[Geoserver-users] Cartesian SRS

Hi everybody,
I use a WMS to explore aerial photos that are no rectified and that have
an approssimate georeferentiation.
To do this, I've spread the photos in a virtual 2D space (a cartesian
plane with origin in 0,0) by assigning them a calculated world file and
I've built a image catalog to load them into a map server (BTW it's
ArcIMS).
The application let the user choose the area of interest navigating in a
real GIS map and, once it has identified the photo that cover that area
using the point clicked by the user and the approssimate bounding box of
the photos, the photo is shown with thw WMS. When viewing the single
photo, the application restricts the user's zooms and pans to the extent
of the photo so not to reveal that he/she is navigating in this
fictitious space where are placed the photos.

Here is the question: I want to migrate the application to the Geoserver
WMS and I'm trying to define an image mosaic. I created the shape file
with gdaltindex, I wrote the .properties file but I don't know which
.prj file I can use. I'm tryng with a WKT with LOCAL_CS and Geoserver
rejects my image mosaic saying nothing but "Invalid url:
'file:coverages/fotocosta2/cata.shp' for format type:'ImageMosaic'". No
other info in the log.

Any hints?
Stefano

Stefano Pezzi
CORE Soluzioni Informatiche srl
                                  
stefano.pezzi@anonymised.com
http://www.corenet.it
Via Calzolerie, 2 - 40125
BOLOGNA
tel. +39.051.237823
fax. +39.051.270806
                                  

Stefano.Pezzi@anonymised.com ha scritto:

Hi everybody,
I use a WMS to explore aerial photos that are no rectified and that have
an approssimate georeferentiation.
To do this, I've spread the photos in a virtual 2D space (a cartesian
plane with origin in 0,0) by assigning them a calculated world file and
I've built a image catalog to load them into a map server (BTW it's
ArcIMS).
The application let the user choose the area of interest navigating in a
real GIS map and, once it has identified the photo that cover that area
using the point clicked by the user and the approssimate bounding box of
the photos, the photo is shown with thw WMS. When viewing the single
photo, the application restricts the user's zooms and pans to the extent
of the photo so not to reveal that he/she is navigating in this
fictitious space where are placed the photos.

Here is the question: I want to migrate the application to the Geoserver
WMS and I'm trying to define an image mosaic. I created the shape file
with gdaltindex, I wrote the .properties file but I don't know which
.prj file I can use. I'm tryng with a WKT with LOCAL_CS and Geoserver
rejects my image mosaic saying nothing but "Invalid url:
'file:coverages/fotocosta2/cata.shp' for format type:'ImageMosaic'". No
other info in the log.

Eh, interesting use case. Beware you're going into uncharted land, as far as I know nobody ever tried to work with data in a pure cartesian
space so far.

That said, the following WKT definition is parsed properly and should
give you what you're looking for:
LOCAL_CS["Cartesian Grid", LOCAL_DATUM["XY grid", 0], UNIT["m", 1.0], AXIS["x", EAST], AXIS["y", NORTH]]

You can also add it to the user projections so that you can use it
in the GeoServer UI as well.

Well, let me know how it goes, we probably need to add that to the
user interface as well, so that when a CS is unknown, we default
to a pure cartesian space.

Hmm... which prompts me for our resident CRS expert, Martin Desriusseaux. Martin, do you think it makes sense to create
a new epsg module serving two extra CRS, one that is a flat 2d CRS
that complains loudly when someone tries to convert it to another
CRS (un-transformable flat crs) and another does not complain and
simply stays the same, just like DefaultEngineeringCRS.CARTESIAN_2D
and DefaultEngineeringCRS.GENERIC_2D, respectively?

Cheers
Andrea

Note also that there was a Summer of Code project (presentation on it: http://www.foss4g2007.org/presentations/viewattachment.php?attachment_id=125) to add algorithms to transform rasters of unknown coordinate reference systems to real world coordinate systems. Jan can probably give you more information, it could be helpful to achieve what you're looking to do.

This could easily be used as the basis of something like http://labs.metacarta.com/rectifier/ - which is closed source, but uses a lot of open source components. It lets users put in more control points than just bounding box.

best regards,

Chris

Andrea Aime wrote:

Stefano.Pezzi@anonymised.com ha scritto:

Hi everybody,
I use a WMS to explore aerial photos that are no rectified and that have
an approssimate georeferentiation.
To do this, I've spread the photos in a virtual 2D space (a cartesian
plane with origin in 0,0) by assigning them a calculated world file and
I've built a image catalog to load them into a map server (BTW it's
ArcIMS).
The application let the user choose the area of interest navigating in a
real GIS map and, once it has identified the photo that cover that area
using the point clicked by the user and the approssimate bounding box of
the photos, the photo is shown with thw WMS. When viewing the single
photo, the application restricts the user's zooms and pans to the extent
of the photo so not to reveal that he/she is navigating in this
fictitious space where are placed the photos.

Here is the question: I want to migrate the application to the Geoserver
WMS and I'm trying to define an image mosaic. I created the shape file
with gdaltindex, I wrote the .properties file but I don't know which
.prj file I can use. I'm tryng with a WKT with LOCAL_CS and Geoserver
rejects my image mosaic saying nothing but "Invalid url:
'file:coverages/fotocosta2/cata.shp' for format type:'ImageMosaic'". No
other info in the log.

Eh, interesting use case. Beware you're going into uncharted land, as far as I know nobody ever tried to work with data in a pure cartesian
space so far.

That said, the following WKT definition is parsed properly and should
give you what you're looking for:
LOCAL_CS["Cartesian Grid", LOCAL_DATUM["XY grid", 0], UNIT["m", 1.0], AXIS["x", EAST], AXIS["y", NORTH]]

You can also add it to the user projections so that you can use it
in the GeoServer UI as well.

Well, let me know how it goes, we probably need to add that to the
user interface as well, so that when a CS is unknown, we default
to a pure cartesian space.

Hmm... which prompts me for our resident CRS expert, Martin Desriusseaux. Martin, do you think it makes sense to create
a new epsg module serving two extra CRS, one that is a flat 2d CRS
that complains loudly when someone tries to convert it to another
CRS (un-transformable flat crs) and another does not complain and
simply stays the same, just like DefaultEngineeringCRS.CARTESIAN_2D
and DefaultEngineeringCRS.GENERIC_2D, respectively?

Cheers
Andrea

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