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Joined: Nov 2013
Posts: 70
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Posted: 18 Feb 2020, 13:07 

Hi

I found a weird behavior with Malt when providing an initial DEM.

With Malt Ortho, the Y <ResolutionPlani> sign has to be negative like any Geotags in GIS systems, while when using GeomImage strategy, I have to reverse the sign (being positive) in the XML of the DEM init. This is unexpected and to me, looks like a bug.





Antoine


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Joined: Jul 2011
Posts: 1050
Gender: Male
Age: 31
Posted: 19 Feb 2020, 13:24 

Hei,

In GeomImage, everything is in image coordinate, so +1 in the Y direction is always +1.

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Joined: Nov 2013
Posts: 70
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Posted: 19 Feb 2020, 13:54 

Hey,

thanks.

Yes I am well aware of the coordinate conventions but from the end user point of view, this should be adjusted on the fly by the GeomImage strategy and not adjusted by the user. Similarly, you do not adjust the GCP coordinates when dealing in GeomImage as opposed to the ortho/urbanMNE strategies; so this should be the same for the init DEM, since it is expressed in ground coordinates and not in image's coordinates (which wouldn't make sense at all as each image comes with its own orientation, so only common/absolute reference frame being the ground).

So now, me feeling is that GeomImage, even with a + in Y-direction wouldn't be able to consider properly the init DEM if this parameters has to be reversed. Again, the DEM init cannot be expressed in image geometry, it does not make any sense. or maybe I miss the usage of the DEM init in Malt. By the way, I noted little to none difference when I provide any DEM as init. I tried in shadowed, in steep terrains, I get the exact same results either I provide a DEM (with a resolution close to the one I've been requested to Malt). Is this really used ? I haven't looked into the source code yet.

Thanks


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Joined: Jul 2011
Posts: 1050
Gender: Male
Age: 31
Posted: 20 Feb 2020, 15:00 

Hei,

In Geomimage, there's never any DEM, it's a depth map that is created, from the Master image perspective. If you input an init DEM to it, it would at best confuse the hell out of MicMac, if you do have a depth map compatible with the geometry of the master image, then I guess why not, and I'm sure there's some reasonable cases where that would make sense.

The input DEM works, and works best (only) if the ZoomI is set pretty low (like 8), otherwise, the search band for the elevation is so large that it doesn't help. Giving an input DEM let's you skip the low resolution steps in the pyramid by initializing the elevation already pretty close to the end target.

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