[Geoserver-users] Pre-generalized datastore

Matthias_Muller · October 25, 2011, 3:02pm

Hi,

does anybody have experience with the pregeneralized datastore? I would really like to try this one a larger dataset which contains complex polygons in WGS84.
The critical parameter for this module is the "generalisation distance". - But what is the unit for that distance? Is it in dataset units (degrees in the case of WGS84 source) or is it in meters?

Thanks,
Matthias

Christian_Mueller · October 25, 2011, 3:16pm

Hi, I am the developer. The distance unit is taken from the coordinate system. Decimal degrees for wgs84.

What is your backend store, I hope you are not working with shape files.
Here is a postgis tutorial, until now I had not the time to write an official one. This tutorial can be adapted to other databases as well.

Cheers
Christian

Zitat von Matthias Müller <Matthias_Mueller@anonymised.com>:

Hi,

does anybody have experience with the pregeneralized datastore? I would
really like to try this one a larger dataset which contains complex
polygons in WGS84.
The critical parameter for this module is the "generalisation
distance". - But what is the unit for that distance? Is it in dataset
units (degrees in the case of WGS84 source) or is it in meters?

Thanks,
Matthias

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Matthias_Muller · October 25, 2011, 4:24pm

Hi Christian,

thanks for the hint and appreciation for your work. I am planning to use this module on a PostGIS Datastore - if you have a documentation I'd really like to read it. Right now I am diving into the subtleties of feature generalization.
Decimal degrees are a bit tricky as the "real" generalisation distances increase towards the equator. The choice is to either get too much detail when reqesting data at medium or high latitudes or loose detail around the equator. (I'll first try the conservative choice and check the response times).

Cheers,
Matthias

Am 25.10.2011 17:16, schrieb christian.mueller@anonymised.com:

Hi, I am the developer. The distance unit is taken from the coordinate
system. Decimal degrees for wgs84.

What is your backend store, I hope you are not working with shape files.
Here is a postgis tutorial, until now I had not the time to write an
official one. This tutorial can be adapted to other databases as well.

Cheers
Christian

Zitat von Matthias Müller<Matthias_Mueller@anonymised.com>:

Hi,

does anybody have experience with the pregeneralized datastore? I would
really like to try this one a larger dataset which contains complex
polygons in WGS84.
The critical parameter for this module is the "generalisation
distance". - But what is the unit for that distance? Is it in dataset
units (degrees in the case of WGS84 source) or is it in meters?

Thanks,
Matthias

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Christian_Mueller · October 26, 2011, 12:10am

Forgot the link to the tutorial
http://osgeo-org.1803224.n2.nabble.com/attachment/6137141/0/pregen_tutorial.html

Zitat von Matthias Müller <Matthias_Mueller@anonymised.com>:

Hi Christian,

thanks for the hint and appreciation for your work. I am planning to
use this module on a PostGIS Datastore - if you have a documentation
I'd really like to read it. Right now I am diving into the subtleties
of feature generalization.
Decimal degrees are a bit tricky as the "real" generalisation distances
increase towards the equator. The choice is to either get too much
detail when reqesting data at medium or high latitudes or loose detail
around the equator. (I'll first try the conservative choice and check
the response times).

The module chooses the generalization level for itself at runtime. The idea is not to draw a pixel multiple times for a given pixel dimension (WMS request as an example). The amount of net traffic is reduced and you have less memory and cpu consumption.

Cheers,
Matthias

Am 25.10.2011 17:16, schrieb christian.mueller@anonymised.com:

Hi, I am the developer. The distance unit is taken from the coordinate
system. Decimal degrees for wgs84.

What is your backend store, I hope you are not working with shape files.
Here is a postgis tutorial, until now I had not the time to write an
official one. This tutorial can be adapted to other databases as well.

Cheers
Christian

Zitat von Matthias Müller<Matthias_Mueller@anonymised.com>:

Hi,

does anybody have experience with the pregeneralized datastore? I would
really like to try this one a larger dataset which contains complex
polygons in WGS84.
The critical parameter for this module is the "generalisation
distance". - But what is the unit for that distance? Is it in dataset
units (degrees in the case of WGS84 source) or is it in meters?

Thanks,
Matthias

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demand for specialized networking skills is growing even more rapidly.
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http://p.sf.net/sfu/cisco-dev2dev
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Matthias_Muller · October 26, 2011, 4:21pm

Looks good, this is what I need for a quick start; thank you!

One more question: If you issue a getFeatureInfo Request to Geoserver - what does the pregeneralized module do? Will it read the Attribute Information a generalized dataset or will it use the original one? I am asking because a custom generalisation process might merge features an thus discard the original attributes.

