Creating Elevation Grid from DXF for Creating 3D Faces
BrianZ111
Global Mapper UserTrusted User
Hi, I have some DXF files and I'm not super familiar with the format, but my understanding is the format I have is just points and lines and I need to generate 3D faces for them.
DXF_Polygons.jpg
When I try to create an elevation grid from the DXF in Global Mapper for this purpose I get a mess of polygons and sharp edges along lines where I do not expect them.
DXF_No_Faces.jpg
I can turn this DXF into a DAE, load it into MeshLab and use the Qhull library though Filters > Point Set > Select Visible Points to generate the faces and save it back out as DXF. This gets much better results which you can see if you load the DXF saved out of MeshLab into Global Mapper and grid it. The polygons are the same as before so I assume Global Mapper is just using the now existing 3D faces when gridding.
DXF_With_MeshLab_Generated_Faces.jpg
Global Mapper and this MeshLab filter get pretty much the same results when I run LiDAR through them, which is just points. Why do I see such different results for these DXF files that are points and lines? I'd like to be able to just generate it through Global Mapper if possible as the MeshLab way requires extra steps and takes forever to generate, plus I still have to bring it into Global Mapper to rectify and crop imagery. Are there certain settings I can set different or is Global Mapper just not designed to handle this kind of task? Sorry if I'm misunderstanding something simple here.
Thanks for any help.
DXF_Polygons.jpg
When I try to create an elevation grid from the DXF in Global Mapper for this purpose I get a mess of polygons and sharp edges along lines where I do not expect them.
DXF_No_Faces.jpg
I can turn this DXF into a DAE, load it into MeshLab and use the Qhull library though Filters > Point Set > Select Visible Points to generate the faces and save it back out as DXF. This gets much better results which you can see if you load the DXF saved out of MeshLab into Global Mapper and grid it. The polygons are the same as before so I assume Global Mapper is just using the now existing 3D faces when gridding.
DXF_With_MeshLab_Generated_Faces.jpg
Global Mapper and this MeshLab filter get pretty much the same results when I run LiDAR through them, which is just points. Why do I see such different results for these DXF files that are points and lines? I'd like to be able to just generate it through Global Mapper if possible as the MeshLab way requires extra steps and takes forever to generate, plus I still have to bring it into Global Mapper to rectify and crop imagery. Are there certain settings I can set different or is Global Mapper just not designed to handle this kind of task? Sorry if I'm misunderstanding something simple here.
Thanks for any help.
Comments
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What version of Global Mapper are you using? In more recent versions if you grid a TIN it should directly sample each TIN face, so any edges are present in the TIN surface itself. Likely they are minor edges, but accentuated by the hill shading.
You might try gridding the TIN surface with the option to use edges as constraints unchecked so that just the 3D points at each TIN corner are used and the areas themselves ignored.
Thanks,
Mike
Global Mapper Guru
geohelp@bluemarblegeo.com
Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation -
Thanks, I had some build of 15.1 in those screenshots. After I posted last night I downloaded from here: http://www.bluemarblegeo.com/downloads/global-mapper/global_mapper15_64bit.zip and dropped the contents in my install location to be sure I had the latest, it says (b042214) now. It didn't help any though, it still looks pretty much the same. I actually already had the edges as constraints option unchecked. With it checked it actually looks a little better but still not acceptable for my purposes.
DXF_Edges_Constraints_Checked.jpg
This is ultimately being used as a model of terrain for a golf course in a simulator so it needs to be fairly smooth and accurate at a fairly high resolution. In addition to the pronounced polygon look, the elevations just seem to be wrong in places. For example the middle part of this green is collapsed down compared to file after faces are generated in MeshLab.
17_Green_Global_Mapper_vs_MeshLab.jpg -
If you manually specify a grid spacing and make it smaller how does it look? It could be that the automatically selected grid spacing is too large.
If that doesn't help, can you provide the DXF so that I can give it a try?
Thanks,
Mike
Global Mapper Guru
geohelp@bluemarblegeo.com
Global Mapper -
It looks the same setting it lower. Here's the file I was using in the screenshots: http://www.zagerdesign.com/temp/becc_dxf.zip The section I was posting images from is a little northwest of center. Not sure if the projection matters but I'm using Orthographic and approximate coordinates (-89.87, 44.36) as I have my own imagery to rectify to it anyway. The planar and elevation units are in feet. If you want I can also post the output file after running it through MeshLab. Thanks for taking a look at it.
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Thanks for the file, I found the problem. The DXF file didn't set the 3D flag for the POLYLINE entities, so Global Mapper was just treating each area as a 2D area with a single elevation rather than using the elevation for each vertex. I've updated the importer to use the elevation for each vertex even if the file didn't set the flags properly, which should fix the stepped appearance. I have placed a new build at http://www.bluemarblegeo.com/downloads/global-mapper/global_mapper15.zip with the latest changes for you to try. Simply download that file and extract the contents into your existing v15.xx installation folder to give it a try. If you are using the 64-bit v15 version there is a new build at http://www.bluemarblegeo.com/downloads/global-mapper/global_mapper15_64bit.zip .
Thanks,
Mike
Global Mapper Guru
geohelp@bluemarblegeo.com
Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation -
Yes that did it! Thank you very much. You've saved me a lot of time.
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