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Only detect exact collinear intersections in traces #6980

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Merged
grzesiek2010 merged 5 commits into from
Dec 3, 2025
Merged

Only detect exact collinear intersections in traces #6980

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2928232
Allow passing epsilon in intersection detection
seadowg Dec 1, 2025
5e39d4b
Improve adding random intersection to avoid flakey reversed lines
seadowg Dec 1, 2025
e6474c0
Clean up metamorphic test with helpers
seadowg Dec 1, 2025
472058e
Make closed traces intersecting as well
seadowg Dec 2, 2025
74a6464
Add docs for Trace.addRandomIntersectingSegment
seadowg Dec 2, 2025
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Add docs for Trace.addRandomIntersectingSegment
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@seadowg
seadowg committed Dec 2, 2025
commit 74a6464d7f69bdbcd62f1f981d1a059323fae7d0
8 changes: 8 additions & 0 deletions shared/src/test/java/org/odk/collect/shared/geometry/support/GeometryTestUtils.kt
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Expand Up @@ -4,6 +4,7 @@ import org.odk.collect.shared.geometry.LineSegment
import org.odk.collect.shared.geometry.Point
import org.odk.collect.shared.geometry.Trace
import org.odk.collect.shared.geometry.segments
import org.odk.collect.shared.geometry.support.GeometryTestUtils.interpolate
import kotlin.random.Random

object GeometryTestUtils {
Expand Down Expand Up @@ -41,6 +42,13 @@ object GeometryTestUtils {
})
}

/**
* Choose random segment, a random (interpolated) point on that segment and then create a new
* trace with an additional point just beyond that to create an intersecting trace.
*
* Never chooses the last segment as a target for intersecting as that can only create a
* collinear intersection which is unlikely to be accurate due to inaccuracies in [interpolate].
*/
fun Trace.addRandomIntersectingSegment(): Trace {
val intersectionSegment = segments().dropLast(1).random()
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@grzesiek2010 grzesiek2010 Dec 2, 2025

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Why do we need to ignore the last segment? As I understand it, it avoids the scenario when the additional segment lies on the last segment but why? This still would be treated as an intersection.

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@seadowg seadowg Dec 2, 2025

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Good question! I'd meant to add a comment when moving this to a method and then forgotten:

/**
* Choose random segment, a random (interpolated) point on that segment and then create a new
* trace with an additional point just beyond that to create an intersecting trace.
*
* Never chooses the last segment as a target for intersecting as that can only create a
* collinear intersection which is unlikely to be accurate due to inaccuracies in [interpolate].
*/

This is basically the "two consecutive segments intersect" special case, and we test this it specifically (Trace#intersects returns true when two segments and they intersect).

val intersectPosition = Random.nextDouble(0.1, 1.0)
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