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List: fdo-users
Subject: [fdo-users] view scale
From: gavin.cramer () autodesk ! com (Gavin Cramer)
Date: 2008-02-20 15:29:10
Message-ID: 800886C2A4A73E44BA0FE45152C023702505D7116F () ADSK-NAMSG-02 ! MGDADSK ! autodesk ! com
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Artem, check out the SDF Provider for example code. It has an optimized \
implementation for SpatialExtents and Count. In the SdfSpatialExtentsAggregateReader \
class, it takes the extents from its spatial index. If your data store has the \
extents precomputed like this, you can use the SpatialExtents property in your FDO \
Provider to get this information to the FDO client (Map or MapGuide). The clients \
are already coded to look for the SpatialExtents property.
Gavin
-----Original Message-----
From: fdo-users-bounces@lists.osgeo.org [mailto:fdo-users-bounces@lists.osgeo.org] On \
Behalf Of Greg Boone
Sent: Wednesday, February 20, 2008 3:10 PM
To: FDO Users Mail List
Subject: RE: [fdo-users] view scale
Hi Artem,
I think is some general confusion regarding your request for information. Can you \
reformulate your request providing use case/workflow information specific to your \
business case? Maybe this will help generate the specific information that you \
request.
Regards,
Greg
-----Original Message-----
From: fdo-users-bounces@lists.osgeo.org [mailto:fdo-users-bounces@lists.osgeo.org] On \
Behalf Of Artyom
Sent: Wednesday, February 20, 2008 11:47 AM
To: fdo-users@lists.osgeo.org
Subject: RE: [fdo-users] view scale
Can you give some concrete instructions please.
Artem
Gavin Cramer wrote:
>
> Normally, one would use the SpatialExtents computed property from a
> SelectAggregates command. This property, along with Count(), is supported
> by many providers, often with an optimized implementation where possible.
>
> Since you are implementing a provider yourself, that would be the place to
> implement any means that you can find to get the actual extents of stored
> features. This is as opposed to the extents of a Spatial Context, which
> are typically set as the largest reasonable extent possible for the
> context.
>
> When an optimized means is not available, the usual last resort is a
> retrieval of all features in the layer. If you can efficiently get them
> into FGF format, FdoSpatialUtility::GetExtents is the fastest means to
> compute the extent of each feature.
>
> Gavin
>
>
> -----Original Message-----
> From: fdo-users-bounces@lists.osgeo.org
> [mailto:fdo-users-bounces@lists.osgeo.org] On Behalf Of Artyom
> Sent: Tuesday, February 19, 2008 11:47 AM
> To: fdo-users@lists.osgeo.org
> Subject: RE: [fdo-users] view scale
>
>
> My provider must be for both types.
>
> If it is possible to give me an information about how to get it for
> features?
>
> Thank you
>
>
> Traian Stanev wrote:
> >
> >
> > You cannot get the screen extent from inside an FDO provider, unless your
> > data is raster. Is your data raster?
> >
> >
> > If your data is vectors, you could add a custom function that can be used
> > with a Select command to pass such arguments (like raster providers do),
> > however, you would need to ensure that FDO clients like Map and MapGuide
> > in turn use this custom function when requesting data from your provider.
> >
> >
> > Traian
> >
> >
> >
> > > -----Original Message-----
> > > From: fdo-users-bounces@lists.osgeo.org [mailto:fdo-users-
> > > bounces@lists.osgeo.org] On Behalf Of Artyom
> > > Sent: Monday, February 18, 2008 11:40 AM
> > > To: fdo-users@lists.osgeo.org
> > > Subject: RE: [fdo-users] view scale
> > >
> > >
> > > Hi again
> > >
> > > It seems that I gave not enough information about what I need.
> > >
> > > As mentioned Orest I need the scale such as e.g. 1:20,000. To compute
> > > it I
> > > need a full extent of my data, and a current extent of the view. There
> > > is a
> > > method FdoSpatialUtility::GetExtents wich fills an extend using a
> > > FdoSpatialCondition. But it is an incorrect method as I understand it
> > > does
> > > not return an extend of the current "View". To use formula given by
> > > Orest
> > >
> > > Scale = sqrt((dbmaxy-dbminy)**2 + (dbmaxx-dbminx)**2) /
> > > sqrt((scrmaxy-scrminy)**2 + (scrmaxx-scrminx)**2)
> > >
> > > I need a screen extent. How can I get it.
