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| − | =Natural Earth= | + | = Natural Earth = |
| − | Marble currently uses the very old and outdated MWDBII dataset for vector map | + | == Introduction == |
| + | |||
| + | Marble currently uses the very old and outdated MWDBII dataset for its vector base map such as national borders and coastlines and we really need to replace it with more up-to-date data. However, MWDBII has two key advantages, it is very compact in size enabling Marble to ship it by default, and the individual nodes have a zoom level value which speeds up drawing. | ||
| + | |||
| + | The current vector layer also has the disadvantage of not being able to be manipulated either programtiacally or by the user. This prevents it from being used for such things as KGeography or other educational uses where you would want to select and manipulate a geographic entity. | ||
| + | |||
| + | Improving the vector base maps would thus consist of two closely related parts: | ||
| + | * Improving the vector drawing code to allow interaction with the vectors, and improved performance to allow more detailed vectors to be drawn. | ||
| + | * Importing a new base layer dataset. | ||
| + | |||
| + | == Using NaturalEarth == | ||
The [http://www.naturalearthdata.com/ Natural Earth data set] is a "public domain map dataset available at 1:10m, 1:50m, and 1:110 million scales. Featuring tightly integrated vector and raster data, with Natural Earth you can make a variety of visually pleasing, well-crafted maps with cartography or GIS software." This data set seems ideal as a replacement for the MWDBII. | The [http://www.naturalearthdata.com/ Natural Earth data set] is a "public domain map dataset available at 1:10m, 1:50m, and 1:110 million scales. Featuring tightly integrated vector and raster data, with Natural Earth you can make a variety of visually pleasing, well-crafted maps with cartography or GIS software." This data set seems ideal as a replacement for the MWDBII. | ||
| Line 18: | Line 28: | ||
* Different scale datasets do not match so cannot efficiently be used together for zooming | * Different scale datasets do not match so cannot efficiently be used together for zooming | ||
| − | The 1:10m dataset seems ideal as the base map in Marble as it provides a higher level of detail than the current MWDBII. The 1:110m dataset seems ideal for use in a country selector widget in kdelibs. The 1:50m dataset | + | The 1:10m dataset seems ideal as the base map in Marble as it provides a higher level of detail than the current MWDBII. The 1:110m dataset seems ideal for use in a country selector widget in kdelibs. The 1:50m dataset is less detailed than the current MWDBII so may be less useful. |
Using the data in the default shapefile format is not considered desirable however: | Using the data in the default shapefile format is not considered desirable however: | ||
* No shapefile format support in Marble (yet), would have to rely on an external library or write our own | * No shapefile format support in Marble (yet), would have to rely on an external library or write our own | ||
* Space inefficient (14Mb vs 2.6Mb for MWDBII) | * Space inefficient (14Mb vs 2.6Mb for MWDBII) | ||
| − | * No zoom level attribute or any node level attributes | + | * No zoom level attribute or any node level attributes which would slow drawing |
* Vector level attributes are stored in .dbf format which adds complexity to implementing shapefile support | * Vector level attributes are stored in .dbf format which adds complexity to implementing shapefile support | ||
| + | The ideal solution would seem be to convert the Natural Earth data into a more efficient file format and either calculate and store the zoom level attribute in the file or calculate it on file load. The full Natural Earth dataset would be converted, but would only ship the minimal dataset required with Marble (approx 4-5Mb?) with the remainder of the data later being downloaded via GHNS or as a separate package. | ||
| − | + | === Vector Layer Improvements === | |
| + | The main changes required to Marble will be in the vector layer itself, removing the old PNT file vector drawing code and implementing the new dataset using the new GeoData library vector support. | ||
| + | Two main issues will need to be solved here | ||
| + | * if a new file format is needed for efficient storage | ||
| + | * if a zoom level attribute is needed for fast drawing, and if so where and how to implement the attribute | ||
| + | Some possibilities for the file format are: | ||
| + | * Adapt the existing PNT format used for MWDBII to have a higher degree of accuracy and add an attributes table | ||
