show latitude longitude mouse rotating globe in openFrameworks

main.cpp

#include "ofMain.h"

class ofApp : public ofBaseApp {
public:
    
    ofImage earth;
    ofQuaternion qTo;
    
    void setup() {
        ofBackground(0);
        ofSetFrameRate(30);
        ofDisableArbTex();
        ofEnableDepthTest();
        earth.load("earth.jpg");
    }
    
    void draw() {
        ofSetupScreenOrtho(ofGetWidth(),ofGetHeight(),-1000,1000);
        
        //3D
        ofPushMatrix();
        ofTranslate(ofGetWidth()/2, ofGetHeight()/2);
        float angle;
        ofPoint axis;
        qTo.getRotate(angle,axis);
        ofRotate(angle, axis.x, axis.y, axis.z);
        earth.bind();
        ofPushMatrix();
        ofFill();
        ofSetColor(255);
        ofRotateY(180);
        ofDrawSphere(250);
        ofPopMatrix();
        earth.unbind();

        //red dot
        ofSetColor(255,0,0); //red
        ofDrawSphere(getCartesian(qTo)*250,5);
        ofPopMatrix();
        
        //2D
        float lat = getLatitude(getCartesian(qTo));
        float lon = getLongitude(getCartesian(qTo));
        float x = ofMap(lon,-180,180,0,256);
        float y = ofMap(lat,90,-90,0,128);
        
        ofSetColor(255);
        ofDrawBitmapString("lat: " + ofToString(lat,2),10,ofGetHeight()-40);
        ofDrawBitmapString("lon: " + ofToString(lon,2),10,ofGetHeight()-20);
        ofDisableDepthTest();
        ofSetColor(255);
        earth.draw(0,0,256,128);
        ofFill();
        ofSetColor(255,0,0); //red
        ofDrawCircle(x,y,2);
        ofEnableDepthTest();
    }

    float getLatitude(ofPoint c) { //cartesian
        return ofRadToDeg(-asin(c.y));
    }
    
    float getLongitude(ofPoint c) { //cartesian
        return ofWrapDegrees(ofRadToDeg(-atan2(c.z,c.x))+90, -180, 180);
    }
    
    ofVec3f getCartesian(ofQuaternion q, ofVec3f v = ofVec3f(0,0,1)) {
        ofMatrix4x4 m;
        q.get(m);
        return m*v;
    }
    
    void mouseDragged(int x, int y, int button){
        ofPoint from(ofGetPreviousMouseX(), ofGetPreviousMouseY());
        ofPoint to(ofGetMouseX(), ofGetMouseY());
        from = toSphere(from / ofGetWidth() -.5);
        to = toSphere(to / ofGetWidth() -.5);
        ofPoint axis = from.getCrossed(to);
        qTo *= ofQuaternion(axis.x,axis.y,axis.z,from.dot(to));
    }
    
    ofPoint toSphere(ofPoint v) {  //-0.5 ... +0.5
        float mag = v.x*v.x + v.y*v.y;
        if (mag>1.0f) v.normalize();
        else v.z = sqrt(1.0f - mag);
        return v;
    }
    
};

int main() {
    ofSetupOpenGL(500,500,OF_WINDOW);
    ofRunApp(new ofApp());
}