Exporting a DTM (TIN) to ASCII Gid Format (ESRI - ArcGIS)

[Paul_Ollett]

Hi there,

Is it possible to export a DTM (TIN surface) to ESRI's ASCII grid format (for ArcGIS)?

I've attached an example file.

Failing that, is it possible to export to a simple XYZ point file?

Cheers,

Paul.

[neilyj666]

I'm not sure if this is possible - hopefully someone else will come in and prove me wrong...!!!

It is easy anough to produce a simple XYZ of the triangle points although the surface may not be exactly the same as the triangles are not exported.

Display the surface with points turned on and then Extract Objects > Points from the surface, then perform a data extraction or _MAPEXPORT on the Points direct to shp file (I've attached the dbf for one I just did)

[antoniovinci]

If you already added your TIN to a surface definition, then create a Dem file with _SURFACEEXPORTTODEM, finally you convert the resulting .TIF (or .DEM) to .ASC format, by means of the opensource Microdem.

[ksorsby]

Forgive me for resurrecting an old thread - is there still no direct way in 2014 to export a surface as an asc file from Civil 3D? I can't seem to find one.

Thanks,

Kevin

[rkmcswain]

I'll have to double check this with my GIS people, but I've been giving them LandXML files for a while with no complaints.

[ksorsby]

Thanks! I also don't have any issues with LandXML but I specifically need asc format files as that's what the flood modeller here requires.

Kevin

[Neilw_05]

I've found the Export to DEM tool is defective so it likely will not give satisfactory results. It may depend on your dataset however. Just be prepared to spend some time troubleshooting if you find the exported DEM is limited to a narrow band of data.

[Neilw_05]

You can't import a LandXML surface into basic ArcGIS. Perhaps they have an extension or a more robust application.

[ksorsby]

That's why I need to export the surfaces as an asc file. You can import them fairly well, but I need to export them.
We don't use ArcGIS, just Mapinfo and QGIS.

[TerryDotson]

... no direct way in 2014 to export a surface as an asc file from Civil 3D.

Keep in mind that assuming your surface is likely TIN based it will have to be converted to a grid first (since the ESRI Ascii Grid Format is grid based).  So regardless you are going to end up with a grid interpretation of your TIN.

ESRI has a TIN format, I think its called "ArcInfo UnGenTIN (*.net)".  Our MapWorks Surfaces module it's currently a two step process to get to ASC, Surface Manager to export the TIN to a file, then Surface Convert to convert the TIN to an Ascii Grid.  As I typed that I realized we need to add the conversion to the surface manager (a minute wasted).

[Neilw_05]

Basic ArcGIS can read DEM files so it would be a simple one step Export to DEM if it weren't for the defect.

[sboon]

Neil, what happens if you export to GeoTIFF instead of DEM?  Can ArcGIS use the GeoTIFF files?

Steve
Please use the Accept as Solution or Kudo buttons when appropriate

[Neilw_05]

Export to GeoTiff worked well on a small site I tested. I'll run some tests on a large DEM that gave me trouble and report back.

A Geotif will work just as well in ArcGIS as a grid and it won't require any conversion from an ASCII file, so there should be no reason to create an ASCII file in C3D.

[ouspensky]

The way I have been doing it for arcGIS is to export the TIN as LandXML then do a spline based interpolation off that TIN and convert to ESRI GRID.

To use the QGIS method you can import the LandXML then extract the points using the QGIS vector tools and use the GRASS function to create a RST surface then bring that back into QGIS and use the "saveas" option for that layer and save it to ESRI GRID

Also you can export the C3D TIN as a DEM or geoTIFF import that into QGIS and use 'saveas" to convert it to ESRI GRID  however the raster sampling in C3D is not so great.

in my opion a C3D to QGIS workflow is the best way because you don't have to pay out $$$$ to buy a special "conversion" extension and pay out even more $$$$ for a "3D Analyst" extension just to do a basic file conversion.  Also QGIS and GRASS are more stable for raster based operations than any ESRI product

[ksorsby]

I'd say there is a very good reason - I get asked more-or-less every day for surfaces as asc files now and I'm bored of fobbing the clients off or figuring our workarounds. ;o)

Kevin

[ksorsby]

Interesting. Ill have a look at the QGIS workflow you suggest when I'm next in work. It's a little annoying that C3D can import asc files but not export them.

Something about Geotiff that bothers me is that I am creating detailed models in C3D then having to apply a coarse grid across it, and then when it ends up in TUFLOW another cell grid is applied again at a different orientation. So the levels become less accurate as transfers happen. Is there a way of changing the grid rotation when exporting to Geotiff?

Cheers,

Kevin

[antoniovinci]

ouspensky wrote:

To use the QGIS method you can import the LandXML

---

Well, never heard about it, sir: which command do you use to open a C3D landxml file in Qgis..?

Please try with my attached example, thx.

[AllenJessup]

It may require a plugin - https://plugins.qgis.org/plugins/LandXml/

[antoniovinci]

---

AllenJessup wrote:

It may require a plugin - https://plugins.qgis.org/plugins/LandXml/

---

Thanks Allen, but that plugin expects a 2D LandXML, whilst we're talkin' about a 3D mesh by Autocad Civil (or my Map2006 too).

Let's wait for Ouspensky's elaboration...

[MikeEvansUK]

I have searched for a conversion but I don't think its that easy. You need to specify the rows & columns etc for ERSI.

It appears ArcGIS will use a simple xyz file but these need to be in squares. No intermediate triangles.

What I have done in the past to convert for the flood mapping guys is to create cogopoints on a grid overlapping the surface then elevate to surface. Keep the grid small to export as much surface detail as possible then export to an XYZ file. you will get the entire grid exported with the -9999 null values (NB may need to edit in excel to add or change these null entries)

Then you can then switch to map3d, generate a point cloud using the xyz file. Create a surface from the point cloud but switch the export to ERSI ASCII the surface file will be generated with the nrows & ncol details added.