gml:DirectPositionListType

[Farrukh Najmi]

Dear colleagues,

I am not sure if this is off topic. If so please refer me to a more
appropriate forum for general GML 3 spec questions.

My immediate question is regarding DirectPositionListType. It has a list
of doubles which need at least
srsDimension to be interpretted properly (ie. coordinate count is
srsDimension / size of list).

Spec for GML 3.2.1 says in 10.4.1.2 that srsDimension and count are
optional:

"
The optional attribute count specifies the number of direct positions in
the list. If the attribute count is present
then the attribute srsDimension shall be present, too.
The number of entries in the list is equal to the product of the
dimensionality of the coordinate reference system
(i.e. it is a derived value of the coordinate reference system
definition) and the number of direct positions.
"

My questions are:

    * How can an app process the list of doubles in a
      DirectPositionListType without knowing the srsDimension? Is there
      a default of 2 when it is not specified? If so, where is the
      default mentioned?
    * Why is a count attribute needed if there is an srsDimension
      specified. Would the count not simply be calculated as (size of
      list ) / srsDImension?
    * How does one interpret a gml:posList like one below when there is
      no srsDimension or count available?
      <gml:posList>45.256 -110.45 46.46 -109.48 43.84 -109.86 45.256
      -110.45</gml:posList>

TIA for clarifying this.

--
Regards,
Farrukh Najmi

Web: http://www.wellfleetsoftware.com


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[David Burggraf]

Farrukh

I think the gml.sig may be the best forum for these questions, I have
forwarded this to that email list and will answer it there.

David.

-----Original Message-----
From: georss-bounces@...
[mailto:georss-bounces@...] On Behalf Of Farrukh Najmi
Sent: May-21-08 12:10 PM
To: georss@...
Subject: [georss] gml:DirectPositionListType

Dear colleagues,

I am not sure if this is off topic. If so please refer me to a more
appropriate forum for general GML 3 spec questions.

My immediate question is regarding DirectPositionListType. It has a list

of doubles which need at least
srsDimension to be interpretted properly (ie. coordinate count is
srsDimension / size of list).

Spec for GML 3.2.1 says in 10.4.1.2 that srsDimension and count are
optional:

"
The optional attribute count specifies the number of direct positions in

the list. If the attribute count is present
then the attribute srsDimension shall be present, too.
The number of entries in the list is equal to the product of the
dimensionality of the coordinate reference system
(i.e. it is a derived value of the coordinate reference system
definition) and the number of direct positions.
"

My questions are:

    * How can an app process the list of doubles in a
      DirectPositionListType without knowing the srsDimension? Is there
      a default of 2 when it is not specified? If so, where is the
      default mentioned?
    * Why is a count attribute needed if there is an srsDimension
      specified. Would the count not simply be calculated as (size of
      list ) / srsDImension?
    * How does one interpret a gml:posList like one below when there is
      no srsDimension or count available?
      <gml:posList>45.256 -110.45 46.46 -109.48 43.84 -109.86 45.256
      -110.45</gml:posList>

TIA for clarifying this.

--
Regards,
Farrukh Najmi

Web: http://www.wellfleetsoftware.com


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[Carl Reed]

Farrukh -

I would suggest the OGC GML WG email list: gml.sig@...

Cheers

Carl

----- Original Message -----
From: "Farrukh Najmi" <farrukh@...>
To: <georss@...>
Sent: Wednesday, May 21, 2008 1:10 PM
Subject: [georss] gml:DirectPositionListType

> Dear colleagues,
>
> I am not sure if this is off topic. If so please refer me to a more
> appropriate forum for general GML 3 spec questions.
>
> My immediate question is regarding DirectPositionListType. It has a list
> of doubles which need at least
> srsDimension to be interpretted properly (ie. coordinate count is
> srsDimension / size of list).
>
> Spec for GML 3.2.1 says in 10.4.1.2 that srsDimension and count are
> optional:
>
> "
> The optional attribute count specifies the number of direct positions in
> the list. If the attribute count is present
> then the attribute srsDimension shall be present, too.
> The number of entries in the list is equal to the product of the
> dimensionality of the coordinate reference system
> (i.e. it is a derived value of the coordinate reference system
> definition) and the number of direct positions.
> "
>
> My questions are:
>
>    * How can an app process the list of doubles in a
>      DirectPositionListType without knowing the srsDimension? Is there
>      a default of 2 when it is not specified? If so, where is the
>      default mentioned?
>    * Why is a count attribute needed if there is an srsDimension
>      specified. Would the count not simply be calculated as (size of
>      list ) / srsDImension?
>    * How does one interpret a gml:posList like one below when there is
>      no srsDimension or count available?
>      <gml:posList>45.256 -110.45 46.46 -109.48 43.84 -109.86 45.256
>      -110.45</gml:posList>
>
> TIA for clarifying this.
>
> --
> Regards,
> Farrukh Najmi
>
> Web: http://www.wellfleetsoftware.com
>
>
> _______________________________________________
> georss mailing list
> georss@...
> http://lists.eogeo.org/mailman/listinfo/georss

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[joshli]

Farrukh,

This question came up in terms of GeoRSS GML. The srsDimension and  
count are optional because the dimensions and hence the coordinate  
count should be determined by the CRS (specifically the CS). The  
optional parameters are a convenience.

Specifically for GeoRSS GML, the default CRS is WGS 84 latitude-
longitude decimal degrees, meaning one latitude coordinate followed by  
one longitude coordinate in each tuple.

Cheers,

Josh

On May 21, 2008, at 3:10 PM, Farrukh Najmi wrote:

> Dear colleagues,
>
> I am not sure if this is off topic. If so please refer me to a more
> appropriate forum for general GML 3 spec questions.
>
> My immediate question is regarding DirectPositionListType. It has a  
> list
> of doubles which need at least
> srsDimension to be interpretted properly (ie. coordinate count is
> srsDimension / size of list).
>
> Spec for GML 3.2.1 says in 10.4.1.2 that srsDimension and count are
> optional:
>
> "
> The optional attribute count specifies the number of direct  
> positions in
> the list. If the attribute count is present
> then the attribute srsDimension shall be present, too.
> The number of entries in the list is equal to the product of the
> dimensionality of the coordinate reference system
> (i.e. it is a derived value of the coordinate reference system
> definition) and the number of direct positions.
> "
>
> My questions are:
>
>    * How can an app process the list of doubles in a
>      DirectPositionListType without knowing the srsDimension? Is there
>      a default of 2 when it is not specified? If so, where is the
>      default mentioned?
>    * Why is a count attribute needed if there is an srsDimension
>      specified. Would the count not simply be calculated as (size of
>      list ) / srsDImension?
>    * How does one interpret a gml:posList like one below when there is
>      no srsDimension or count available?
>      <gml:posList>45.256 -110.45 46.46 -109.48 43.84 -109.86 45.256
>      -110.45</gml:posList>
>
> TIA for clarifying this.
>
> --
> Regards,
> Farrukh Najmi
>
> Web: http://www.wellfleetsoftware.com
>
>
> _______________________________________________
> georss mailing list
> georss@...
> http://lists.eogeo.org/mailman/listinfo/georss

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