[Proj] placing a matplotlib basemap plot on a google map

[Joaquim Luis]

If you are on Windows and you are lucky that the file internals are  
recognized the easiest way is to use Mirone (w3.ualg.pt/~jluis/mirone). A  
simple drag-n-drop plus a click on the GE icon should do the job. (but  
you'll need to update with "Help -> check for updates).

Another option is to reproject  with gdalwarp and use GMT to produce a  
nice image and a kml (the ps2raster (now called psconvert) module)

Joaquim

> Hi
>
> For quite some time now I've been wresteling with a problem concerning  
> projections. I was wondering if the experts on >this forum/mailinglist  
> could be of any help, since (let's face it) the material is quite  
> frankly over my head.
>
> The short story is that I have got an hdf5 radar image, which contains  
> an x-y grid of pixelvalues and I have to place it >on a google map.  
> Already there's a problem because the data is purely an x-y grid and  
> google maps uses the EPSG >3857projection. The proj4 string provided in  
> the hdf5 file is one of the RD-coordinate system, a system used in the  
> >Netherlands.
>
> The rest of the information I can find is listed here
>
> cal_data_count = 0
> cal_method = None
> cal_stations_count = 0
> composite_count = 288
> declutter_history = 0.1
> declutter_size = 4.0
> fill_value = -9999
> grid_extent = -110000,390000,700000,210000
> grid_projection = PROJCS["unnamed",GEOGCS["Bessel  
> 1841",DATUM["unknown",SPHEROID>["bessel",6377397.155,299.1528128],TOWGS84[565.237,50.0087,465.658,-0.406857,0.350733,-1.87035,4.0812]],PRIMEM>["Greenwich",0],UNIT["degree",0.0174532925199433]],PROJECTION["Oblique_Stereographic"],PARAMETER>["latitude_of_origin",52.15616055555555],PARAMETER["central_meridian",5.38763888888889],PARAMETER>["scale_factor",0.999908],PARAMETER["false_easting",155000],PARAMETER["false_northing",463000],UNIT["Meter",1]]
> grid_size = 500,490
> locations =  
> >-7384.887748796755,358296.0214553905,140661.4380856066,456959.9690822229,115509.8972636278,551852.1442379927,263965.23587302887,595812.4921183779,264883.22682543105,380702.99609763426,238048.54530185566,236013.44861746818
> method = weighted lowest altitudes
> radars = JAB,NL60,NL61,emd,ess,nhb
> ranges = 298.75,239.5,239.5,127.5,127.5,127.5
> timestamp_first_composite = 20151211080000
> timestamp_last_composite = 20151212075500
>
> map_projection (6024, 2)
> Group size = 0
> Number of attributes = 3
> projection_indication = Y
> projection_name = STEREOGRAPHIC
> projection_proj4_params = +proj=sterea +lat_0=52.15616055555555  
> +lon_0=5.38763888888889 +k=0.999908 >+x_0=155000 +y_0=463000  
> +ellps=bessel  
> +towgs84=565.237,50.0087,465.658,-0.406857,0.350733,-1.87035,4.0812  
> >+units=m +no_defs
>
> geographic (5200, 2)
> Group size = 1
> Number of attributes = 8
> geo_dim_pixel = KM,KM
> geo_number_columns = 500
> geo_number_rows = 490
> geo_par_pixel = X,Y
> geo_pixel_def = CENTRE
> geo_pixel_size_x = 1.0
> geo_pixel_size_y = -1.0
> geo_product_corners =  
> -110000,210000,-110000,700000,390000,700000,390000,210000
> Right now I am using a complex code to rewrite each of the pixels to  
> lat/lon & I plot them with matplotlib (python) on a >mpl basemap without  
> landcontours, coast-contours so I have an image on an mpl-basemap, but  
> as said, without the >countrycontours & such. The projecction used for  
> the Basemap is "mercator". The result gives the desired radarimage &  
> >seems to match the locations... so far so good but with the python  
> mapping of pixels to lat/lons...
>
> I then run the output (a png file) through gdal to tile it, & warp it to  
> the EPSG 3857 projection (Gmaps). When turning >on the country-contours  
> to check the result, the result is not correct, although it comes close  
> to what it should be.
>
> http://postimg.org/image/ly01obb1n/
>
> I am starting to wonder if there's another way I can make this work,  
> perhaps without the use of matplotlib python? Eg, >going from the  
> standard x-y grid Hdf5 data straight to a warp using gdal or whichever  
> way possible. I have run out of >ideas & the information I can find to  
> help me get passed this is really confusing.
>
>
> I am looking forward to the reply of the masters in this forum.
>
>
> Best regards
>
> D.
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