dhis2-devs team mailing list archive

[Knut Staring <knutst@xxxxxxxxx>]

2010/7/14 Lars Helge Øverland <larshelge@xxxxxxxxx>:
>
> We are in the process of changing the GIS module in terms of how the
> geographical information is persisted and presented.
> In the snapshot version we now store the coordinates in JSON format directly
> in the database on the OrganisationUnit.coordinates property. This gives us
> a lot more flexibility in the way maps are presented.
> Previously maps had to be registered explicitly either in the form of
> GeoJson files or Shapefiles. Then the user had to select a map together with
> indicator and period. Now the user can select an orgunit from a tree and the
> children of that orgunit at the level below will be displayed in the map.
> In large countries in India it is impossible to display a single map at the
> lower levels (eg. for thousands of districts) as the map will be too heavy
> and slow to load. Registering and managing maps for every e.g. provinces
> will also be too cumbersome. With the current solution there is no more work
> of registering and selecting maps - only the one time job of importing
> geographical data/coordinates into the database.
> Importing is a 4 step process:
>
> 1. Convert your shapefiles (or whatever format you have) into GML.
> The recommended tool is FWTools, http://fwtools.maptools.org/ ;. The command
> for converting shapefiles into GML is
> ogr2ogr -F GML output.gml input.shp

One problem is that the conversion to GML seems to generate very large
representations, because the GML coordinates are output with 15
decimals, whereas you would normally be happy with 5-6. Here is a
comparison of what I get in GeoJSON vs GML (converting from the same
shapefile):
GeoJSON: 38.415412, 1.750212
GML:        38.415411724082148,1.750212388592194
																							
It also seems that there the import process puts a bit too many
brackets on points:
Example point representation (which also has a ridiculous tail of decimals):
[[[[37.270000000000003,-0.69]]]]

Example full polygon representation (gets very big when adding
hundreds of polygons into a layer):
[[[[35.241617396557501,-1.042755167363498],[35.082178302163747,-0.910721897610392],[35.016946729972211,-0.895020643910023],[35.011665399182093,-0.885742630359804],[35.024369140812389,-0.87746378749961],[35.019944242042286,-0.853483690939046],[35.045208986632879,-0.856766680349123],[35.060339285653235,-0.839352562608713],[35.077610664723643,-0.860192408429204],[35.085033075563814,-0.846061280098871],[35.139987463515105,-0.881032254249694],[35.136418996765023,-0.843206506698804],[35.168249720175773,-0.842064597338777],[35.172674618945877,-0.792391540177609],[35.202078784966567,-0.793390710867632],[35.231625689657264,-0.819083671468237],[35.262599981047991,-0.804667065797898],[35.297285477858807,-0.830645503738509],[35.334540270729683,-0.814087818018119],[35.343961022949905,-0.790393198797562],[35.27601741602831,-0.724162455916004],[35.242759305917524,-0.747857075136561],[35.241331919217494,-0.694758289895313],[35.262029026367976,-0.680056206884967],[35.291861408398681,-0.655076939634379],[35.387496317300929,-0.65935909973448],[35.397773501541174,-0.647940006134211],[35.420611688741708,-0.729301048036125],[35.481989316843155,-0.77797493450727],[35.539513000854505,-0.798101086977743],[35.434029123722027,-0.895020643910023],[35.408478901791426,-0.957111965361483],[35.360233231330291,-0.98123480059205],[35.346673057679972,-0.973812389751876],[35.241617396557501,-1.042755167363498]]]]