| + | * Use the existing Marble serial/cache format which will be faster but the size efficiency may not be sufficient | ||
| + | * Use shapefile by implementing a lightweight parser without dbf support but our own simple attribute table. | ||
| + | * Implement full shapefile support including dbf (possibly using libshape) | ||
| − | * | + | The zoom level problem can be solved by either: |
| + | * Calculate a zoom level for each point during the file conversion and save it in the new file format, but this will require more storage space. | ||
| + | * Improve the vector drawing layer to calculate the zoom level on the fly, which would benefit all vector drawing but may be too slow. | ||
| − | + | The Douglas-Peucker algorithm may be able to be used here. | |
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | Peucker | + | |
| − | + | ||
| − | + | ||
Some pros/cons to consider: | Some pros/cons to consider: | ||
| − | + | * The 1:10m country file is 6.55MB and contains 533,202 points = 12.28 | |
| − | The 1:10m country file is 6.55MB and contains 533,202 points = 12.28 | + | |
bytes/point compared to the PNT which is 745KB and contains 127,246 points = | bytes/point compared to the PNT which is 745KB and contains 127,246 points = | ||
5.85 bytes/point, which would suggest the NE data in PNT format would be half | 5.85 bytes/point, which would suggest the NE data in PNT format would be half | ||
| Line 52: | Line 66: | ||
application of Douglas-Peucker. | application of Douglas-Peucker. | ||
| − | The NE shapefiles have been carefully processed so shared borders and | + | * The NE shapefiles have been carefully processed so shared borders and |
overlapping features like rivers match exactly and other such niceties, | overlapping features like rivers match exactly and other such niceties, | ||
applying the Douglas-Peucker algorithm might affect that. | applying the Douglas-Peucker algorithm might affect that. | ||
| − | A | + | * A shapefile parser would allow users/apps to load other shapefiles. |
| − | shapefiles. | + | |
| − | We would have to reconvert and check the data every time there's a new NE | + | * We would have to reconvert and check the data every time there's a new NE |
release which could be a lot of effort, but an automated shp2pnt script could | release which could be a lot of effort, but an automated shp2pnt script could | ||
prove useful to allow apps/users to display their own shapefiles in a simple | prove useful to allow apps/users to display their own shapefiles in a simple | ||
way. | way. | ||
| − | + | * It is unknown if the D-H algorithm can be deployed in a way to mark each point with a detail level rather than just throwing the points away. | |
| − | + | ||
| − | be deployed in a way to mark each point with a detail level rather than just | + | |
| − | throwing the points away. | + | |
| + | ==== Calculating Zoom Level on the fly ==== | ||
Using GeoPainter and GeoDataLineString ("libgeodata"): | Using GeoPainter and GeoDataLineString ("libgeodata"): | ||
| − | * Apply Douglas-Peuker | + | * Apply Douglas-Peuker dynamically in GeoDataLineString class to set Detail Level |
* When GeoDataLineString modified (add/del point) set dirty flag | * When GeoDataLineString modified (add/del point) set dirty flag | ||
* When node accessed for drawing, Dirty flag would trigger D-P to calculate detail level and unset dirty flag | * When node accessed for drawing, Dirty flag would trigger D-P to calculate detail level and unset dirty flag | ||
* Would benefit all vector formats, e.g. kml, ppx, shp | * Would benefit all vector formats, e.g. kml, ppx, shp | ||
| − | + | ==== Possible new file format (Proposed by John) ==== | |
Potential new Marble file format based on PNT: | Potential new Marble file format based on PNT: | ||
* 1st integer (32 bit): Latitude in arcseconds highest bit indicates new polygon starts: header information has to be read from 3rd integer | * 1st integer (32 bit): Latitude in arcseconds highest bit indicates new polygon starts: header information has to be read from 3rd integer | ||
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* Roughly 533,202 x 8 bytes = 4 Mb for the country borders alone, not including internal border and coastline files | * Roughly 533,202 x 8 bytes = 4 Mb for the country borders alone, not including internal border and coastline files | ||
* If that's too much to ship, then ship the 1:50m dataset as the default and download the 1:10m dataset once online | * If that's too much to ship, then ship the 1:50m dataset as the default and download the 1:10m dataset once online | ||
| + | |||
| + | ==== Possible more size efficient new file format (Proposed by Torsten) ==== | ||
| + | |||
