Unspecified image with WCS

[swood-ecology]

Hi, when I try to get coverage data from an FAO server I get either an internal error or an external one related to an unspecified image.

Here's the setup code:

require(ows4)

# Create WCS Client
WCS <- WCSClient$new(
  url="https://io.apps.fao.org/geoserver/wcs", 
  serviceVersion="1.1.1", 
  logger="INFO"
)

# Get capabilities
caps <- WCS$getCapabilities()

# Get coverage summary
cov <- caps$findCoverageSummaryById("GLEAM3:a_prod")

# Describe a coverage
cov_des <- cov$getDescription()

Here's where I request the data:

# Get coverage data
cov_data <- cov$getCoverage()

This gives the following error:

> cov_data <- cov$getCoverage()
Error in `.rowNamesDF<-`(x, value = value) : invalid 'row.names' length

I figured this might be an issue of not having a bounding box, so I created a global one:

# Try with global bounding box
box <- OWSUtils$toBBOX(180,90,-180,-90)
cov_data <- cov$getCoverage(bbox=box)

This produced the following error:

> cov_data <- cov$getCoverage(bbox=box)
[ows4R][WARN] WCSCoverageSummary - Coverage without temporal dimension: 'time' argument is ignored 
[ows4R][WARN] WCSCoverageSummary - Coverage without vertical dimension: 'elevation' argument is ignored 
[ows4R][INFO] WCSGetCoverage - Fetching https://io.apps.fao.org/geoserver/wcs?service=WCS&version=1.1.1&identifier=GLEAM3:a_prod&boundingbox=-180,180,-90,90,urn:ogc:def:crs:EPSG::4326&format=image/tiff&request=GetCoverage 
Downloading: 300 B     [ows4R][ERROR] WCSCoverageSummary - Error while getting coverage: org.geotools.coverage.grid.InvalidGridGeometryException: Unspecified image&apos;s size.
Unspecified image&apos;s size. 

Does anyone have any insight into what I might be doing wrong?

[eblondel]

I'm looking at it; From what I see, this is not a problem with the getCoverage but rather with the decoding of the coverage description, for which some element (envelope) is not well handled.

[swood-ecology]

Does that mean it's something that I'm doing wrong in not knowing what to pass to the getCoverage function? Or is it something missing in the data from FAO?

[eblondel]

You don't do anything wrong; It could be an issue with the way Geoserver encodes the coverage description, this one in particular, or even some bug in ows4R :-)

[eblondel]

I could make it work using version 2.0.1 of the WCS service. One note when using version 2 the separator between the namespace and the layer name is not : but a double underscoe __. Layer name would be GLEAM3__a_prod.

I realized this server fails 1 out of 2 attempts to get coverage. Don't be surprised if the first request fails, in general the 2d works. I suspect they have a load balancer that delegates request to one service instance that is down behind, which would explain why 1 request out of 2 is failing.

See this code

require(ows4R)

# Create WCS Client
WCS <- WCSClient$new(
  url="https://io.apps.fao.org/geoserver/wcs", 
  serviceVersion="2.0.1", 
  logger="INFO"
)

# Get capabilities
caps <- WCS$getCapabilities()

# Get coverage summary
cov <- caps$findCoverageSummaryById("GLEAM3__a_prod")

# Describe a coverage
cov_des <- cov$getDescription()

# Get coverage
cov_data <- cov$getCoverage()

# plot
require(terra)
plot(cov_data)