3D Labels Experiments
###The Problem
Labels in maps are a huge headache, and have been for a long time. There are lots of solutions for 2D mapping, but not so many when you work in 3D, and especially not when your map shifts between 2D and 3D.
###The Experiements
The main trick is a 2D projection of the geometry to place the text, within the canvas. Like a heads-up display layer between the 3D geometry and the camera.
Like this:
In the canvas:
Pros:
-
Fonts don’t need to be resized on zoom
-
No off-screen computations
-
We know exactly what the user sees
Cons:
- Occlusion becomes a problem: Should labels be visible through buildings? Which labels to prioritize, how to prioritize them? For now, these have no occlusion.
Line Labels
- Fit and repeat
float lastSeed = 0.0;
for (int i = 0; i < _anchorLine.size()-1; i++) {
float offset = _anchorLine.getDistances()[i];
float segmentLength = _anchorLine.getDistances()[i+1]-_anchorLine.getDistances()[i];//_anchorLine.getPolars()[i].r;
// Fits?
//
if( segmentLength >= (m_label.width+_maxDistance) ){
// How many times?
int nTimes = segmentLength/(m_label.width+_maxDistance);
// At what distance between each other?
float margin = (segmentLength-m_label.width*(float)nTimes)/((float)nTimes+1.0);
// Add anchors points for seeds
float seed = margin;
for (int i = 0; i < nTimes; i++) {
float potentialSeed = offset + seed ;
if( potentialSeed-lastSeed > _minDistance ){
lastSeed = potentialSeed;
_anchorLine.marks.push_back(lastSeed);
seed += m_label.width+margin;
}
}
} else if ( segmentLength >= m_label.width+_minDistance){
// Only one time
//
float margin = (segmentLength-m_label.width)*0.5;
float potentialSeed = offset + margin ;
if( potentialSeed-lastSeed > _minDistance){
lastSeed = potentialSeed;
_anchorLine.marks.push_back(lastSeed);
}
}
}
- Fade according to tilt angle
float angle = glm::dot(glm::normalize( *m_cameraPos - shapes[0].getCentroid()),glm::vec3(0.,0.,1.));
m_alpha = lerpValue(m_alpha,powf( CLAMP(angle,0.01,1.0), 1.15 ),0.1);
- Curved path following
float angle = PI;
glm::vec3 diff = _anchorLine[0]-_anchorLine[_anchorLine.size()-1];
angle = atan2f(-diff.y, diff.x);
if(angle < PI*0.5 && angle > -PI*0.5){
for (int i = m_text.length()-1; i >=0 ; i--) {
glm::vec3 src = _anchorLine.getPositionAt(_offset);
if(screen.inside(src)){
double rot = _anchorLine.getAngleAt(_offset);
glPushMatrix();
glTranslated(src.x, src.y, src.z);
glScalef(1,-1,1);
glRotated(rot*RAD_TO_DEG, 0, 0, -1);
glScaled(-1, -1, 1);
glTranslated(-m_lettersWidth[i], 0, 0);
glTranslatef(0., -m_label.height*0.5,0.);
m_font->drawString( std::string(1,m_text[i]), m_alpha );
glPopMatrix();
_offset += m_lettersWidth[i];
} else {
break;
}
}
} else {
for (int i = 0; i < m_text.length(); i++) {
glm::vec3 src = _anchorLine.getPositionAt(_offset);
if(screen.inside(src)){
double rot = _anchorLine.getAngleAt(_offset);
glPushMatrix();
glTranslated(src.x, src.y, src.z);
glScalef(1,-1,1);
glRotated(rot*RAD_TO_DEG, 0, 0, -1);
glTranslatef(0., -m_label.height*0.5,0.);
m_font->drawString( std::string(1,m_text[i]), m_alpha );
glPopMatrix();
_offset += m_lettersWidth[i];
} else {
break;
}
}
}
Point Labels
- Project top points
glm::ivec4 viewport;
glm::mat4x4 mvmatrix, projmatrix;
glGetIntegerv(GL_VIEWPORT, &viewport[0]);
glGetFloatv(GL_MODELVIEW_MATRIX, &mvmatrix[0][0]);
glGetFloatv(GL_PROJECTION_MATRIX, &projmatrix[0][0]);
m_anchorPoint = glm::project(m_centroid+m_offset, mvmatrix, projmatrix, viewport);
- Mutual occlusion using depth sort and bounding boxes
bool depthSort(const glmFeatureLabelPointRef &_A, const glmFeatureLabelPointRef &_B){
return _A->getAnchorPoint().z < _B->getAnchorPoint().z;
}
…
std::sort(pointLabels.begin(),pointLabels.end(), depthSort);
for (int i = 0; i < pointLabels.size(); i++) {
if(pointLabels[i]->bVisible){
for (int j = i-1; j >= 0 ; j--) {
if (pointLabels[i]->isOver( pointLabels[j].get() ) ){
pointLabels[i]->bVisible = false;
break;
}
}
}
}
- Occlude line labels with bounding box
double rot = _anchorLine.getAngleAt(_offset);
glmRectangle boundingBox = glmPolyline(m_label,angle).getBoundingBox();
boundingBox.translate(_anchorLine.getPositionAt(_offset+m_label.width*0.5));
bool bOver = false;
for (int i = 0; i < pointLabels->size(); i++ ){
if(pointLabels->at(i)->bVisible){
if( boundingBox.intersects(pointLabels->at(i)->getLabel(0) ) ){
bOver = true;
break;
}
}
}
- Street level point of view
Dependencies
Notes
Compile with linker flags -lcurl