Masking noise within DEM?

tim53tim53 Global Mapper UserPosts: 68Trusted User
edited May 2015 in Elevation Data
Hi:

I'm working with orthomosaics and DEMs from the Mars Opportunity and Curiosity rovers, and I'd like to be able to crop out areas where the stereo model has included parts of the rovers that were in the field of view when the panoramas were acquired, so they show up as "spikes" in the terrain. Since these are usually in the center of a 360 degree orthomosaic around the rover, I can't just create a polygon over the parts of the rover and "crop to polygon", as that would delete everything except what I'm trying to remove.

Is there a mask tool somewhere? For the image, I was able to create a black polygon feature over the parts of the rover and export a raster at the same resolution as the original orthomosaic that included the polygon feature, but the same did not work for the DEM, even when I selected the polygon layer and the DEM layer together for the export elevation grid.

-Tim.

Comments

  • MykleMykle Global Mapper User Posts: 442Trusted User
    edited May 2015
    Tim,

    Not knowing what file types you are working with, I simply used the Global Mapper Grid format for testing.

    Given a 10m DEM (not on Mars). Create an area feature (I used a square), then assign elevations to the vertices.
    (Select the area feature, on the right-click menu use Vertex Editing | Feature Vertex List, then select Add Elevs)
    Select your area feature and use Analysis | Create Elevation Grid from 3D Vector Data.

    Now you can hide all but your DEM and your "Triangulated Elevation Grid 1" (unless you named it differently), and export the grid. Load the new file, turn off the rest of the layers, and you should see a surface with the elevations set within your feature.

    I have not tried setting to a Not-An-Elevation value. So the rover spikes will be gone but it's up to you whether simply replacing the area will do what you need. Global Mapper doesn't have methods to edit elevations other than as
    vertices of vector features (AFAIK).

    It is also possible that other elevation formats may behave differently.

    I'd like to see an elevation grid over "Spirit of St. Louis" crater ;-)

    Mykle
  • tim53tim53 Global Mapper User Posts: 68Trusted User
    edited May 2015
    Mykle wrote: »
    Tim,

    Not knowing what file types you are working with, I simply used the Global Mapper Grid format for testing.

    For Curiosity, I'm using elevation grids that are 32-bit tiff files. For Opportunity, I'm making my own from the point cloud data (still dying to figure out how to make my own point clouds from stereo pairs from other projects).
    Given a 10m DEM (not on Mars). Create an area feature (I used a square), then assign elevations to the vertices.
    (Select the area feature, on the right-click menu use Vertex Editing | Feature Vertex List, then select Add Elevs)
    Select your area feature and use Analysis | Create Elevation Grid from 3D Vector Data.

    Now you can hide all but your DEM and your "Triangulated Elevation Grid 1" (unless you named it differently), and export the grid. Load the new file, turn off the rest of the layers, and you should see a surface with the elevations set within your feature.

    I have not tried setting to a Not-An-Elevation value. So the rover spikes will be gone but it's up to you whether simply replacing the area will do what you need. Global Mapper doesn't have methods to edit elevations other than as
    vertices of vector features (AFAIK).

    I'll try this. For the Mars rovers, I first use ArcMap to georeference the orthomosaic and DEM to the base map (orbiter images, 25cm/pixel), then I export the orthomosaic and DEM as rectified files for importing to Global Mapper, where I adjust the height of the rover's DEM to match the orbiter-based DEM's elevation. When I export from Arcmap, I set "no data" to 0, so I don't have to do a separate background transparency step. I don't know if the "0" from Arcmap is equivalent to a DN value of 0 in the DEM, but it works.
    It is also possible that other elevation formats may behave differently.

    I'd like to see an elevation grid over "Spirit of St. Louis" crater ;-)

    Mykle

    Well, it's not Spirit of Saint Louis, but here's a not so long ago view from Curiosity. This sample shows the "spikes" from rover parts in the mosaic.

    Sample_3D_perspective.jpg
  • MykleMykle Global Mapper User Posts: 442Trusted User
    edited May 2015
    Very nice! Now if only the surface traction could be estimated. Soft sand is better for the wheels, as long as they don't get stuck (again). Hopefully the roughest rocks have been left behind.
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