james-willis commented on code in PR #3119:
URL: https://github.com/apache/sedona/pull/3119#discussion_r3632767628
##########
common/src/main/java/org/apache/sedona/common/raster/Rasterization.java:
##########
@@ -200,58 +200,74 @@ private static void rasterizeLineString(
double x1 = (end.x - params.upperLeftX) / params.scaleX;
double y1 = (end.y - params.upperLeftY) / params.scaleY;
- // Apply Bresenham for this segment
- drawLineBresenham(params, x0, y0, x1, y1, value, 0.2);
+ traverseSegment(params, x0, y0, x1, y1, value);
}
}
}
- // Modified Bresenham with Fractional Steps
- private static void drawLineBresenham(
- RasterizationParams params,
- double x0,
- double y0,
- double x1,
- double y1,
- double value,
- double stepSize) {
+ /**
+ * Burns every grid cell the segment passes through, in pixel space where
cell (i, j) covers [i, i
+ * + 1) x [j, j + 1). Uses exact cell traversal (Amanatides-Woo): it steps
from one cell-boundary
+ * crossing to the next, so a cell is burned whenever the segment enters it,
however briefly. A
+ * fixed-step sampling walk instead misses cells crossed over a distance
shorter than the step.
+ */
+ private static void traverseSegment(
+ RasterizationParams params, double x0, double y0, double x1, double y1,
double value) {
+
+ int width = params.writableRaster.getWidth();
+ int height = params.writableRaster.getHeight();
double dx = x1 - x0;
double dy = y1 - y0;
- // Compute the number of steps based on the larger of dx or dy
- double distance = Math.sqrt(dx * dx + dy * dy);
- int steps = (int) Math.ceil(distance / stepSize);
-
- // Calculate the step increment for each axis
- double stepX = dx / steps;
- double stepY = dy / steps;
-
- // Start stepping through the line
- double x = x0;
- double y = y0;
-
- for (int i = 0; i <= steps; i++) {
- int rasterX = (int) (Math.floor(x));
- int rasterY = (int) (Math.floor(y));
-
- // Adjust for bottom-up rasters
- // Reverse the y index
- if (params.bottomUp) {
- rasterY = params.writableRaster.getHeight() - 1 - rasterY;
+ int stepX = (int) Math.signum(dx);
+ int stepY = (int) Math.signum(dy);
+
+ int x = (int) Math.floor(x0);
+ int y = (int) Math.floor(y0);
+ int endX = (int) Math.floor(x1);
+ int endY = (int) Math.floor(y1);
+
+ // Parametric t (point = p0 + t * (p1 - p0)) at the first grid line
crossed on each axis, and
+ // the t spanned by one full cell. Infinity where the segment does not
move along that axis.
+ double tDeltaX = dx != 0 ? Math.abs(1.0 / dx) : Double.POSITIVE_INFINITY;
+ double tDeltaY = dy != 0 ? Math.abs(1.0 / dy) : Double.POSITIVE_INFINITY;
+ double tMaxX = dx > 0 ? (x + 1 - x0) / dx : (dx < 0 ? (x - x0) / dx :
Double.POSITIVE_INFINITY);
+ double tMaxY = dy > 0 ? (y + 1 - y0) / dy : (dy < 0 ? (y - y0) / dy :
Double.POSITIVE_INFINITY);
+
+ // The endpoints are clipped to the geometry extent, so the walk covers at
most the grid's
+ // width + height cells; the bound also guards against a floating-point
overshoot never reaching
+ // the end cell.
+ int maxSteps = width + height + 2;
+ for (int i = 0; i <= maxSteps; i++) {
+ burnCell(params, x, y, value, width, height);
+ if (x == endX && y == endY) {
+ break;
}
-
- // Only write if within raster bounds
- if (rasterX >= 0
- && rasterX < params.writableRaster.getWidth()
- && rasterY >= 0
- && rasterY < params.writableRaster.getHeight()) {
- params.writableRaster.setSample(rasterX, rasterY, 0, value);
+ // On an exact corner crossing (segment passes through a lattice point)
step both axes at
+ // once, so only the two cells the segment actually passes through are
burned rather than the
+ // off-diagonal pair as well.
+ if (tMaxX < tMaxY) {
Review Comment:
good call. I computed each crossing without the accumulation to avoid the
ULP rounding drift.
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: [email protected]
For queries about this service, please contact Infrastructure at:
[email protected]
