spatialite-gui: Update of "OSM Berlin Surprises"

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Overview

Artifact ID:	d51d8984cdcc187371d68a9da3d6911339432ee9
Page Name:	OSM Berlin Surprises
Date:	2022-06-04 09:44:41
Original User:	sandro
Next	51155bfcd1b6a229e10f9961586ad16c721c18c7

Content

Back to OSM Berlin Index

Where we are

Since now in this tutorial we've simply examined the external skin of the Rendering Engine implemented by librasterlite2 and directly integrated in spatialite_gui via its Map Panel.
It's now time to come down to greater depth so to appreciate all the revolutionary power it can offer.

Be prepared for unexpected surprises.

First surprise: Styled Maps can be created by pure SQL statements

The Rendering Engine (and all that it implies in terms of Styled Map Layers) is fully implemented by librasterlite2, that actually is a dymanic extension expanding the basic SQL capabilities of SQLite.
This practically means that complex richly styled Maps can be created in the easiest way by just executing some appropriate SQL statement.

Such a capability immediately opens the doors for an easy and simple integration of the Rendering Engine in whatever programming language: C/C++, Java, Python, PHP and many others.
The basic approach will always be exactly the same for all them:

Establish a connection to the SQLite database containing the Map by using the language bindings for your specific language.
Then load both extensions SpatiaLite and RasterLite2
Now you'll be ready for executing any RasterLite2 SQL function returning a Styled Map
- Each function will then return a BLOB object containing the image corresponding to your request.
- At this point your program will simply take some appropriate action (as e.g. displaying the image on the screen) and that's all.

Said in other words: developing a feature rich Map Viewer tool will just require to implement the interactive zoom and pan logic.
Any other related task will then directly delegated to the SQL level. Your program will be just required to manage some appropriate SQL query

Support for some kind of SQLite connector being enabled to dynamically load extension modules.
Installing both SpatiaLite and RasterLite2 extensions.

A practical example based on the OSM Berlin Map

SELECT RL2_GetImageFromMapConfiguration('osm-berlin', 
       BuildMbr(391981.48944364, 5820790.78669314, 392990.18818636, 5821799.48543586, 25833), 
       1024, 1024, 
       'image/png');

the first argument corresponds to the Map Configuration name (expected to exists into the connected database).
the second argument corresponds to the Bounding Box to be covered by the image to be created.
the third and fourth arguments respectively are the width and heigth (in pixels) pf the image.
and finally the fifth argumets is the MIME type identified the format of the BLOB image to be returned.
The following MIME types are supported:
- image/png TRUE color (RGB) PNG
- image/png8 grayscale or palette based PNG (8 bits X pixel)
- image/gif GIF
- image/jpeg JPEG compressed image
- image/tiff TRUE color (RGB) TIFF
- image/tiff8 grayscale or palette based TIFF (8 bits X pixel)
- image/geotiff TRUE color (RGB) GeoTIFF
- image/geotiff8 grayscale or palette based GeoTIFF (8 bits X pixel)
- application/pdf or application/x-pdf PDF document
- image/vnd.rl2rgba a flat RGBA matrix of HEIGHT scanlines (from top to bottom)
  Each scanline contains WIDTH pixels (from left to right)
  Pixels are strictly packed, each one of them requiring 4 bytes. (Red, Green, Blue and Alpha channels).
  Note: this specific format usually corresponds to the native one supported by many screen devices.

This is the PNG image returned by the previous SQL Query.

Second surprise: Styled Maps are always ready to be immediately published as WMS - Web Map Services

More precisely, it just requires to create an XLM file defining the WMS service you intend to publish on the WEB.
Dpn't worry, it's a very simple step fully supported by a specific GUI Wizard