| + | For the Natural Earth Layer providing the Default data set at 0.5 arcminute resolution should be enough. | ||
| + | This fileformat allows for even better packed data than the PNT format. For detailed polygons at arcminute scale on average it should use only 33% of the amount used by PNT. | ||
| + | |||
| + | =====Description of the file format===== | ||
| + | |||
| + | In the fileformat initally a file header is provided that provides the file format version and the number of polygons stored inside the file. A Polygon starts with the Polygon Header which provides the feature id and the number of so called "absolute nodes" that are about to follow. Absolute nodes always contain absolute geodetic coordinates. The Polygon Header also provides a flag that allows to specify whether the polygon is supposed to represent a line string ("0") or a linear ring ("1"). | ||
| + | Each absolute node can be followed by relative nodes: These relative nodes are always nodes that follow in correct order inside the polygon after "their" absolute node. | ||
| + | Each absolute node specifies the number of relative nodes which contain relative coordinates in reference to their absolute node. So an absolute node provides the absolute reference for relative nodes across a theoretical area of 2x2 squaredegree-area (which in practice frequently might rather amount to 1x1 square degrees). | ||
| + | |||
| + | So much of the compression works by just referencing lat/lon diffs to special "absolute nodes". Hence the compression will especially work well for polygons with many nodes with a high node density. | ||
| + | |||
| + | The parser has to convert these relative coordinates to absolute coordinates. | ||
| + | |||
| + | =====File Structure===== | ||
| + | |||
| + | '''File header''' | ||
| + | |||
| + | * quint8: File format version | ||
| + | * quint32: Number of polygons contained in the file. | ||
| + | |||
| + | '''Polygon Header''' | ||
| + | |||
| + | * quint32: Feature id (either Natural Earth or Geonames). | ||
| + | * quint32: Number of parent node chunks to follow | ||
| + | * quint8: Flags: 1st bit: polygonIsClosed | ||
| + | |||
| + | '''Absolute node chunk''' | ||
| + | |||
| + | * qint16: Latitude in halfarcminutes (allowed range = [-10800;+10800 ] halfarcminutes = [-90;+90 ] degrees ) | ||
| + | * qint16: Longitude in halfarcminutes (allowed range = [-21600;+21600 ] halfarcminutes = [-180;+180 ] degrees ) | ||
| + | * qint16: Number of child node chunks to follow (equals "0" if there are no child nodes) | ||
| + | |||
| + | '''Relative node chunk''' | ||
| + | |||
| + | * qint8: Latitude-diff in halfarcminutes compared to the parent (allowed range = [-60;+60] arcminutes = [-1;+1] degrees) | ||
| + | * qint8: Longitude-diff in halfarcminutes compared to the parent (allowed range = [-60;+60] arcminutes = [-1;+1] degrees) | ||
| + | |||
| + | ==== Attribute Database ==== | ||
Metadata file: | Metadata file: | ||
* convert / filter dbf into our own format | * convert / filter dbf into our own format | ||
| + | * could just be csv or xml? or sqlite? | ||
| + | |||
Rather than the Geonames ID, we could just use the Natural Earth object ID, | Rather than the Geonames ID, we could just use the Natural Earth object ID, | ||
then a look-up file/table that matches the NE ID to the ISO / FIPS / whatever | then a look-up file/table that matches the NE ID to the ISO / FIPS / whatever | ||
code (NE provides this in the metadata) and Geonames ID (which we would have | code (NE provides this in the metadata) and Geonames ID (which we would have | ||
to provide). This would allow look-ups via whatever code or ID is available, | to provide). This would allow look-ups via whatever code or ID is available, | ||
| − | and we wouldn't be reliant on Geonames IDs staying constant. | + | and we wouldn't be reliant on Geonames IDs staying constant or being online. |
| − | + | ==== Spatialite ==== | |
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | One option would be to integrate Spatialite and use this as both the data storage for the vectors and as the attribute database. Spatialite is an extension to SQLite implementing a Spatial SQL database. Among the feature this provides is a compact data storage format and the ability to import Shapefiles and CSV files, as well as access all the standard GEOS tools if installed. | |
| + | There is a 20Mb zip file available for Natural Earth in Spatialite format, it is unclear how much of Natural Earth is contained in this. A minimal dataset could be shipped by default with the full dataset downloaded later. | ||
| − | + | Spatial SQL queries could return just those vectors currently in the viewport, but repeated reloading and redrawing could be inefficient. However this may also solve the Level-of-Detail problem. | |
