Demystifying Web Map Servers

Transcript

1. Demystifying Web Map Servers: the invisible side of Geographic Information Systems - Shivashis Padhi
2. What is common among the products listed below? plant99_ CC-BY-SA 4.0
3. https://unsplash.com/@andrewtneel
5. Geographic Information System? Maps, how are they generated? Yes, but what is the need to separate maps and map-servers? plant99_ CC-BY-SA 4.0
6. http connection WMS Map Client Architecture plant99_ CC-BY-SA 4.0
7. What this talk would be about? ➔ Basic Geography and terminologies ➔ Creating maps ➔ Geo-data storage/manipulation options ➔ Web Map Servers What this talk would not be about? ➔ Commercial usage, scaling Outline plant99_ CC-BY-SA 4.0
8. ➔ Projections ➔ Coordinates Reference System ➔ Layers ➔ Type of view ➔ Legend plant99_ CC-BY-SA 4.0 Maps primer
9. plant99_ CC-BY-SA 4.0 https://demo.mapserver.org/cgi-bin/wms?SERVICE =WMS&VERSION=1.1.1&REQUEST=GetMap&BBOX= 0,-90,180,90&SRS=EPSG:4326&WIDTH=953&HEIGH T=480&LAYERS=bluemarble,cities&STYLES=&FORM AT=image/png&TRANSPARENT=true Sample WMS access URL
10. Coordinate Reference System ➔ Map projections try to portray the surface of the earth or a portion of the earth on a flat piece of paper or computer screen. ➔ A coordinate reference system (CRS) then defines, with the help of coordinates, how the two-dimensional, projected map in your GIS is related to real places on the earth. plant99_ CC-BY-SA 4.0
11. Projection Source - https://docs.qgis.org ➔ Distortions ➔ Area, direction, angle(form), distance plant99_ CC-BY-SA 4.0
12. Coordinate Reference Systems Source - https://docs.qgis.org ➔ Geographic CRS ➔ Projected CRS plant99_ CC-BY-SA 4.0
13. Layers ➔ Different types of data which can be represented by a map. ➔ Why do we need ‘layers’? To optimize queries. ➔ Example plant99_ CC-BY-SA 4.0
14. Demonstration of different layers being added to the maps plant99_ CC-BY-SA 4.0
15. Type of views ➔ Top view ➔ Side view How does this affect the image generation? Where are each used? plant99_ CC-BY-SA 4.0
16. Topview Sideview plant99_ CC-BY-SA 4.0
17. Legend Image ➔ Description of legend image ➔ Examples of legend Image plant99_ CC-BY-SA 4.0
18. A short detour to understand custom maps plant99_ CC-BY-SA 4.0
19. ➔ Raster ➔ Vector Types of storage plant99_ CC-BY-SA 4.0
20. ➔ Gridded data ➔ Each grid represents a data-point ➔ E.g/ NetCDF, GeoTIFF Raster Data Image courtesy: https://annefou.github.io/metos_python/fig/raster_concept.png plant99_ CC-BY-SA 4.0
21. ➔ discrete geometric locations(vertices) defining ‘shape’. ➔ E.g/ Shapefile, GeoJSON Vector Data Image courtesy: https://github.com/annefou/metos_python/blob/gh-pages/data/no-all-all .geojson plant99_ CC-BY-SA 4.0
22. ➔ 4D data in .csv ➔ A more efficient option ➔ Parallelization of data-access ➔ Identified by .nc extension NetCDF plant99_ CC-BY-SA 4.0
23. ➔ https://bit.ly/merra2 ➔ ncview to visualize .nc files quickly ➔ ncview on merra2 dataset, to visualize `t2m` variable. A small exercise plant99_ CC-BY-SA 4.0
24. ➔ Projections, background ➔ Easy APIs drawoceans(), drawcontinents() ➔ drawlabels() ➔ Plot with contour()/plot() ➔ More at https://matplotlib.org/basemap/users/intro.html ➔ Migration to https://scitools.org.uk/cartopy/docs/latest/ Basemap package - matplotlib plant99_ CC-BY-SA 4.0
25. ➔ Code to plot merra2.nc data on map ➔ 2D array as final input ➔ Figure out what to plot, in case of 3D, 4D data. Plot data on a map plant99_ CC-BY-SA 4.0
26. ➔ Code to ecwmf data plot ➔ How is the map created? ➔ Raster/Vector basemap. Pressure dataset for a part of world map plant99_ CC-BY-SA 4.0
27. Components of WMS plant99_ CC-BY-SA 4.0
28. Standards, but why? plant99_ CC-BY-SA 4.0
29. https://www.opengeospatial.org/stand ards/wms#overview Link to wms standards pdf plant99_ CC-BY-SA 4.0
30. GetCapabilities ➔ What is GetCapabilites request? ➔ /?service=WMS&request=GetCapabilities&version=1. 1.1 ➔ Code plant99_ CC-BY-SA 4.0
31. GetMap ➔ What is GetMap request? ➔ Demo url for GetMap ➔ Code plant99_ CC-BY-SA 4.0
32. GetVSecMap ➔ What is GetVSec request? ➔ Demo url for GetVSec ➔ Code plant99_ CC-BY-SA 4.0
33. Demonstration of a WMS with GIS client plant99_ CC-BY-SA 4.0
34. How does Python fare in this sector? ➔ Why should one need Python anyway to develop WMS? (extensible, easy) ➔ Why should you contribute? (give back) ➔ How can you contribute? ogc(standards), basemap, cartopy, mss, metpy, Open Street Map plant99_ CC-BY-SA 4.0
35. Thank you! :) Questions? plant99_ Source of background image: https://www.fooa.org shivashispadhi@gmail.com plant99_