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<?xml version="1.0" encoding="UTF-8"?>
<!-- created by spatialite_gui on 2022-06-04 11:08:51 -->
<WmsLiteConfig version="1.0"
  xmlns="http://www.gaia-gis.it/WmsLiteConfig" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xsi:schemaLocation="http://www.gaia-gis.it/WmsLiteConfig http://www.gaia-gis.it/WmsLiteConfig_1_0.xsd" >
	<Service>
		<Name>WMS</Name>
		<Title>WmsLite test server</Title>
		<Abstract>A simple light-weight WMS server for testing RasterLite2 Coverages.</Abstract>
		<KeywordList>
				<Keyword>some keyword</Keyword>
				<Keyword>another keyword</Keyword>
		</KeywordList>
		<OnlineResource>http://localhost:8080/wmslite?</OnlineResource>
		<ContactInformation>
			<ContactPersonPrimary>
				<ContactPerson>James T. Kirk</ContactPerson>
				<ContactOrganization>United Federation of Planets, Starfleet</ContactOrganization>
			</ContactPersonPrimary>
			<ContactPosition>Starship Captain</ContactPosition>
			<ContactAddress>
				<AddressType>stellar</AddressType>
				<Address>USS Enterprise</Address>
				<City>Planet Earth</City>
				<StateOrProvince>Solar System</StateOrProvince>
				<PostCode>12345#WYZ47NL@512</PostCode>
				<Country>Milky Way Galaxy</Country>
			</ContactAddress>
			<ContactElectronicMailAddress>positron@antimatter.org</ContactElectronicMailAddress>
		</ContactInformation>
		<Fees>none</Fees>
		<AccessConstraints>none</AccessConstraints>
		<LayerLimit>10</LayerLimit>
		<MaxWidth>5000</MaxWidth>
		<MaxHeight>5000</MaxHeight>
	</Service>
	<GeneralOptions>
		<MultiThreading Enabled="true" MaxThreads="8" />
		<WMS MaxRetries="5" Pause="5" />
		<Background Color="#f2efe9" Transparent="false" />
		<LabelAdvancedOptions AntiCollisionEnabled="true" WrapTextEnabled="true" AutoRotateEnabled="false" ShiftPositionEnabled="false" />
	</GeneralOptions>
	<WmsLayers>
		<TopLevelLayer>
			<Title>Top Level Layer</Title>
		</TopLevelLayer>
		<MainDB Path="C:\Users\afuri\Downloads\osm\berlin_osm.sqlite">
			<Layer Alias="osm-berlin" Name="osm-berlin" Type="MapConfiguration" Child="false" >
				<ChildLayer>forests</ChildLayer>
				<ChildLayer>water_bodies</ChildLayer>
				<ChildLayer>agriculture</ChildLayer>
				<ChildLayer>green_areas</ChildLayer>
				<ChildLayer>buildings</ChildLayer>
				<ChildLayer>religion</ChildLayer>
				<ChildLayer>rivers</ChildLayer>
				<ChildLayer>cemeteries</ChildLayer>
				<ChildLayer>motorway</ChildLayer>
				<ChildLayer>trunk</ChildLayer>
				<ChildLayer>rd_primary</ChildLayer>
				<ChildLayer>rd_secondary</ChildLayer>
				<ChildLayer>rd_tertiary</ChildLayer>
				<ChildLayer>rd_residential</ChildLayer>
				<ChildLayer>paths</ChildLayer>
				<ChildLayer>cycleways</ChildLayer>
				<ChildLayer>subway</ChildLayer>
				<ChildLayer>rail</ChildLayer>
				<ChildLayer>light_rail</ChildLayer>
				<ChildLayer>tram</ChildLayer>
				<ChildLayer>suburbs</ChildLayer>
				<ChildLayer>railway_stations</ChildLayer>
				<ChildLayer>tram_stops</ChildLayer>
			</Layer>
			<Layer Alias="agriculture" Name="agriculture" Type="VectorCoverage" Child="true" />
			<Layer Alias="buildings" Name="buildings" Type="VectorCoverage" Child="true" />
			<Layer Alias="cemeteries" Name="cemeteries" Type="VectorCoverage" Child="true" />
			<Layer Alias="cycleways" Name="cycleways" Type="VectorCoverage" Child="true" />
			<Layer Alias="forests" Name="forests" Type="VectorCoverage" Child="true" />
			<Layer Alias="green_areas" Name="green_areas" Type="VectorCoverage" Child="true" />
			<Layer Alias="light_rail" Name="light_rail" Type="VectorCoverage" Child="true" />
			<Layer Alias="motorway" Name="motorway" Type="VectorCoverage" Child="true" />
			<Layer Alias="paths" Name="paths" Type="VectorCoverage" Child="true" />
			<Layer Alias="rail" Name="rail" Type="VectorCoverage" Child="true" />
			<Layer Alias="railway_stations" Name="railway_stations" Type="VectorCoverage" Child="true" />
			<Layer Alias="rd_primary" Name="rd_primary" Type="VectorCoverage" Child="true" />
			<Layer Alias="rd_residential" Name="rd_residential" Type="VectorCoverage" Child="true" />
			<Layer Alias="rd_secondary" Name="rd_secondary" Type="VectorCoverage" Child="true" />
			<Layer Alias="rd_tertiary" Name="rd_tertiary" Type="VectorCoverage" Child="true" />
			<Layer Alias="religion" Name="religion" Type="VectorCoverage" Child="true" />
			<Layer Alias="rivers" Name="rivers" Type="VectorCoverage" Child="true" />
			<Layer Alias="suburbs" Name="suburbs" Type="VectorCoverage" Child="true" />
			<Layer Alias="subway" Name="subway" Type="VectorCoverage" Child="true" />
			<Layer Alias="tram" Name="tram" Type="VectorCoverage" Child="true" />
			<Layer Alias="tram_stops" Name="tram_stops" Type="VectorCoverage" Child="true" />
			<Layer Alias="trunk" Name="trunk" Type="VectorCoverage" Child="true" />
			<Layer Alias="water_bodies" Name="water_bodies" Type="VectorCoverage" Child="true" />
		</MainDB>
	</WmsLayers>
</WmsLiteConfig>

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