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

[JonasBrunzell]

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

[MelitaKennedy]

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

[JonasBrunzell]

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

[MelitaKennedy]

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

[JonasBrunzell]

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

/Jonas

[MelitaKennedy]

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

[JonasBrunzell]

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

[JonasBrunzell]

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?

[MelitaKennedy]

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