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avoid introducing subpixel shift when upscaling using gdal

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This commit is contained in:
Marcin Rudowski 2010-03-17 08:34:43 +00:00
parent 6476c3b850
commit d9d5521a81
1 changed files with 11 additions and 4 deletions
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15
plugins/input/gdal/gdal_featureset.cpp
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@ -108,11 +108,18 @@ feature_ptr gdal_featureset::get_feature(mapnik::query const& q)
box2d<double> intersect = raster_extent.intersect(q.get_bbox()); box2d<double> intersect = raster_extent.intersect(q.get_bbox());
box2d<double> box = t.forward(intersect); box2d<double> box = t.forward(intersect);
//size of resized output pixel in source image domain
double margin_x = 1.0/(fabs(dx)*q.resolution());
double margin_y = 1.0/(fabs(dy)*q.resolution());
if (margin_x < 1)
margin_x = 1.0;
if (margin_y < 1)
margin_y = 1.0;
//select minimum raster containing whole box //select minimum raster containing whole box
int x_off = static_cast<int>(floor(box.minx())); int x_off = rint(box.minx() - margin_x);
int y_off = static_cast<int>(floor(box.miny())); int y_off = rint(box.miny() - margin_y);
int end_x = static_cast<int>(ceil(box.maxx())); int end_x = rint(box.maxx() + margin_x);
int end_y = static_cast<int>(ceil(box.maxy())); int end_y = rint(box.maxy() + margin_y);
//clip to available data //clip to available data
if (x_off < 0) if (x_off < 0)
x_off = 0; x_off = 0;