Math.PI / 2) - dv) * (dSatX / Math.sin(dv));
// now correct for Longitude of Perihelion for this planet
dSatXCorrected = dSatX * (float)Math.cos (Math.toRadians(dLongPeri)) -
dSatY * (float)Math.sin(Math.toRadians(dLongPeri));
dSatYCorrected = dSatX * (float)Math.sin (Math.toRadians(dLongPeri)) +
dSatY * (float)Math.cos(Math.toRadians(dLongPeri));
// offset the origin to nearer the centre of the display
fX = (float)dSatXCorrected + (float)iSunXOffset;
fY = (float)dSatYCorrected + (float)iSunYOffset;
if (bDrawOrbits)
{
// draw the path of the orbit travelled
paint.setColor(Color.WHITE);
paint.setStyle(Paint.Style.STROKE);
paint.setAntiAlias(true);
// get the size of the rect which encloses the elliptical orbit
dE = getE (0.0, dEccentricity);
dr = getRfromE (dE, dEccentricity, dScalar);
rectOval.bottom = (float)dr;
dE = getE (180.0, dEccentricity);
dr = getRfromE (dE, dEccentricity, dScalar);
rectOval.top = (float)(0 - dr);
// calculate minor axis from major axis and eccentricity
// http://www.1728.org/ellipse.htm
double dMajor = rectOval.bottom - rectOval.top;
double dMinor = Math.sqrt(1 - (dEccentricity * dEccentricity)) * dMajor;
rectOval.left = 0 - (float)(dMinor / 2);
rectOval.right = (float)(dMinor / 2);
rectOval.left += (float)iSunXOffset;
rectOval.right += (float)iSunXOffset;
rectOval.top += (float)iSunYOffset;
rectOval.bottom += (float)iSunYOffset;
// now correct for Longitude of Perihelion for this orbit's path
canvas.save();
canvas.rotate((float)dLongPeri, (float)iSunXOffset, (float)iSunYOffset);
canvas.drawOval(rectOval, paint);
canvas.restore();
}
int iBitmapHeight = bmp.getHeight();
canvas.drawBitmap(bmp, fX - (iBitmapHeight / 2), fY - (iBitmapHeight / 2), null);
// draw planet label
myPaint.setColor(Color.WHITE);
paint.setTextSize(30);
canvas.drawText(sName, fX+20, fY-20, paint);
}
The method above calls two further methods which provide values of E (the mean anomaly) and r, the length of the vector at the end of which the planet is found.
getE:
public double getE (double dTime, double dEccentricity)
{
// we are passed the degree count in degrees (duh)
// and the eccentricity value
// the method returns E
double dM1, dD, dE0, dE = 0; // return value E = the mean anomaly
double dM; // local value of M in radians
dM = Math.toRadians (dTime);
int iSign = 1;
if (dM > 0) iSign = 1; else iSign = -1;
dM = Math.abs(dM) / (2 * Math.PI); // Meeus, p 206, line 110
dM = (dM - (long)dM) * (2 * Math.PI) * iSign; // line 120
if (dM < 0)
dM = dM + (2 * Math.PI); // line 130
iSign = 1;
if (dM > Math.PI) iSign = -1; // line 150
if (dM > Math.PI) dM = 2 * Math.PI - dM; // line 160
dE0 = Math.PI / 2; // line 170
dD = Math.PI / 4; // line 170
for (int i = 0; i < 33; i++) // line 180
{
dM1 = dE0 - dEccentricity * Math.sin(dE0); // line 190
dE0 = dE0 + dD * Math.signum((float)(dM - dM1));
dD = dD / 2;
}
dE = dE0 * iSign;
return dE;
}
getRfromE:
public double getRfromE (double dE, double dEccentricty, double dScalar)
{
return Math.min(getWidth(), getHeight()) / 2 * dScalar * (1 - (dEccentricty * Math.cos(dE)));
}
It looks like it is very hard and requires strong knowledge of physics but in fact it is very easy, you need to know only 2 formulas and basic understanding of vectors:
Attractional force (or gravitational force) between planet1 and planet2 with mass m1 and m2 and distance between them d: Fg = G*m1*m2/d^2; Fg = m*a. G is a constant, find it by substituting random values so that acceleration "a" will not be too small and not too big approximately "0.01" or "0.1".
If you have total vector force which is acting on a current planet at that instant of time, you can find instant acceleration a=(total Force)/(mass of current planet). And if you have current acceleration and current velocity and current position, you can find new velocity and new position
If you want to look it real you can use following supereasy algorythm (pseudocode):
int n; // # of planets
Vector2D planetPosition[n];
Vector2D planetVelocity[n]; // initially set by (0, 0)
double planetMass[n];
while (true){
for (int i = 0; i < n; i++){
Vector2D totalForce = (0, 0); // acting on planet i
for (int j = 0; j < n; j++){
if (j == i)
continue; // force between some planet and itself is 0
Fg = G * planetMass[i] * planetMass[j] / distance(i, j) ^ 2;
// Fg is a scalar value representing magnitude of force acting
// between planet[i] and planet[j]
// vectorFg is a vector form of force Fg
// (planetPosition[j] - planetPosition[i]) is a vector value
// (planetPosition[j]-planetPosition[i])/(planetPosition[j]-plantetPosition[i]).magnitude() is a
// unit vector with direction from planet[i] to planet[j]
vectorFg = Fg * (planetPosition[j] - planetPosition[i]) /
(planetPosition[j] - planetPosition[i]).magnitude();
totalForce += vectorFg;
}
Vector2D acceleration = totalForce / planetMass[i];
planetVelocity[i] += acceleration;
}
// it is important to separate two for's, if you want to know why ask in the comments
for (int i = 0; i < n; i++)
planetPosition[i] += planetVelocity[i];
sleep 17 ms;
draw planets;
}
If you're simulating physics, I highly recommend Box2D.
