/**
* Create a set of points on the heightfield for a 2D polyline by draping the point onto
* the surface.
*
* \param line The 2D line to drape, in Earth coordinates.
* \param fSpacing The approximate spacing of the surface tessellation, used to
* decide how finely to tessellate the line.
* \param fOffset An offset to elevate each point in the resulting geometry,
* useful for keeping it visibly above the ground.
* \param bInterp True to interpolate between the vertices of the input
* line. This is generally desirable when the ground is much more finely
* spaced than the input line.
* \param bCurve True to interpret the vertices of the input line as
* control points of a curve. The created geometry will consist of
* a draped line which passes through the control points.
* \param bTrue True to use the true elevation of the terrain, ignoring
* whatever scale factor is being used to exaggerate elevation for
* display.
* \param output Received the points.
* \return The approximate length of the resulting 3D polyline.
*/
float vtHeightField3d::LineOnSurface(const DLine2 &line, float fSpacing, float fOffset,
bool bInterp, bool bCurve, bool bTrue, FLine3 &output)
{
uint i, j;
FPoint3 v1, v2, v;
float fTotalLength = 0.0f;
int iVerts = 0;
uint points = line.GetSize();
if (bCurve)
{
DPoint2 p2, last(1E9,1E9);
DPoint3 p3;
int spline_points = 0;
CubicSpline spline;
for (i = 0; i < points; i++)
{
p2 = line[i];
if (i > 1 && p2 == last)
continue;
p3.Set(p2.x, p2.y, 0);
spline.AddPoint(p3);
spline_points++;
last = p2;
}
spline.Generate();
// Estimate how many steps to subdivide this line into
const double dLinearLength = line.Length();
float fLinearLength, dummy;
m_LocalCS.VectorEarthToLocal(DPoint2(dLinearLength, 0.0), fLinearLength, dummy);
double full = (double) (spline_points-1);
int iSteps = (uint) (fLinearLength / fSpacing);
if (iSteps < 3)
iSteps = 3;
double dStep = full / iSteps;
FPoint3 last_v;
for (double f = 0; f <= full; f += dStep)
{
spline.Interpolate(f, &p3);
m_LocalCS.EarthToLocal(p3.x, p3.y, v.x, v.z);
FindAltitudeAtPoint(v, v.y, bTrue);
v.y += fOffset;
output.Append(v);
iVerts++;
// keep a running total of approximate ground length
if (f > 0)
fTotalLength += (v - last_v).Length();
last_v = v;
}
}
else
{
// not curved: straight line in earth coordinates
FPoint3 last_v;
for (i = 0; i < points; i++)
{
if (bInterp)
{
v1 = v2;
m_LocalCS.EarthToLocal(line[i].x, line[i].y, v2.x, v2.z);
if (i == 0)
continue;
// estimate how many steps to subdivide this segment into
FPoint3 diff = v2 - v1;
float fLen = diff.Length();
uint iSteps = (uint) (fLen / fSpacing);
if (iSteps < 1) iSteps = 1;
for (j = (i == 1 ? 0:1); j <= iSteps; j++)
{
// simple linear interpolation of the ground coordinate
v.Set(v1.x + diff.x / iSteps * j, 0.0f, v1.z + diff.z / iSteps * j);
FindAltitudeAtPoint(v, v.y, bTrue);
v.y += fOffset;
output.Append(v);
iVerts++;
// keep a running total of approximate ground length
if (j > 0)
fTotalLength += (v - last_v).Length();
last_v = v;
}
}
else
{
m_LocalCS.EarthToLocal(line[i], v.x, v.z);
FindAltitudeAtPoint(v, v.y, bTrue);
v.y += fOffset;
output.Append(v);
}
}
}
return fTotalLength;
}