> > >
> > > Thanks
> > >
> > >
> > > Orest Halustchak wrote:
> > > >
> > > > Hi Artyom,
> > > >
> > > > Just to clarify, what scale do you need to find? By "view scale" do
> > > you
> > > > mean the scale between a map display and ground coordinates (e.g.
> > > > 1:20,000)? If that's really what you mean, then FDO itself has
> > > nothing to
> > > > do with that scale. FDO is independent of any map display. Scale
> > > would
> > > > have to be computed outside of FDO.
> > > >
> > > > Thanks,
> > > > Orest.
> > > >
> > > > -----Original Message-----
> > > > From: fdo-users-bounces@lists.osgeo.org
> > > > [mailto:fdo-users-bounces@lists.osgeo.org] On Behalf Of Artyom
> > > > Sent: Friday, February 15, 2008 9:36 AM
> > > > To: fdo-users@lists.osgeo.org
> > > > Subject: RE: [fdo-users] view scale
> > > >
> > > >
> > > > Our data type does not have a measure information. We have type of
> > > objects
> > > > that contains some attributive information but mostly it xyz. And to
> > > read
> > > > our data not enough to know only current extent.
> > > > About the coordination system can't say anything concrete for now.
> > > Because
> > > > I
> > > > need to convert our coordininate system to WKT. now I use only
> > > default
> > > > system. I'll research this question a bit later. And by the way my
> > > > provider
> > > > is unmanaged. I couldn't find the entry point for managet connection
> > > wich
> > > > could be equivalent to the unmanaged FdoIConnection* CreateConnection
> > > ().
> > > > So
> > > > if there is any way to find the scale not using the measure value? Or
> > > it
> > > > can
> > > > be done by FDO spatial utilities?
> > > >
> > > > Thank you for you replies!
> > > >
> > > >
> > > >
> > > > Orest Halustchak wrote:
> > > > >
> > > > > Hi,
> > > > >
> > > > > Artyom, FDO itself deals with data access and has nothing to do with
> > > view
> > > > > scales or other view / rendering attributes. That's up to client
> > > > > applications such as MapGuide. The data itself is stored in units
> > > defined
> > > > > by the CRS as Maksim points out. Even M (measure) values that might
> > > be
> > > > > stored are not tied to any view or view scale. They often are based
> > > on
> > > > > ground distance, but can be other units as an application may
> > > define.
> > > > >
> > > > > Thanks,
> > > > > Orest.
> > > > >
> > > > > -----Original Message-----
> > > > > From: fdo-users-bounces@lists.osgeo.org
> > > > > [mailto:fdo-users-bounces@lists.osgeo.org] On Behalf Of Maksim
> > > Sestic
> > > > > Sent: Friday, February 15, 2008 5:24 AM
> > > > > To: fdo-users@lists.osgeo.org
> > > > > Subject: RE: [fdo-users] view scale
> > > > >
> > > > >
> > > > > OSgeo::FDO::Geometry::DirectPositionImpl has M() property - it
> > > represents
> > > > > a
> > > > > Measure related to given coordinate. It's on you to implement
> > > parsing of
> > > > > the
> > > > > measure information and extracting something meaningful out of it.
> > > > > Geometry,
> > > > > as it is, doesn't posses a scale - it's unitless by default.
> > > > >
> > > > > On the other hand, FeatureStore may have CRS (Coordinate Reference
> > > > > System)
> > > > > set. CRS establishes soft spatial relation between the "space"
> > > > > (container)
> > > > > and geometric entities placed in it. It's definition does posses
> > > measure
> > > > > info, just look under UNITS part of CRS WKT string.
> > > > >
> > > > > Regards,
> > > > > Maksim Sestic
> > > > >
> > > > >
> > > > >
> > > > > Artyom wrote:
> > > > > >
> > > > > > I'm developing an Fdo provider. And I need scale, no metter if it
> > > is
> > > > > > MapGuide or AutoDesk Map 3D. Is it possible to get the scale by
> > > FDO? Or
> > > > > > my
> > > > > > problem has no solution?
> > > > > >
> > > > >
> > > > > --
> > > > > View this message in context:
> > > > > http://www.nabble.com/view-scale-tp15432859s18162p15497822.html
> > > > > Sent from the fdo-users mailing list archive at Nabble.com.
> > > > >
> > > > > _______________________________________________
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> > > > >
> > > >
> > > > --
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> > > >
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> > > --
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> > >
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> >
> >
>
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>
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