| − | + | ||
| + | The major downside is the dependencies which include SQLite, PROJ and GEOS so on a platform like Windows would require a larger monolithic binary which defeats the purpose of shipping slimmed down data. | ||
| − | + | More research is required here. It may not be a suitable option for the default Atlas view, but would be a very powerful extension for Marble to provide lightweight GIS-like functionality. | |
| − | + | ||
| − | + | === Action Plan === | |
| − | + | ||
| + | A possible action plan is | ||
| + | # Fix GeoPainter LinearRings which contain a pole not rendered correctly | ||
| + | # Implement Douglas-Peucker reduction in GeoDataLineString | ||
| + | # New PNT file format definition (with a different name, MBL?) | ||
| + | # Metadata file format definition | ||
| + | # New GeoData PNT2 file loading code (convert old data). | ||
| + | # shp2pnt2 script to convert shp to new formats (using Perl::shp? there's shp2xxx scripts out there we could copy?), including matching to Geonames ID | ||
| + | # split files into 'ship with', 'download asap', 'ghns' | ||
| + | |||
| + | Later add simple shapefile loading to GeoData, maybe with attibute layer? | ||
| + | |||
| + | == Natural Earth Datasets == | ||
| + | |||
| + | === Dataset Sizes === | ||
| + | |||
| + | Key Natural Earth data files from v1.2, recent updates to 1.3 not included. | ||
| + | <pre> | ||
| + | 1:110m 1:50m 1:10m | ||
| + | ------ ------- ------- | ||
Admin level 0 countries 172 KB 1.36 MB 6.55 MB | Admin level 0 countries 172 KB 1.36 MB 6.55 MB | ||
Admin level 0 land borders 39 KB 301 KB 896 KB | Admin level 0 land borders 39 KB 301 KB 896 KB | ||
| Line 150: | Line 212: | ||
</pre> | </pre> | ||
| − | + | === Dataset Details === | |
* Countries | * Countries | ||
Contents |
Marble currently uses the very old and outdated MWDBII dataset for its vector base map such as national borders and coastlines and we really need to replace it with more up-to-date data. However, MWDBII has two key advantages, it is very compact in size enabling Marble to ship it by default, and the individual nodes have a zoom level value which speeds up drawing.
The current vector layer also has the disadvantage of not being able to be manipulated either programtiacally or by the user. This prevents it from being used for such things as KGeography or other educational uses where you would want to select and manipulate a geographic entity.
Improving the vector base maps would thus consist of two closely related parts:
The Natural Earth data set is a "public domain map dataset available at 1:10m, 1:50m, and 1:110 million scales. Featuring tightly integrated vector and raster data, with Natural Earth you can make a variety of visually pleasing, well-crafted maps with cartography or GIS software." This data set seems ideal as a replacement for the MWDBII.
Advantages:
Disadvantages:
The 1:10m dataset seems ideal as the base map in Marble as it provides a higher level of detail than the current MWDBII. The 1:110m dataset seems ideal for use in a country selector widget in kdelibs. The 1:50m dataset is less detailed than the current MWDBII so may be less useful.
Using the data in the default shapefile format is not considered desirable however:
The ideal solution would seem be to convert the Natural Earth data into a more efficient file format and either calculate and store the zoom level attribute in the file or calculate it on file load. The full Natural Earth dataset would be converted, but would only ship the minimal dataset required with Marble (approx 4-5Mb?) with the remainder of the data later being downloaded via GHNS or as a separate package.
The main changes required to Marble will be in the vector layer itself, removing the old PNT file vector drawing code and implementing the new dataset using the new GeoData library vector support.
Two main issues will need to be solved here
Some possibilities for the file format are:
The zoom level problem can be solved by either:
The Douglas-Peucker algorithm may be able to be used here.
Some pros/cons to consider:
bytes/point compared to the PNT which is 745KB and contains 127,246 points = 5.85 bytes/point, which would suggest the NE data in PNT format would be half the size, so 6 MB in total. This could probably be further reduced by a light application of Douglas-Peucker.
overlapping features like rivers match exactly and other such niceties, applying the Douglas-Peucker algorithm might affect that.
release which could be a lot of effort, but an automated shp2pnt script could prove useful to allow apps/users to display their own shapefiles in a simple way.
