当前位置:网站首页>[Mori city] random talk on GIS data (II)
[Mori city] random talk on GIS data (II)
2022-07-07 02:26:00 【51CTO】
In the first chapter “GIS Data rambling ( One )” It briefly introduces GIS The concept of vector data and grid data in data , And common GIS Data file type . In this ramble, we will continue to talk about map services .
Spatial database
GIS The history of development is to follow IT The development history of technology , For example, various vector data mentioned above 、 The files of raster data belong to spatial data . Due to the big data attribute of geographic data , The data volume of an urban geographic information system may reach dozens GB, If we consider the storage of image data , Maybe hundreds GB. Massive data of geographic information system , Bring the system operation 、 Data organization and storage 、 A series of technical difficulties such as network transmission , Naturally, it also increases the difficulty of data management .
in order to Better management GIS data It developed Spatial database , With the development of technology, many mainstream databases basically support spatial data expansion , such as MySQL、Oracle、PostGIS etc. .
Map service
With spatial database management GIS data , How to connect these data ? You can't guide them one by one GeoJSON Well .OGC【 Open Geospatial Information Alliance (Open Geospatial Consortium-OGC)】 Some services are designed for the data source mentioned above, such as WMS、WMTS、WFS wait .
stay GIS Of Web Application , No matter the original data is stored in the file , It's better to store it in the database , These standard map services can be used in the network http(s) Protocol for access sharing . commonly GIS Large factory Server Product or open source GIS Server( such as GeoServer) All support publishing these map services .
WMS(Web Map Service)
The main capability of this service is to GIS data ( Whether the original data is vector data or raster data ) Issued as “ picture ”. That is, according to the client request parameters ( Mainly bbox Range ), The server returns the corresponding “ picture ”.
WMS Three common operations :
• GetMap: According to the request parameters , Return a picture
• GetFeatureinfo: According to the coordinates in the request parameters , Return the queried object attribute information
• GetCapabilities: Return the metadata of the service
take “ Site ”、“ The railway ”、“ lakes ” Data release WMS service , You can use the WMS Service basis bbox Range request corresponding data rendered map image . Most map application front-end library pairs WMS Services are supported by corresponding layers .
WMS Sometimes called “ dynamic ” Map service , The server will send the requested parameters from the client ( Such as layer name 、BBox Within the scope of ) Go to the database or file to search and query the data in the corresponding range , Then render the image according to the configured style , Finally back to the client .
If the client requests frequently or the concurrent requests are high , The map layer contains a huge amount of data 、 When the configured style is complex , The load borne by the server will increase . therefore , Later, a map tile caching mechanism was developed . To put it simply, we should follow certain rules “ Rendering ” The map image after is stored on the server , When the client calls again, the server will directly return “ cache ” Pictures of the , No need to... Again “ dynamic ” Rendering , So there it is Map tiles service .
Map tile service
Map tiles It refers to the map within a certain range according to a certain size and format , By zoom level or scale bar , A square grid picture cut into rows and columns , The sliced square grid image is called tiles (tile).
Tile Map pyramid model is a multi-resolution hierarchical model , From the bottom of the tile pyramid to the top , Resolution is getting lower , But the geographical scope of the representation remains the same .
Google The map uses Web Mecator Projection and tile grading cutting scheme , It has also become the de facto standard of Internet maps .
WMTS(Web Map Tile Service)
WMTS It's a kind of OGC Defined map tile service standard ,WMTS yes OGC The proposed cache technology standard , That is to say, the map that is cut into tiles of a certain size is cached on the server side , Only these pre-defined single tile services are provided to clients , Put more data processing operations such as layer overlay on the client , So as to alleviate GIS The pressure of server-side data processing .
There is also Google Tile、 OSGeo Of TMS(Tile Map Service) wait , Although different specifications , But basically, it can be in uearth API Try to use TileLayer Load these map tile Services .
How to use this data in low code loading ? The lake can be 、 Railway and other data utilization GeoServer Published as WMTS and TMS Map service , In low code ThingJS Online development and utilization uearth API Of TileLayer Loading .
Whether it's WMS Service or map tile ( section ) service , The final call is “ picture ” Not the data itself . Although the browser has little pressure to render , But the style is not flexible , Only in low code ThingJS Adjust the effect of the overall picture , Inconvenient effect adjustment ( If you adjust the map style configuration of the server, you need to slice again ). So there's... Again WFS Service to directly provide the operation of vector data .
WFS(Web Feature Service)
WFS Provides the client with Operate on vector data The ability of , In addition to returning query data , Also provides new 、 modify 、 Standard interface for deleting data . It means that what you see is a vector graph , Not a picture .
The difference between vector graphics and picture elements is that they will not be distorted with the change of magnification , Vector elements facilitate interaction and editing 、 Modify the shape, etc .
How to use this data in low code loading ?
utilize GeoServer Put the data ( Like a railway ) Issued as WFS The service queries directly on the front end , After returning the result ( It's usually geojson Format ), use ThingJS/uearth relevant API Drawing .
Tool recommendation
Mori City : One click generation 3D City , Built in multiple templates , Free editing
• Mori city currently provides nationwide 110 Multiple cities Standard 3D scene construction service , Make the construction speed of urban 3D scene increase to minute level .
• Sen city supports the insertion and automatic fusion of different types of city data , And provide friendly and powerful scene editing ability and performance processing ability , Not required GIS、 Modeling and other professional skills , It's easy DIY Own cool 3D city scene .
• Mori city has open City scene output capability , There is no need to worry about the compatibility of subsequent use of the scene .
Low code ThingJS: Low code and flexible development of digital twin visualization applications
• Low code ThingJS Provides rich 3D Development API、 Perfect development documents and video tutorials , Familiar with basic JavaScript Front end knowledge can be used to develop digital twin visualization application .
• Low code ThingJS Is pure H5 Of WebGL framework , Can be found in Run freely in all kinds of mainstream web browsers , Including direct access and operation at the mobile terminal .
• Low code ThingJS Provide full lifecycle development components , Greatly improve the development efficiency of digital twin visualization project .
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