lost attributes after running calculate_param()

[adokter]

If we add a scan parameter CELL as follows:

data(example_scan)
example_scan_cell <- calculate_param(example_scan,CELL=ifelse(DBZH>0,0,1))

certain function fail on this new scan parameter:

> project_as_ppi(example_scan_cell)
 Error in CRS(paste("+proj=aeqd +lat_0=", attributes(param)$geo$lat, " +lon_0=",  : 
  No spaces permitted in PROJ4 argument-value pairs: +proj=aeqd +lat_0= +lon_0= +units=m 

The reason is that the new parameter has missing attributes, in particular the geo attributes:

> attributes(example_scan_cell$params$CELL)
$dim
[1] 480 360

$param
[1] "CELL"

c.f. DBZH:

> attributes(example_scan_cell$params$DBZH)
$dim
[1] 480 360

$class
[1] "param"  "matrix"

$radar
[1] "SE50"

$datetime
[1] "2015-10-18 18:00:00 UTC"

$geo
$geo$lat
[1] 56.3675

$geo$lon
[1] 12.8517

$geo$height
[1] 209

$geo$elangle
[1] 0.5

$geo$rscale
[1] 500

$geo$ascale
[1] 1


$param
[1] "DBZH"

[bart1]

I encountered the same problem recently, the problem is some R functions like logical operations strip all attributes. One option it to later set attributes again if they are lost. The problem is that the input data can be quite diverse so it it not directly clear what attributes should be placed. e.g. what to do if not all input params of a scan have the same attributes?

[adokter]

@bart1 the dim, class, radar, datetime and geo attributes should always be the same (but indeed can differ in theory if people paste together their own class object). How about checking that these attributes are present at the end of calculate_param() and if they are missing copy them from the first quantity in the expression generating the new parameter?

[adokter]

fixed by #408