It's a great physics simulator, and will really cut down the amount of boiler plate you'll need, with physics simulating.
Fundamentals of Astrodynamics by Bate, Muller, and White is still required reading at my alma mater for undergrad Aerospace engineers. This tends to cover the orbital mechanics of bodies in Earth orbit...but that is likely the level of physics and math you will need to start your understanding.
+1 for #Stefano Borini's suggestion for "everything that Jean Meeus has written."
Dear Friend here is the graphics code that simulate solar system
Kindly refer through it
/*Arpana*/
#include<stdio.h>
#include<graphics.h>
#include<conio.h>
#include<math.h>
#include<dos.h>
void main()
{
int i=0,j=260,k=30,l=150,m=90;
int n=230,o=10,p=280,q=220;
float pi=3.1424,a,b,c,d,e,f,g,h,z;
int gd=DETECT,gm;
initgraph(&gd,&gm,"c:\tc\bgi");
outtextxy(0,10,"SOLAR SYSTEM-Appu");
outtextxy(500,10,"press any key...");
circle(320,240,20); /* sun */
setfillstyle(1,4);
floodfill(320,240,15);
outtextxy(310,237,"sun");
circle(260,240,8);
setfillstyle(1,2);
floodfill(258,240,15);
floodfill(262,240,15);
outtextxy(240,220,"mercury");
circle(320,300,12);
setfillstyle(1,1);
floodfill(320,298,15);
floodfill(320,302,15);
outtextxy(335,300,"venus");
circle(320,160,10);
setfillstyle(1,5);
floodfill(320,161,15);
floodfill(320,159,15);
outtextxy(332,150, "earth");
circle(453,300,11);
setfillstyle(1,6);
floodfill(445,300,15);
floodfill(448,309,15);
outtextxy(458,280,"mars");
circle(520,240,14);
setfillstyle(1,7);
floodfill(519,240,15);
floodfill(521,240,15);
outtextxy(500,257,"jupiter");
circle(169,122,12);
setfillstyle(1,12);
floodfill(159,125,15);
floodfill(175,125,15);
outtextxy(130,137,"saturn");
circle(320,420,9);
setfillstyle(1,13);
floodfill(320,417,15);
floodfill(320,423,15);
outtextxy(310,400,"urenus");
circle(40,240,9);
setfillstyle(1,10);
floodfill(38,240,15);
floodfill(42,240,15);
outtextxy(25,220,"neptune");
circle(150,420,7);
setfillstyle(1,14);
floodfill(150,419,15);
floodfill(149,422,15);
outtextxy(120,430,"pluto");
getch();
while(!kbhit()) /*animation*/
{
a=(pi/180)*i;
b=(pi/180)*j;
c=(pi/180)*k;
d=(pi/180)*l;
e=(pi/180)*m;
f=(pi/180)*n;
g=(pi/180)*o;
h=(pi/180)*p;
z=(pi/180)*q;
cleardevice();
circle(320,240,20);
setfillstyle(1,4);
floodfill(320,240,15);
outtextxy(310,237,"sun");
circle(320+60*sin(a),240-35*cos(a),8);
setfillstyle(1,2);
pieslice(320+60*sin(a),240-35*cos(a),0,360,8);
circle(320+100*sin(b),240-60*cos(b),12);
setfillstyle(1,1);
pieslice(320+100*sin(b),240-60*cos(b),0,360,12);
circle(320+130*sin(c),240-80*cos(c),10);
setfillstyle(1,5);
pieslice(320+130*sin(c),240-80*cos(c),0,360,10);
circle(320+170*sin(d),240-100*cos(d),11);
setfillstyle(1,6);
pieslice(320+170*sin(d),240-100*cos(d),0,360,11);
circle(320+200*sin(e),240-130*cos(e),14);
setfillstyle(1,7);
pieslice(320+200*sin(e),240-130*cos(e),0,360,14);
circle(320+230*sin(f),240-155*cos(f),12);
setfillstyle(1,12);
pieslice(320+230*sin(f),240-155*cos(f),0,360,12);
circle(320+260*sin(g),240-180*cos(g),9);
setfillstyle(1,13);
pieslice(320+260*sin(g),240-180*cos(g),0,360,9);
circle(320+280*sin(h),240-200*cos(h),9);
setfillstyle(1,10);
pieslice(320+280*sin(h),240-200*cos(h),0,360,9);
circle(320+300*sin(z),240-220*cos(z),7);
setfillstyle(1,14);
pieslice(320+300*sin(z),240-220*cos(z),0,360,7);
delay(20);
i++;
j++;
k++;
l++;
m++;
n++;
o++;
p++;
q+=2;
}
getch();
}