Import non projected data (mesh or heightfield)

TibTib Global Mapper UserPosts: 9
edited August 2012 in Projection Questions
Hello,

I'm trying to compare a mesh's elevation data (OBJ file) with DEM data (BIL file).

First I create a heightfield from the mesh by sampling the mesh's height values regularly along a 2D grid (in my application I cast vertical rays from above the mesh).

This gives me a heightfield which is not projected, for example a 60m x 60m regular grid of height values.

What I'd like to do is:

- Geoposition this heightfield (center it at a specified lat/lon)
- Compare it with a real DEM (BIL file in geographic coordinates)

But my problem is that, as my heightfield is not projected, it doesn't contain the distortions that the real DEM has.

I'm new to the world of projections but I'd like to know if it's possible to:

- import a "not projected regular grid" as DEM data (by specifying geoposition) and convert it to geographic coordinates

- or to consider that this heightfield is already projected (I saw some projections have planar units in meter like Lambert conformal conic for example) and then convert the projection in geographic coordinates.

- directly import the original mesh in GM by specifying geoposition


The last way I see is, in my application, to generate the heightfield with distortion by positioning the mesh on the earth (with good geoposition) and casting rays in the direction of the earth's center to sample elevation data but I hope there is a simpler way in Global Mapper...

I hope I made my problem easy to understand...

Thank you!

Thibaud

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited August 2012
    Thibaud,

    If you have your regular grid and can load it into Global Mapper, just pick some fake projection (like Geographic), then once you have it and the actual DEM loaded, right-click on your heightfield in the Control Center and select to Reposition it. You can then provide control points to rectify your grid against the real DEM to get them lined up in real space. You can then use File->Combine Terrains if you want to do a mathematical subtraction of the surfaces.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • TibTib Global Mapper User Posts: 9
    edited August 2012
    Hello Mike,

    Thanks for the answer.

    I'm not sure to understand,

    What you tell me is to import the regular grid with some random projection and then to manually rectify the grid.

    But the problem is that I have no reference to rectify the grid. The grid is generated upon a 3D mesh so I have no real DEM that I can use to have the points line up in real space. (the DEM that I want to compare and the mesh are two independant data).

    It's like I had only a regular grid with no projection that I would like to geoposition and project (to get the distortion).

    Thank you,

    Thibaud
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited August 2012
    Thibaud,

    Oh I had assumed that they were of the same area. Are the corners supposed to be the same or anything like that or do you at least know the corner coordinates of your 3D mesh in lat/lon? If so you could add control points for the corners to get it positioned on the earth.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
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