[mapserver-users] WMS from netCDF returns white/transparent image

[Bill Hudspeth]

I think there is an issue with the fact that a request for a single layer from a netCDF file may contain multiple bands.... In QGIS, the WMS services capability brings in a single layer (with multiple bands) as "Singleband Color Data". The image is transparent. When I request the layer with a URL, and I use the &Bands=1 (or 2,3,4), I get a white image....

Bill

----- Original Message -----
From: "bhudspeth" <bhudspeth at edac.unm.edu>
To: mapserver-users at lists.osgeo.org
Sent: Monday, June 22, 2015 3:35:27 PM
Subject: Re: [mapserver-users] WMS from netCDF returns white/transparent image

TC

Thank you for your help...I have tried building classes into the layer definition with the same results...a white image. Also used the CLASSITEM "[pixel]" parameter. I can import the layer into QGIS, and it actually shows the colors I define in the legend, and is projected correctly, but the image is invisible....I've not seen something like this before!

Bill

----- Original Message -----
From: "bhudspeth" <bhudspeth at edac.unm.edu>
To: mapserver-users at lists.osgeo.org
Sent: Monday, June 22, 2015 9:51:16 AM
Subject: [mapserver-users] WMS from netCDF returns white/transparent image

Hello, 

I am trying to generate WMS services from layers in a NetCDF file. WCS services already work well...While a WMS call does return an image (ex. PNG), it is all white or transparent, whereas a WCS call to the same layer returns an image with a range of pixel values. I have run gdalinfo on the layer to get the data range, and have tried using the data range to set the PROCESSING DIRECTIVE to scale the output (e.g. PROCESSING "SCALE=311.76470947266 ,423.52941894531 " ). I have also used the SCALE=AUTO directive, but both just return a white image. When I try using WMS on this layer in QGIS, it is correctly projected, but invisible (zoom to extents on the imported WMS layer is correct). Below is the output from gdalinfo to get the original data range, and then the mapfile entry for the layer to see how I have set this up.... 

gdalinfo NETCDF:"flat_sample.nc":I_lw 

Band 1 Block=170x1 Type=Float32, ColorInterp=Undefined Min=311.765 Max=423.529 
Minimum=311.765, Maximum=423.529, Mean=344.247, StdDev=16.599 
NoData Value=9.96920996838686905e+36 
Metadata: 
ipw_desc=incoming thermal (long-wave) radiation 
NETCDF_DIM_time=14 
NETCDF_VARNAME=I_lw 
standard_name=downwelling_longwave_flux_in_air 
STATISTICS_MAXIMUM=423.52941894531 
STATISTICS_MEAN=344.24709697293 
STATISTICS_MINIMUM=311.76470947266 
STATISTICS_STDDEV=16.598777681661 
units=W m-2 

******************************************************************************** 

LAYER DATA 'NETCDF:"/geodata/watershed-data/8c/8c18e10f-44b0-4462-bf4f-1c27c984aece/flat_sample.nc":I_lw' 
EXTENT -116.142905556 43.7294055556 -116.137583333 43.7326972222 
METADATA 
"wcs_label" "downwelling_longwave_flux_in_air" 
"layer_title" "downwelling_longwave_flux_in_air" 
"raster_selected" "yes" 
"wms_metadataurl_type" "FGDC-STD-001-1998" 
"ows_keywordlist" "" 
"wcs_formats" "GEOTIFF_16" 
"background" "no" 
"wcs_bands_description" "ISNoBal Timesteps 1-16" 
"ows_abstract" "incoming thermal (long-wave) radiation" 
"wcs_rangeset_name" "Timesteps" 
"wms_metadataurl_href" "http://129.24.63.85//apps/vwp/datasets/05e73f4f-51d3-417c-9757-e376b5969a9c/metadata/FGDC-STD-001-1998.xml" 
"wcs_bands_values" "1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16" 
"legend_display" "yes" 
"queryable" "no" 
"wcs_rangeset_label" "netCDF flat_sample.nc" 
"time_sensitive" "no" 
"ows_srs" "epsg:26911" 
"wcs_bands_name" "Timestep" 
"wcs_bands_rangeitem" "_bands" 
"ows_title" "incoming thermal (long-wave) radiation""static" "no" 
"wms_metadataurl_format" "text/xml" 
"wcs_bands_label" "Timestep Number" 
"wcs_rangeset_axes" "bands" 
"wms_encoding" "UTF-8" 
"wcs_enable_request" "*" 
"layer_data_units" "W m-2" 
"annotation_name" "downwelling_longwave_flux_in_air: 2015-06-19 20:30:29.202558" 
END # METADATANAME "downwelling_longwave_flux_in_air" 
PROCESSING "CLOSE_CONNECTION=DEFER" 
PROCESSING "SCALE=311.76470947266 ,423.52941894531 " 
#PROCESSING “SCALE=AUTO” 
PROJECTION 
"init=epsg:26911" 
END # PROJECTION 
STATUS ON 
TILEITEM "location" 
TYPE RASTER 
UNITS METERS 
END # LAYER 

******************************************************************************** 

It seems I am missing something here....would appreciate any insight into how to return a valid image in WMS.... 


Thanks, Bill 




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