Technical Report. SimpleFeatureService. Ing. Andrea Aime Ing. Simone Giannecchini GeoSolutions S.A.S. Date 10/11/2010 Version 0.1

Transcription

1 2010 Technical Reprt SimpleFeatureService Ing. Andrea Aime Ing. Simne Giannecchini. Date 10/11/2010 Versin 0.1

2 Cntents Recrd f Changes... 4 SimpleFeatureService prtcl v Supprted URLs... 5 Capabilities dcument... 5 Layer descriptin dcument... 7 Layer querying... 9 Mapping the prtcl nt the GeTls datastre API Page 2 f 12

3 N table f figures entries fund. Page 3 f 12

4 Recrd f Changes Versin When Wh What /11/201 AAime First Versin Page 4 f 12

5 SimpleFeatureService prtcl The OpenDataStre prtcl is a simplified feature prtcl using GeJSON as the encding frmat lsely based n RESTful principles (but nt fully cmpliant with them t allw fr better perfrmance and handling f large requests). It is heavily inspired by the MapFish prtcl, but with mdificatins t make it pssible t build an efficient GeTls data stre n tp f it and cpe with mre real wrld use cases. GeTls already prvides an implementatin f a streaming parser/encder as well as a Mapfish prtcl riented (but still incmplete) data stre. Supprted URLs used t prvide a list f available layers returns a descriptin f the feature type used t query the layer features used t grab a specific feature by id Capabilities dcument The capabilities dcument lists the available layers and prvides the basic infrmatin abut the service: name f the layers, their bunding bx and the native SRS. The pattern is as fllws: [ { "name": "layer1", "bbx" : [ -10, -40, 30, 80], "crs" : "urn:gc:def:crs:epsg:4326", Page 5 f 12

6 "axisrder" : yx... }, { "name": "layer2", "bbx" : [ , , , ], "crs" : "urn:gc:def:crs:epsg:32632" }, ] Fllwing the GeJSON specificatin suggestins the crs is expressed in urn frm. If a layer fr any reasn has flipped axis it will indicate s by using the axisrder parameter, if that infrmatin is missing the layer is suppsed t be in x/y, ln/lat rder regardless f the ntatin used t express the crs. Page 6 f 12

7 Layer descriptin dcument The layer descriptin dcument lists the available fields and their type: [ {"name":"string","quantity":"number",...} ] Fr example, the tpp:states GeServer dem layer descriptin wuld lk like: [ {"the_gem":"multiplygn", "STATE_NAME":"string", "STATE_FIPS":"string", "SUB_REGION":"string", "STATE_ABBR":"string", "LAND_KM":"nunumber", "WATER_KM":"number", "PERSONS":"number", "FAMILIES":"number", "HOUSHOLD":"number", "MALE":"number", "FEMALE":"number", "WORKERS":"number", "DRVALONE":"number", "CARPOOL":"number", "PUBTRANS":"number", "EMPLOYED":"number", "UNEMPLOY":"number", "SERVICE":"number", "MANUAL":"number", "P_MALE":"number", "P_FEMALE":"number", "SAMP_POP":"number" } ] GeJSON by default supprts nly the basic gemetry types, strings and numbers. This specificatin supprts: gemetric types: Gemetry, Pint, MultiPint, LineString, MultiLineString, Plygn, MultiPlygn, Gemetry Cllectin field types: string, number, blean, timestamp A number can be expressed in integral r flating pint ntatin. A blean can be true r false A timestamp is expressed as a Unix date (number f secnds since Jan ), see als Page 7 f 12

8 JSON can in thery describe cmplex structures in which an attribute is a cmplex ne cntaining subattributes. This first prtcl specificatin wn t supprt that case. Page 8 f 12

9 Layer querying This fllws clsely the MapFish prtcl, with ne variatin, crs in the place f epsg t be cnsistent with the GeJSON ntatin, a utput mde t supprt cunt and bund peratins, and hints t allw fr implementatin specific parameters t be passed ver: n_gem=true: s that the returned feature has n gemetry ("gemetry": null) attrs={field1}[,{field2},...]: t restrict the list f prperties returned in the feature limit={num}: limit the number f features t num features (maxfeatures is an alias t limit) ffset={num}: skip num features rder_by={field}: rder the features using field dir=desc ASC: determine the rdering directin (applies nly if rder_by is specified) ln={x}: the x crdinate f the center f the search regin, this crd's prjectin system can be specified with the epsg parameter lat={y}: the y crdinate f the center f the search regin, this crd's prjectin system can be specified with the epsg parameter tlerance={num}: the tlerance arund the center f the search regin, expressed in the units f the ln/lat crds' prjectin system bx={xmin,ymin,xmax,ymax}: a list f crdinates representing a bunding bx, the crds' prjectin system can be specified with the epsg parameter gemetry={gejsn}: a GeJSON string representing a gemetry, the crds' prjectin system can be specified with the epsg parameter crs={num}: the EPSG cde f the ln, lat r bx values queryable={field1}[,{field2},...]}: the names f the feature fields that can be queried {field} {query_p}={value}: specify a filter expressin, field must be in the list f fields specified by queryable, supprted query_p's are: Page 9 f 12

10 eq: equal t ne: nt equal t lt: lwer than lte: lwer than r equal t gt: greater than gte: greater than r equal t like ilike mde. Can be features, cunt, bunds. In features mde it just returns the features in jsn frmat, in cunt mde it returns a cunt f the features satisfying the filters, in bunds mde it returns the bunding bx f the features satisfying the filter as a jsn array hints. A map prviding implementatin specific hints. The expected frmat is key1:value1;key2:value2;... As a variant cmpared t the MapFish prtcl the abve can als be emitted as a POST request using the applicatin/x-www-frm-urlencded mime type fr the cntents. This is a departure frm restful principles that allws t send large queries (hints can be big) and keep the implementatin simple. The MapFish prtcl uses POST t create new features, if we re ging t supprt writing in the future we ll make sure the POST request t create/update data is ging t use the applicatin/jsn mime type instead. Page 10 f 12

11 Mapping the prtcl nt the GeTls datastre API The implementatin shuld be based n the GeRest stre. DataStre API Prtcl equivalent and ntes DataStre.getTypeNames() /capabilities DataStre.getSchema() /describe/layername Wuld use bth the caps and describe t build the result (crs cmes frm caps) FeatureSurce.getQueryCapabilities() Shuld list the ability t perfrm srting and ffsets natively FeatureSurce.getFeatures(Query/Filter) /data/layername?mde=features&... Shuld take the filter and split it int tw parts, the ne natively supprted, and the ne that is perfrmed later in memry. Als, it shuld pass dwn the view params cntained in the Hints.VIRTUAL_TABLE_PARAMETERS hint. FeatureSurce.getBunds(Query) /data/layername?mde=bunds&... Shuld build a ReferencedEnvelpe using the CRS attached t the FeatureType gemetry. Shuld als pass dwn the hints as they might cntain ut f band extra filtering that cannt be encded in the simple native filtering abilities Page 11 f 12

12 FeatureSruce.getCunt(Query) /data/layername?mde=cunt&... Shuld als pass dwn the hints Page 12 f 12