Cannot read context in shapefile with mapnik

[Wingong]

Cannot read context in shapefile with mapnik

[artemp]

@Wingong - I'm assuming you're trying to access Feature attributes. If so, you can use feature_kv_iterator

#include <mapnik/feature_kv_iterator.hpp>
.....

while (auto feature = features->next())
{
   feature_kv_iterator itr(*feature, true);
   feature_kv_iterator end(*feature); 
   for (; itr != end; ++itr)
   {
      std::cerr << std::get<0>(*itr) << ":" << std::get<1>(*itr).to_string() << std::endl;
   }
}

or

auto itr = feature->begin();
auto end = feature->end();
for (; itr != end; ++itr) { ... }

or

for (auto const& kv : feature)
{
        std::cerr << std::get<0>(kv) << ":" << std::get<1>(kv).to_string();
}

HTH

[Wingong]

@artemp I tried feature_kv_iterator, but it seems not working. itr is equal to end, so nothing was iterate. Besides, I read the code of the input file shape.input, exactly dbf.hpp and dbf.cpp in it. When reading dBase file, it doesn't load records, but only the header (using read_header() function). I thought if it could cause the problem?

[artemp]

@Wingong Could you share your shapefile if it's not too large?

[Wingong]

@artemp Of course, but i don't know how to upload file - however, it is just the demo shapefile in mapnik source code, like src/demo/data/boundaries and others. Thanks very much!

[Wingong]

@artemp update: using mapnik::rule and add rules to style can filter the write shape (like r.set_filter(parse_expression("[NAME_EN] = 'Ontario'"));). I tried using map.query_point(index, x, y), and features in it contain correct context.