[fdo-users] view scale

Gavin Cramer gavin.cramer at autodesk.com
Wed Feb 20 15:29:05 EST 2008 

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 at lists.osgeo.org [mailto:fdo-users-bounces at 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 at lists.osgeo.org [mailto:fdo-users-bounces at lists.osgeo.org] On Behalf Of Artyom
Sent: Wednesday, February 20, 2008 11:47 AM
To: fdo-users at 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 at lists.osgeo.org
> [mailto:fdo-users-bounces at lists.osgeo.org] On Behalf Of Artyom
> Sent: Tuesday, February 19, 2008 11:47 AM
> To: fdo-users at 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 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?
>>> >>>
>>> >>
>>> >> --
>>> >> View this message in context:
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>>> >>
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>>> >>
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>
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