Star generator issue

[qwert_e]

When i tried to create stars using star generator, i figured out that stars magnitude (parameter that determine star visibility) does not handled correctly by generator.

Star magnitude is inverse to star brightness, and star generator makes most low-visible stars to be more brighter, so i could not find any familiar constellations on the generated sky.

Can you share the piece of code that handles magnitude on generation?

 

Edited January 24, 2019 by qwert_e

[silent]

qwert_e

Here is the code from Editor1 (UnigineScript):

void create_clicked() {
    
	if(strlen(catalog_el.getText()) == 0) {
		dialogMessageOk(TR("Error"),TR("Select catalog"));
		return;
	}
	
	File file = new File();
	if(file.open(catalog_el.getText(),"rb") == 0) {
		dialogMessageOk(TR("Error"),format(TR("Can't load \"%s\" star catalog\n"),catalog_el.getText()));
		delete file;
		return;
	}
	
	billboards.clearBillboards();
	
	class Star {
		float phi;
		float theta;
		float mag;
		string type;
		Star(float phi_,float theta_,float mag_,string type_) {
			phi = phi_;
			theta = theta_;
			mag = mag_;
			type = type_;
		}
		int operator<(Star s0,Star s1) {
			return (s0.mag > s1.mag);
		}
	};
	
	Star stars[0];
	
	float min_mag = INFINITY;
	float max_mag = -INFINITY;
	
	while(file.eof() == 0) {
		
		string line = file.readLine();
		
		string get_bytes(int from,int to) {
			string ret = "";
			if(strlen(line) < to) return ret;
			for(int i = from; i <= to; i++) {
				ret += format("%c",line[i - 1]);
			}
			return ret;
		}
		
		float rah = float(get_bytes(6,7));
		float ram = float(get_bytes(9,10));
		float ras = float(get_bytes(12,17));
		float decd = float(get_bytes(27,29));
		float decam = float(get_bytes(31,32));
		float decas = float(get_bytes(34,38));
		float mag = float(get_bytes(124,128));
		string type = get_bytes(131,132);
		
		float theta = PI2 * (rah + (ram + ras / 60.0f) / 60.0f) / 24.0f;
		float phi = -PI * (decd + (decam + (decas / 60.0f)) / 60.0f) / 90.0f;
		
		stars.append(new Star(phi,theta,mag,type));
		
		min_mag = min(min_mag,mag);
		max_mag = max(max_mag,mag);
	}
	
	stars.sort();
	
	string types[] = ( 'O' : 0, 'B' : 1, 'A' : 2, 'F' : 3, 'G' : 4, 'K' : 5, 'M' : 6 );
	
	forloop(int i = 0; min(count,stars.size())) {
		Star star = stars[i];
		
		if(types.check(star.type[0]) == 0) continue;
		
		float r = angle * pow((star.mag - min_mag) / (max_mag - min_mag),3.0f);
		
		int atlas_x = clamp(int(16.0f * (max_mag - star.mag) / (max_mag - min_mag)),0,15);
		int atlas_y = types[star.type[0]];
		
		int num = billboards.addBillboard(r,r);
		billboards.setTexCoord(num,vec4(1.0f / 16.0f,1.0f / 8.0f,atlas_x / 16.0f,atlas_y / 8.0f));
		billboards.setAngle(num,engine.game.getRandom(0.0f,360.0f));
		
		float phi = star.phi + latitude * DEG2RAD;
		float theta = star.theta + longitude * DEG2RAD;
		billboards.setPosition(num,vec3(cos(phi) * cos(theta),-cos(phi) * sin(theta),sin(phi)) * radius);
	}
	
	stars.delete();
	
	file.close();
	delete file;
	
	Billboards::update();
}

If you can spot an error here - please let us know :) I belive we used FK5 star catalog from here: http://www-kpno.kpno.noao.edu/Info/Caches/Catalogs/FK5/fk5.html

Thanks!

[qwert_e]

float min_mag = INFINITY;
float max_mag = -INFINITY;

...

min_mag = min(min_mag,mag);
max_mag = max(max_mag,mag);

min_mag must be highest from all mags, min(min_mag,mag) will choose not the highest
and thats below will be more correct:

float min_mag = -INFINITY;
float max_mag = INFINITY;

min_mag = max(min_mag,mag);
max_mag = min(max_mag,mag);

 

in the line: 

float r = angle * pow((star.mag - min_mag) / (max_mag - min_mag),3.0f);

angle should be parameter "angle" in star generator, right?

then if its right, brighest star FK5 257 "SIRIUS A" with magnitude -1.46 will have r = angle*1 
and FK5 1657 with magnitude 8.28 will have r = angle*0

 

catalog should be that in attached files

catalog

Edited January 25, 2019 by qwert_e

[silent]

Thanks, we will take a closer look into this before the next SDK update.

[moroz]

@qwert_e

Hi! If you want get simply stars skymap you should use data\ig\sky_map\textures\stars_c.hdr from IG template as environment texture.