AltaLIS DEM: how to load into arcGIS

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01-15-2015 11:08 PM
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New Contributor II

I was wondering how to go about loading AltaLIS DEM files into arcmap? There are three ascII files with .ghl .gnp and .gsl extensions (masspoints, hard and soft breaklines).

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Occasional Contributor III

These file formats are not supported in ArcGIS. You can check list of supported raster file formats.

ArcGIS Help (10.2, 10.2.1, and 10.2.2)

I also checked it in ArcGIS data interoperability supported formats. No luck.

www.esri.com/library/fliers/pdfs/data-interop-formats.pdf

When I extracted the downloaded AltaLIS DEM sample files I found they are in dwg format.  So if you have dwg you can use these files to Create TIN or create raster surface using interpolation.  AltaLIS.png

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New Contributor II

Hi Kishor,

Please see DEM Terrain Products - AltaLIS to download one of the files I'm talking about. The files you show, I cannot find under DEMs...those are Provincial Base Maps, not DEMs.

Thanks,

--Terry

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Occasional Contributor III

I downloaded the data from provided link and found it has gnp, ghl and gsl file extensions. These file formats are not supported in ArcGIS.

The ZIP folder also contains a word document called DEM information.  This word doc talk about the format of these (gnp, ghl, gsl) files as well as how the information is stored in these files. As they are ASCII files so I simply opened them in MS Notepad and saved them as .csv file.

We can use following steps as workaround:

1. Open .gnp file in Notepad and save as .csv or .txt. When you will open gnp file in Notepad you will find the Object ID, X, Y, Z value information

2. Add csv file in ArcMap > Use the Display XY and plot these points and create a point feature class. While plotting use appropriate UTM zone ( NAD 1983, Zone 11N or 12 N)

3. Add other two files and use XY to line tool to generate lines

4. Use Interpolation to generate raster or Use Create TIN tool to have 3D surface.

Hope the above information is helpful.

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New Contributor III

I've been having troubling getting AltaLIS data into ArcMap in the right position and finally figured it out. I used the NAD83(CSRS) / Alberta 10-TM (Resource) projection.

false easting: 500000

false northing: 0

central meridian: -115

scale factor: 0.999199999999999980

latitude of origin: 0

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New Contributor

The website suggests NAD_1983_10TM_AEP_Forest. You can find this by searching in the Coordinate System search bar at the top. Same projection values (although scale factor is rounded) but potentially different GCS.

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New Contributor II

Thanks you for the steps, this is useful. I get stuck when trying to run the XY to line tool as there are only 3 fields that ArcGIS can read (Field11, Field13, Field17) and 4 fields are required: Start X Field, Start Y Field, End X Field, End Y Field. Has anyone been able to run the XY to Line tool successfully?

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New Contributor II

Did you ever figure a solution to your question? I am currently facing the same issue.

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Occasional Contributor

I stumbled across a better answer regarding the .GHL and .GSL files from AltaLIS on reddit; these file extensions are GENERATE format, which can be read and converted to lines by 'ASCII 3D to Feature Class'. The generated breaklines can then be used in conjunction with the .GNP files (which are more or less simply CSV/XYZ with an extra field at the beginning of each line) to create TINs which can then be converted to raster. 

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