Add Header Only API for Linestring-Polygon Distance

cpp/include/cuspatial/experimental/detail/functors.cuh

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+/*
+ * Copyright (c) 2023, NVIDIA CORPORATION.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <cuspatial/cuda_utils.hpp>
+#include <cuspatial/experimental/geometry/segment.cuh>
+#include <cuspatial/traits.hpp>
+
+#include <thrust/binary_search.h>
+
+namespace cuspatial {
+namespace detail {
+
+/**
+ * @brief Given iterator a pair of offsets, return the number of elements between the offsets.
+ *
+ * Example:
+ * pair of offsets: (0, 3), (3, 5), (5, 8)
+ * number of elements between offsets: 3, 2, 3
+ *
+ * @tparam OffsetPairIterator Must be iterator type to thrust::pair of indices.
+ * @param p Iterator of thrust::pair of indices.
+ */
+struct offset_pair_to_count_functor {
+  template <typename OffsetPairIterator>
+  CUSPATIAL_HOST_DEVICE auto operator()(OffsetPairIterator p)
+  {
+    return thrust::get<1>(p) - thrust::get<0>(p);
+  }
+};
+
+/**
+ * @brief Convert counts of points to counts of segments in a linestring.
+ *
+ * A Multilinestring is composed of a series of Linestrings. Each Linestring is composed of a
+ * segments. The number of segments in a multilinestring is the number of points in the
+ * multilinestring subtracting the number of linestrings.
+ *
+ * Caveats: This has a strong assumption that the Multilinestring does not contain empty linestring.
+ * While each non-empty linestring in the multilinestring can cause 1 invalid segment, an empty
+ * multilinestring not introduce and invalid segments since it does not contain any points.
+ *
+ * @tparam IndexPair Must be iterator to a pair of counts
+ * @param n_point_linestring_pair A pair of counts, the first is the number of points, the second is
+ * the number of linestrings.
+ */
+struct point_count_to_segment_count_functor {
+  template <typename IndexPair>
+  CUSPATIAL_HOST_DEVICE auto operator()(IndexPair n_point_linestring_pair)
+  {
+    auto nPoints      = thrust::get<0>(n_point_linestring_pair);
+    auto nLinestrings = thrust::get<1>(n_point_linestring_pair);
+    return nPoints - nLinestrings;
+  }
+};
+
+/**
+ * @brief Given an iterator of offsets, return an iterator of offsets subtracted by the index.
+ *
+ * @tparam OffsetIterator Iterator type to the offset
+ *
+ * Caveats: This has a strong assumption that the Multilinestring does not contain empty linestring.
+ * While each non-empty linestring in the multilinestring can cause 1 invalid segment, an empty
+ * multilinestring not introduce and invalid segments since it does not contain any points.
+ */
+template <typename OffsetIterator>
+struct to_subtracted_by_index_iterator {
+  OffsetIterator begin;
+
+  template <typename IndexType>
+  CUSPATIAL_HOST_DEVICE auto operator()(IndexType i)
+  {
+    return begin[i] - i;
+  }
+};
+
+/// Deduction guide for to_subtracted_by_index_iterator
+template <typename OffsetIterator>
+to_subtracted_by_index_iterator(OffsetIterator) -> to_subtracted_by_index_iterator<OffsetIterator>;
+
+/**
+ * @brief Return a segment from the a partitioned range of points
+ *
+ * Used in a counting transform iterator. Given an index of the segment, offset it by the number of
+ * skipped segments preceding i in the partitioned range of points. Dereference the corresponding
+ * point and the point following to make a segment.
+ *
+ * @tparam OffsetIterator the iterator type indicating partitions of the point range.
+ * @tparam CoordinateIterator the iterator type to the point range.
+ */
+template <typename OffsetIterator, typename CoordinateIterator>
+struct to_valid_segment_functor {
+  using element_t = iterator_vec_base_type<CoordinateIterator>;
+
+  OffsetIterator begin;
+  OffsetIterator end;
+  CoordinateIterator point_begin;
+
+  template <typename IndexType>
+  CUSPATIAL_HOST_DEVICE segment<element_t> operator()(IndexType i)
+  {
+    auto kit = thrust::upper_bound(thrust::seq, begin, end, i);
+    auto k   = thrust::distance(begin, kit);
+    auto pid = i + k - 1;
+
+    return segment<element_t>{point_begin[pid], point_begin[pid + 1]};
+  }
+};
+
+/// Deduction guide for to_valid_segment_functor
+template <typename OffsetIterator, typename CoordinateIterator>
+to_valid_segment_functor(OffsetIterator, OffsetIterator, CoordinateIterator)
+  -> to_valid_segment_functor<OffsetIterator, CoordinateIterator>;
+
+}  // namespace detail
+}  // namespace cuspatial