Orthophotos in ECW with unsupported coordinate system

Re: Orthophotos in ECW with unsupported coordinate system

Mathieu St-pierre — Wed, 27 Oct 2010 00:53:19 GMT

Hi Erik,

Unfortunately there is no way to specify a special WKT string which would specify to use some coordinate system in the Bentley Geographic Coordinate System Library.

I sent you a email this morning (GMT -5) about the problem and refer you to Alain Robert, which might find some solution for you.

HTH,

Mathieu

Re: Orthophotos in ECW with unsupported coordinate system

wirring — Tue, 26 Oct 2010 16:44:38 GMT

Hi Mathieu

As far as I can find on the Net, the specification S34SRX is the correct GDAL specification for the Danish coordinate system "System 34 zone Sjælland". Since this is not a common projection how do I specify in ecw_cs.wkt that PowerMap (MicroStation) shall use "DanishS34-S99" from Bentley Geographic Coordinate System Library ??

Thanks,

Erik Wirring

Re: Orthophotos in ECW with unsupported coordinate system

Mathieu St-pierre — Thu, 21 Oct 2010 03:03:13 GMT

Hi Erik,

Ok, now I understand what is going on.

ECW files, which was created by ErMapper, have their own way of storing the geographic coordinate system in their file, which includes a coordinate system name, a datum name and a unit name.

When you attach a ECW file in Raster Manager it converts the geographic coordinate system in the ECW file to the MicroStation's internal geographic coordinate system representation.

The GDAL library is used for such conversion. In your MicroStation install path there is a file called \MicroStation\GeoCoordinateData\Gdal_Data\ecw_cs.wkt which contains the detailed information for each ECW geographic coordinate system name.

If you open that file you'll see that for the S34SRX coordinate system name the WKT is LOCAL_CS["S34SRX - (unsupported)"]. This is where the name S34SRX - (unsupported) comes from.

If you modify that file and add the correct WKT for S34SRX your problem should be solved.

As for why adding a new coordinate system doesn't modify that file is another question. I'll discuss about with some of my collegues.

Thanks,

Mathieu

Re: Orthophotos in ECW with unsupported coordinate system

wirring — Wed, 20 Oct 2010 11:48:56 GMT

Hi Mathieu,

That was exactly was i tried -with no luck!

"I have tried to copy the S34S coordinate system in the Coordinatesystem manager with the new name S34SRX --but that does not change a thing."

S34S is exactly the same as S34SRX, why the ECW file call it S34SRX I have no explanation for.

From the decription you can se that S34S and S34SRX are the same.

If I under Coordinate system select either S34S or S34RX the ECW file is reprojected correctly.

So why is the coordinate system marked as unsuported ??

Thanks in Advance

Erik Wirring

Re: Orthophotos in ECW with unsupported coordinate system

Mathieu St-pierre — Wed, 20 Oct 2010 01:32:37 GMT

Hi Erik,

If you want to reproject the ECW from S34S to a new coordinate system you must first ensure that the both the source coordinate system (S34S) and the destination coordinate system are defined in MicroStation geographic coordinate system database.

As Alain Robert told you a while ago there is tool available in PowerMap to define new coordinate system. Once both coordinate systems are available you can reproject on-the-fly the raster or, if you have Descartes, do what we call a physical reprojection, which is essentially a Save As operation but for which the coordinate system of the destination file is specified as Save As options.

Thanks,

Mathieu