用protobuf解析MVT矢量瓦片的C++代码

以下是使用protobuf解析MVT矢量瓦片的C代码示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <stdint.h>
#include "vector_tile.pb-c.h"

#define BUFFER_SIZE 4096
#define MAX_FEATURES 100

// Function to read the MVT tile data from a file
int read_tile(const char* filename, uint8_t** buffer, size_t* length) {
  FILE* f = fopen(filename, "rb");
  if (!f) {
    return -1;
  }
  fseek(f, 0, SEEK_END);
  *length = ftell(f);
  fseek(f, 0, SEEK_SET);
  *buffer = (uint8_t*)malloc(*length);
  if (*buffer) {
    fread(*buffer, 1, *length, f);
  }
  fclose(f);
  return 0;
}

// Function to parse the MVT tile data using protobuf-c
void parse_tile(uint8_t* buffer, size_t length) {
  VectorTile__Tile* tile = vector_tile__tile__unpack(NULL, length, buffer);
  if (!tile) {
    printf("Failed to parse MVT tile data.\n");
    return;
  }

  printf("Tile size: %d\n", tile->n_layers);

  for (int i = 0; i < tile->n_layers; i++) {
    printf("Layer %d\n", i);
    VectorTile__Tile__Layer* layer = tile->layers[i];

    printf("Layer name: %s\n", layer->name);
    printf("Extent: %d\n", layer->extent);
    printf("Version: %d\n", layer->version);

    int feature_count = layer->n_features < MAX_FEATURES ? layer->n_features : MAX_FEATURES;
    for (int j = 0; j < feature_count; j++) {
      VectorTile__Tile__Feature* feature = layer->features[j];

      printf("Feature %d\n", j);
      printf("Type: %d\n", feature->type);
      printf("ID: %d\n", feature->id);

      for (int k = 0; k < feature->n_tags; k += 2) {
        int tag_key = feature->tags[k];
        int tag_value = feature->tags[k + 1];
        printf("Tag: %s=%s\n", layer->keys[tag_key], layer->values[tag_value]);
      }

      for (int k = 0; k < feature->n_geometry; k++) {
        VectorTile__Tile__Geometry* geometry = feature->geometry[k];

        for (int l = 0; l < geometry->n_commands; l++) {
          int command = geometry->commands[l];
          int length = command & 0x7;
          int type = command >> 3;

          switch (type) {
            case VECTOR_TILE__TILE__GEOMETRY__COMMAND_TYPE__MOVE_TO:
              printf("Move to (%d, %d)\n", geometry->x[l], geometry->y[l]);
              break;
            case VECTOR_TILE__TILE__GEOMETRY__COMMAND_TYPE__LINE_TO:
              printf("Line to (%d, %d)\n", geometry->x[l], geometry->y[l]);
              break;
            case VECTOR_TILE__TILE__GEOMETRY__COMMAND_TYPE__CLOSE_PATH:
              printf("Close path\n");
              break;
            default:
              printf("Unknown command type %d\n", type);
          }
        }
      }
    }
  }

  vector_tile__tile__free_unpacked(tile, NULL);
}

int main(int argc, char** argv) {
  if (argc != 2) {
    printf("Usage: %s <MVT file>\n", argv[0]);
    return 1;
  }

  uint8_t* buffer;
  size_t length;
  if (read_tile(argv[1], &buffer, &length) != 0) {
    printf("Failed to read MVT tile file.\n");
    return 1;
  }

  parse_tile(buffer, length);

  free(buffer);
  return 0;
}

该代码首先读取MVT矢量瓦片数据，然后使用protobuf-c解析该数据。解析后，该代码会打印出每个图层中包含的要素和几何形状信息。请注意，此代码仅打印每个图层中的前100个要素，以避免输出过多的信息。