Bounding box hit rate for file nodes.dat is only 0% (1/116) What can I do to remov

H <a class="user-mention notranslate" data-hovercard-type="user" data-hovercard-url="/

Bounding box and Speed about libosmscout HOT 2 OPEN

DerKleinePunk commented on June 3, 2024

Bounding box and Speed

from libosmscout.

Comments (2)

Framstag commented on June 3, 2024

H @DerKleinePunk. I was in holiday, so sorry for the late answer.

The warning comes from DataFIle.h.

  bool DataFile<N>::GetByOffset(IteratorIn begin, IteratorIn end,
                                size_t size,
                                const GeoBox& boundingBox,
                                std::vector<ValueType>& data) const

it is called by

  bool Database::GetNodesByOffset(const std::vector<FileOffset>& offsets,
                                  const GeoBox& boundingBox,
                                  std::vector<NodeRef>& nodes) const

which again it is called by

  bool MapService::GetNodes(const AreaSearchParameter& parameter,
                            const TypeInfoSet& nodeTypes,
                            const GeoBox& boundingBox,
                            bool prefill,
                            const TileRef& tile) const

The method gets a number of file offset from the index together with a bounding box (which is likely the visible map area). The warning means that most of the offsets returned by the index are actually not in the given area. This means that the index is too unspecific. It finds objects that are later on filtered out. This may be a performance penalty if IO is slow and CPU is fast. It is a hint that for this special area, the index should have possibly been generated with other parameters. If the warning comes only sporadically I would ignore it, if it often happens you can play with the parameters, but you have to measure if the new parameters are actually better (e.g. index with different parameters might require more memory or more IO during index lookup).

The AreaNodeIndex Generator has the following parameters:

  MagnificationLevel           areaNodeGridMag;          //<! Magnification level for the index grid
  uint16_t                     areaNodeSimpleListLimit;  //<! If a type has less entries, we just store them plain
  uint16_t                     areaNodeTileListLimit;    //<! If a type has less entries in a tile, we store it as list
  uint16_t                     areaNodeTileListCoordLimit;//<! If a type has less entries we store the coord in tile lists
  MagnificationLevel           areaNodeBitmapMaxMag;      //<! Maximum Magnification level for bitmap index
  uint16_t                     areaNodeBitmapLimit;       //<! All cells must have less entries for a given zoom level

with the following default values:

      areaNodeGridMag(14),
      areaNodeSimpleListLimit(500),
      areaNodeTileListLimit(100),
      areaNodeTileListCoordLimit(1000),
      areaNodeBitmapMaxMag(20),
      areaNodeBitmapLimit(20),

I would either start with increasing the GridMag to 15 or decrease the list limits by factor 2? I assume that the index file size will increase.

The Import application should have command line options for these. If one is missing that add it yourself or tell us (or change default value in your code). You have to regenerate the index after changing values.

from libosmscout.

DerKleinePunk commented on June 3, 2024

I hope you Holiday are good.
Thanks I will Test it and Report.

from libosmscout.

Bounding box and Speed about libosmscout HOT 2 OPEN

Comments (2)

Related Issues (20)

Recommend Projects

React

Vue.js

Typescript

TensorFlow

Django

Laravel

D3

Recommend Topics

javascript

web

server

Machine learning

Visualization

Game

Recommend Org

Facebook

Microsoft

Google

Alibaba

D3

Tencent