[fdo-users] view scale

[Traian Stanev]

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 at lists.osgeo.org [mailto:fdo-users-
> bounces at lists.osgeo.org] On Behalf Of Artyom
> Sent: Monday, February 18, 2008 11:40 AM
> To: fdo-users at 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 at lists.osgeo.org
> > [mailto:fdo-users-bounces at lists.osgeo.org] On Behalf Of Artyom
> > Sent: Friday, February 15, 2008 9:36 AM
> > To: fdo-users at 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 at lists.osgeo.org
> >> [mailto:fdo-users-bounces at lists.osgeo.org] On Behalf Of Maksim
> Sestic
> >> Sent: Friday, February 15, 2008 5:24 AM
> >> To: fdo-users at 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?
> >>>
> >>
> >> --
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> >>
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> >>
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