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I'm a water resources engineer with literally zero GIS experience. I'm working as a volunteer on a Engineers Without Borders project delivering safe drinking water to a remote community, where my team has provided me GPX files for point of interest, tracks, and LiDAR contours.

In order for me to use the QEPANET plugin (to build a hydraulic water distribution model), I must first add a DEM. The problem: I don't know how to take my LiDAR GPX file and make a DEM out of it, and afterwards, superimpose the points and/or tracks on that DEM.

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    Before you start following the steps in Saijin_Naib's excellent answer, may I suggest step 0: Ask for a DEM from the team that provided the other GIS data. They may already have one, and just didn't realize you would need it. – csk Nov 6 '19 at 20:24
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    Solid idea, and I have, but haven't hear back. Thank you for your reply! – Joshua Nov 6 '19 at 21:00
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The question is a bit vague, so I'm going to focus my answer specifically on how one would generate a LiDAR-derived DEM raster product from a GPX that (apparently) contains LiDAR elevation contours.

1) Add the GPX to QGIS using the Data Source Manager by choosing Vector -> File enter image description here

1A) Pre-process/cleanup data (Likely out of scope for you)

1. Fix Geometries
2. Reproject to local CRS/GRS
3. Simplify to required spatial resolution

2) Choose an appropriate interpolation method from the myriad tools, bearing in mind that many expect/require points not lines as input data (and you hinted at lines above). The QGIS IDW and TIN interpolation algorithms will handle lines.
enter image description here

Anecdotally, I found IDW to be sufficient in my past research making LiDAR-derived DEMs.

2A) Setup interpolation (interpolated attribute, data type, interpolation method, processing extent, output resolution, required products, etc.) enter image description here

3) Iterate/experiment

4) Re-add the other data-types from the GPX file(s) as new layers, symbolize, subset with Filters, arrange, etc.

Example data/products:

LiDAR Contours enter image description here

Converted to points enter image description here

TIN Interpolation from points (linear interpolation) enter image description here

LiDAR DEM from original data provider (Derived from Lidar Point Cloud) enter image description here

The two are VERY close.

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    As Saijin_Naib has correctly summarized, there will likely be multiple steps required to accomplish your goal. Since you are new to GIS, those steps may be overwhelming. I have a lot of GIS experience, and coincidentally have an opening in my schedule for the next week or two. I'd be happy to volunteer some of that spare time to help you get underway. If interested, reply with your contact info and I'll get back to you outside of S.E. – Stu Smith Nov 5 '19 at 20:57
  • What a kind offer, @StuSmith. I'd like to take you up on it! It will help our volunteer team greatly to get the mapping situated, so we can move on to the hydraulics. How do we communicate offline? – Joshua Nov 6 '19 at 20:46
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    @Joshua, please send me an email at wagmorebarkless@protonmail.com – Stu Smith Nov 6 '19 at 23:03
  • @StuSmith, I've sent you an email. Thank you. – Joshua Nov 7 '19 at 15:20

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