FGFS-4.1/simgear
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Revise SGBucket::get_width_m

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- remove the 0.5 degree offset away from the equator, which was
  causing wrap-around at the poles
- add a new helper to get the highest latitude of a tile (which may
  be +/- 90 for the polar cap tiles), and use this to compute radius
- special case the polar-caps and return a fixed, small width so
  the tile-manager loads all tiles.
This commit is contained in:
James Turner 2014-02-13 18:49:16 +00:00
parent 6b9ce935cd
commit 00d8849a28
3 changed files with 36 additions and 9 deletions
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33
simgear/bucket/newbucket.cxx
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@ -236,17 +236,32 @@ double SGBucket::get_height() const {
return SG_BUCKET_SPAN;
}
// return width of the tile in meters
double SGBucket::get_width_m() const {
double clat = (int)get_center_lat();
if ( clat > 0 ) {
clat = (int)clat + 0.5;
} else {
clat = (int)clat - 0.5;
double SGBucket::get_highest_lat() const
{
unsigned char adjustedY = y;
if (lat >= 0) {
// tile is north of the equator, so we want the top edge. Add one
// to y to achieve this.
++adjustedY;
}
double clat_rad = clat * SGD_DEGREES_TO_RADIANS;
return lat + (adjustedY / 8.0);
}
// return width of the tile in meters. This function is used by the
// tile-manager to estimate how many tiles are in the view distance, so
// we care about the smallest width, which occurs at the highest latitude.
double SGBucket::get_width_m() const
{
double clat_rad = get_highest_lat() * SGD_DEGREES_TO_RADIANS;
double cos_lat = cos( clat_rad );
if (fabs(cos_lat) < SG_EPSILON) {
// happens for polar tiles, since we pass in a latitude of 90
// return an arbitrary small value so all tiles are loaded
return 10.0;
}
double local_radius = cos_lat * SG_EQUATORIAL_RADIUS_M;
double local_perimeter = local_radius * SGD_2PI;
double degree_width = local_perimeter / 360.0;

7
simgear/bucket/newbucket.hxx
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@ -206,6 +206,13 @@ public:
return lat + y / 8.0 + SG_HALF_BUCKET_SPAN;
}
/**
* @return the highest (furthest from the equator) latitude of this
* tile. This is the top edge for tiles north of the equator, and
* the bottom edge for tiles south
*/
double get_highest_lat() const;
/**
* @return the width of the tile in degrees.
*/

5
simgear/bucket/test_bucket.cxx
View File

@ -110,6 +110,9 @@ void testPolar()
COMPARE(b1.get_x(), 0);
COMPARE(b1.get_y(), 7);
COMPARE_EP(b1.get_highest_lat(), 90.0);
COMPARE_EP(b1.get_width_m(), 10.0);
COMPARE(b2.get_chunk_lat(), 89);
COMPARE(b2.get_chunk_lon(), 0);
COMPARE(b2.get_x(), 0);
@ -137,6 +140,8 @@ void testPolar()
COMPARE(b5.get_x(), 0);
COMPARE(b5.get_y(), 0);
COMPARE(b5.gen_index(), b6.gen_index());
COMPARE_EP(b5.get_highest_lat(), -90.0);
COMPARE_EP(b5.get_width_m(), 10.0);
SGGeod actualSouthPole1 = b5.get_corner(0);
SGGeod actualSouthPole2 = b5.get_corner(1);