Using GeoPainter and GeoDataLineString ("libgeodata"):
Potential new Marble file format based on PNT:
Applying this to the 1:10m dataset:
For the Natural Earth Layer providing the Default data set at 0.5 arcminute resolution should be enough. This fileformat allows for even better packed data than the PNT format. For detailed polygons at arcminute scale on average it should use only 33% of the amount used by PNT.
In the fileformat initally a file header is provided that provides the file format version and the number of polygons stored inside the file. A Polygon starts with the Polygon Header which provides the feature id and the number of so called "absolute nodes" that are about to follow. Absolute nodes always contain absolute geodetic coordinates. The Polygon Header also provides a flag that allows to specify whether the polygon is supposed to represent a line string ("0") or a linear ring ("1"). Each absolute node can be followed by relative nodes: These relative nodes are always nodes that follow in correct order inside the polygon after "their" absolute node. Each absolute node specifies the number of relative nodes which contain relative coordinates in reference to their absolute node. So an absolute node provides the absolute reference for relative nodes across a theoretical area of 2x2 squaredegree-area (which in practice frequently might rather amount to 1x1 square degrees).
So much of the compression works by just referencing lat/lon diffs to special "absolute nodes". Hence the compression will especially work well for polygons with many nodes with a high node density.
The parser has to convert these relative coordinates to absolute coordinates.
File header
Polygon Header
Absolute node chunk
Relative node chunk
Metadata file:
Rather than the Geonames ID, we could just use the Natural Earth object ID, then a look-up file/table that matches the NE ID to the ISO / FIPS / whatever code (NE provides this in the metadata) and Geonames ID (which we would have to provide). This would allow look-ups via whatever code or ID is available, and we wouldn't be reliant on Geonames IDs staying constant or being online.
One option would be to integrate Spatialite and use this as both the data storage for the vectors and as the attribute database. Spatialite is an extension to SQLite implementing a Spatial SQL database. Among the feature this provides is a compact data storage format and the ability to import Shapefiles and CSV files, as well as access all the standard GEOS tools if installed.
There is a 20Mb zip file available for Natural Earth in Spatialite format, it is unclear how much of Natural Earth is contained in this. A minimal dataset could be shipped by default with the full dataset downloaded later.
Spatial SQL queries could return just those vectors currently in the viewport, but repeated reloading and redrawing could be inefficient. However this may also solve the Level-of-Detail problem.
The major downside is the dependencies which include SQLite, PROJ and GEOS so on a platform like Windows would require a larger monolithic binary which defeats the purpose of shipping slimmed down data.
More research is required here. It may not be a suitable option for the default Atlas view, but would be a very powerful extension for Marble to provide lightweight GIS-like functionality.
A possible action plan is
Later add simple shapefile loading to GeoData, maybe with attibute layer?
Key Natural Earth data files from v1.2, recent updates to 1.3 not included.
KDE TechBase
1:110m 1:50m 1:10m
------ ------- -------
Admin level 0 countries 172 KB 1.36 MB 6.55 MB
Admin level 0 land borders 39 KB 301 KB 896 KB
Admin level 0 sea borders 12 KB 40 KB 79 KB
Admin level 0 disputed 40 KB 157 KB
Admin level 1 regions 39 KB 339 MB 13.9 MB *
Admin level 1 land borders 16 KB 60 KB 4.82 MB
Coastlines 79 KB 883 KB 2.15 MB
Rivers 19 KB 420 KB 3.29 MB
Lakes 10 KB 286 KB 786 MB
Glaciers 13 KB 208 KB 1.23 MB
Dateline 18 KB 18 KB 18 KB
Playas 18 KB 106 KB
Ice Shelves 105 KB 211 KB
Minor Islands 449 KB
Reefs 171 KB
------- ------- ---------
417 KB 4.08 MB 34.03 MB
* level 1 regions are USA/Canada only at 110m and 50m, but whole world at 10m,
perfect for KGeography use :-)
Other useful files:
Physical Features Land 146 KB 1.50 MB 692 KB
Physical Features Sea 348 KB 836 KB 836 MB
Populated Places 347 KB 1.48 MB
Urban Areas 439 KB 3.48 MB
Bathmetry 11.64 MB
sovereign states. Includes dependencies (French Polynesia), map units (U.S. Pacific Island Territories) and sub-national map subunits (Corsica versus mainland Metropolitan France).
