topic Re: Can't change raster file reference system from Sweref 99 13 30 to Sweref 99 TM in Data Management Questions

Can't change raster file reference system from Sweref 99 13 30 to Sweref 99 TM

JonasBrunzell — Sun, 05 Feb 2012 20:45:51 GMT

Hello,

When I try to project two different height models (rasters) upon each other, the two rasters do not align properly. It is a difference of around 5 meters between them. The first raster is in Sweref 99 TM, the other one I have tried to reproject into Sweref 99 TM from Sweref 99 13 30, using the tool Reproject Raster in ArcToolbox. I have also tried it the other way around. I get the same result whatever I do.

Does anyone know a possible reason why the files are not projected correctly together, even though I have changed the reference system of one of them to fit the other?

Please help!Many thanks,
Jonas

Re: Can't change raster file reference system from Sweref 99 13 30 to Sweref 99 TM

MelitaKennedy — Mon, 06 Feb 2012 00:32:12 GMT

Hi Jonas,

Is the 5m offset in the XY values or in the Z values? The project raster tool will not affect any vertical values at this time. If it's 5m in XY, what are the cell sizes of the two rasters?

Melita

Re: Can't change raster file reference system from Sweref 99 13 30 to Sweref 99 TM

JonasBrunzell — Mon, 06 Feb 2012 10:03:30 GMT

Thanks for answering. The difference is in XY. The cellsize of both rasters is 2m.

Re: Can't change raster file reference system from Sweref 99 13 30 to Sweref 99 TM

MelitaKennedy — Mon, 06 Feb 2012 20:52:11 GMT

Hmm, there's no datum transformation, and both use close central meridian values (13 30 versus 15), so I wouldn't expect that to be a problem. Because they're rasters, you might want to try setting a registration point in the Project Raster tool. Because you're trying to match a target raster, I would use its lower left corner as the registration point. The raster that you're projecting does not need to actually include that point.

Melita

Re: Can't change raster file reference system from Sweref 99 13 30 to Sweref 99 TM

JonasBrunzell — Thu, 09 Feb 2012 14:32:50 GMT

Thanks for the ideas, I will try that. Could there still be something wrong with the transformation formulas, do you think?

/Jonas

Re: Can't change raster file reference system from Sweref 99 13 30 to Sweref 99 TM

MelitaKennedy — Thu, 09 Feb 2012 17:19:03 GMT

Hi Jonas,

Honestly, I doubt it. The map projection is transverse Mercator which is widely used for UTM and in the US for state plane zones. If there was something wrong in the algorithm, I think we would have found it, and a problem would likely lead to offsets more than 5m.

Melita

Re: Can't change raster file reference system from Sweref 99 13 30 to Sweref 99 TM

JonasBrunzell — Thu, 09 Feb 2012 19:28:14 GMT

That is good to know, then I will look for other causes of my problem!

Re: Can't change raster file reference system from Sweref 99 13 30 to Sweref 99 TM

JonasBrunzell — Sat, 18 Feb 2012 09:28:59 GMT

Hello again,

I may perhaps have lied earlier, cause when I read the information about the rasters under Properties, I see that one of them has the following info:

Spatial reference: GRS_1980_Transverse_Mercator
Datum: D_GRS_1980
Central Meridian: 13,5
Scale Factor: 1

The other one has this info:

Spatial reference: UTM
Datum: SWEREF99
Central Meridian: 15
Scale Factor: 0,9996

The first raster is supposed to be in the system Sweref 99 1330 and the second one in Sweref 99 TM (according to what I've been told). Does the information above suggest something else?

Could it be, that there is a datum transformation taking place when I project the rasters upon each other, and in that case, could such a transformation possibly cause the 5 m mismatch?

Re: Can't change raster file reference system from Sweref 99 13 30 to Sweref 99 TM

MelitaKennedy — Sat, 18 Feb 2012 20:59:18 GMT

It's possible, but it would have to be a custom transformation. We don't have any that use a GRS 1980 datum. You might try defining the 13 30 raster with the Esri version (use Define Projection tool) and see if that clears up the 5m offset.

Melita