Cheers,
Matthias

Am 26.10.2011 02:10, schrieb christian.mueller@anonymised.com:

Forgot the link to the tutorial
http://osgeo-org.1803224.n2.nabble.com/attachment/6137141/0/pregen_tutorial.html

Zitat von Matthias Müller <Matthias_Mueller@anonymised.com>:

Hi Christian,

thanks for the hint and appreciation for your work. I am planning to
use this module on a PostGIS Datastore - if you have a documentation
I'd really like to read it. Right now I am diving into the subtleties
of feature generalization.
Decimal degrees are a bit tricky as the "real" generalisation distances
increase towards the equator. The choice is to either get too much
detail when reqesting data at medium or high latitudes or loose detail
around the equator. (I'll first try the conservative choice and check
the response times).

The module chooses the generalization level for itself at runtime. The
idea is not to draw a pixel multiple times for a given pixel dimension
(WMS request as an example). The amount of net traffic is reduced and
you have less memory and cpu consumption.

Cheers,
Matthias

Am 25.10.2011 17:16, schrieb christian.mueller@anonymised.com:

Hi, I am the developer. The distance unit is taken from the coordinate
system. Decimal degrees for wgs84.

What is your backend store, I hope you are not working with shape files.
Here is a postgis tutorial, until now I had not the time to write an
official one. This tutorial can be adapted to other databases as well.

Cheers
Christian

Zitat von Matthias Müller<Matthias_Mueller@anonymised.com>:

Hi,

does anybody have experience with the pregeneralized datastore? I would
really like to try this one a larger dataset which contains complex
polygons in WGS84.
The critical parameter for this module is the "generalisation
distance". - But what is the unit for that distance? Is it in dataset
units (degrees in the case of WGS84 source) or is it in meters?

Thanks,
Matthias

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demand for specialized networking skills is growing even more rapidly.
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Christian_Mueller · October 27, 2011, 1:53am

Interesting question. The plugin switches between generalizations if it gets a special hint from the rendering component. The value of the hint is the pixel size in world coordinates.

AFAIK, the getFeatureInfo will not pass this hint to the pregen feture store (does not make sense). Without the hint, the original geometry is used.

Independent of the geometry chosen, you will always get ALL attributes. As an example, if one uses shape files (not recommended), you need a shape file for each generalization. A shape file can store exactly one geometry column and you have to duplicate all other attributes for each generalization. Nasty.

Hope this helps
Christin

Zitat von Matthias Müller <Matthias_Mueller@anonymised.com>:

Looks good, this is what I need for a quick start; thank you!

One more question: If you issue a getFeatureInfo Request to Geoserver -
what does the pregeneralized module do? Will it read the Attribute
Information a generalized dataset or will it use the original one? I am
asking because a custom generalisation process might merge features an
thus discard the original attributes.

Cheers,
Matthias

Am 26.10.2011 02:10, schrieb christian.mueller@anonymised.com:

Forgot the link to the tutorial
http://osgeo-org.1803224.n2.nabble.com/attachment/6137141/0/pregen_tutorial.html

Zitat von Matthias Müller <Matthias_Mueller@anonymised.com>:

Hi Christian,

thanks for the hint and appreciation for your work. I am planning to
use this module on a PostGIS Datastore - if you have a documentation
I'd really like to read it. Right now I am diving into the subtleties
of feature generalization.
Decimal degrees are a bit tricky as the "real" generalisation distances
increase towards the equator. The choice is to either get too much
detail when reqesting data at medium or high latitudes or loose detail
around the equator. (I'll first try the conservative choice and check
the response times).

The module chooses the generalization level for itself at runtime. The
idea is not to draw a pixel multiple times for a given pixel dimension
(WMS request as an example). The amount of net traffic is reduced and
you have less memory and cpu consumption.

Cheers,
Matthias

Am 25.10.2011 17:16, schrieb christian.mueller@anonymised.com:

Hi, I am the developer. The distance unit is taken from the coordinate
system. Decimal degrees for wgs84.

What is your backend store, I hope you are not working with shape files.
Here is a postgis tutorial, until now I had not the time to write an
official one. This tutorial can be adapted to other databases as well.

Cheers
Christian

Zitat von Matthias Müller<Matthias_Mueller@anonymised.com>:

Hi,

does anybody have experience with the pregeneralized datastore? I would
really like to try this one a larger dataset which contains complex
polygons in WGS84.
The critical parameter for this module is the "generalisation
distance". - But what is the unit for that distance? Is it in dataset
units (degrees in the case of WGS84 source) or is it in meters?

Thanks,
Matthias

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The demand for IT networking professionals continues to grow, and the
demand for specialized networking skills is growing even more rapidly.
Take a complimentary Learning@anonymised.com Self-Assessment and learn
about Cisco certifications, training, and career opportunities.
http://p.sf.net/sfu/cisco-dev2dev
_______________________________________________
Geoserver-users mailing list
Geoserver-users@lists.sourceforge.net
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