[pygeoapi] Process - is it defined how to retrieve single output of a job result ?

Wed Dec 6 09:32:12 PST 2023

Hi Francesco

If I understand the question correctly, then I think table 12 of the OGC
API - Processes standard provides you with the answer. The way that results
are accessed depends on your original processing request:

1. if you requested sync execution, results ought to be transmitted in a
similar way as the one described for async (more on that below)
2. if you requested async execution (or let's say you requested sync, but
want to retrieve the results again), then it depends on a number of factors:

2.1. If response type is 'raw' and transmission mode is 'value' and there
is a single output, then the result will be available at the link indicated
by the 'Location' header in the raw output type (e.g. a geotiff file that
was generated as the result of the process execution)

2.2. If response type is 'raw' and transmission mode is 'value' and there
are a multiple outputs, then the result will be a multipart/related
response with each result being a 'part', and they will be available at the
link indicated by the 'Location' header (e.g. multiple geotiffs generated,
then response will have all of them concatenated, each will be a 'part' of
the message) - This is the same way as an email client would transmit
images via email. Browse the Internet for information on the
'multipart/related' media type in order to know more about this

2.3. If response type is 'raw' and transmission mode is 'reference' and
there are is either a single output or multiple outputs, then when you
visit the resource that the 'Location' header links to you will get back an
empty response body, but the response headers shall contain a 'Link' header
for each output, with the value of the header being a link for each output
where you should be able to get each result in its raw output type (i.e.
there will be a 'Link' header with a link for the actual geotiff generated
as a process result)

2.4. If response type is 'raw' and transmission mode is mixed (i.e. there
are multiple outputs and some of them are to be transmitted by 'value'
while others by 'reference') then the result will again be a
multipart/related resource and presumably there will be one 'part' for each
output that is being transmitted by 'value' and one 'Link' header for each
output being transmitted by 'reference' - I think this is my interpretation
of the standard, it does not actually say this though

2.5. If the response type is 'document', the response will always be a JSON
document that complies with the relevant 'results.yaml' schema (as
mentioned in the standard).

2.5.1 For each generated process result that has its transmission mode
requested as 'value', the actual result is transmitted in the JSON
document. If the result it is a JSON type (int, str, object, etc) then it
is shown directly. If the result is some binary data, then it should be
encoded as a string, maybe using base64, but there is a provision for
specifying the encoding of the data and also the media-type of
theunderlying data - you can check the example 2 provided in section 7.13.2
of the standard for more info on this

2.5.2. For each generated process result that has its transmission mode set
to 'reference' then the response JSON document will include a link to the
resource.

I hope this makes it a bit clearer.

Please note that, as mentioned in a previous message, pygeoapi does not
currently support this form of result retrieval, not yet anyway ;) - it
effectively ignores whatever form of output generation has been (thereby
always assuming response type 'raw' and transmission mode 'value').

As for where to post these kinds of questions, I'm not sure, but maybe you
can open an issue at the standard's github repo? Here:

https://github.com/opengeospatial/ogcapi-processes/issues

I guess asking them here might also be appropriate.

Best regards

Francesco Martinelli via pygeoapi <pygeoapi at lists.osgeo.org> escreveu no
dia quarta, 6/12/2023 à(s) 16:29:

> Hi there,
> I am not sure this is the appropriate mailing list where to ask:
> if this is inappropriate I apologize,
> and if possible I ask to advise where should I post my question.
>
> Reading the OGC API - PROCESSES -Part 1: CORE
> I don't find a way (if possible) to retrieve a single output result from
> a job.
> Specifically I am looking to paragraph 7.13
>
> If I submit an execute request, and I get back a UUID for the job (i.e.
> a 'Location' in the header, where the location contains the UUID/jobID),
> then I can thereafter get the results of the job on the path
> /jobs/{jobID}/results.
>
> However if I had multiple outputs (possibly of sensible size)
> and I want to get only one,
> I don't find a way to get only that single output: is it possible?
> If positive: how to specify this request?
>
>
> Thank you,
> Francesco
> _______________________________________________
> pygeoapi mailing list
> pygeoapi at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/pygeoapi
>

-- 
___________________________ ___ __
Ricardo Garcia Silva
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