Creating Surface from GEOTIFF DEM

[Raisk]

Hi All,

I have downloaded a DEM. Its in TIFF format. The tile Covers around 100 Sq kM 2D area but when imported to Civil 3D it shows 1sq m 2D area and 7538 sq m 3D area What does it mean? . Do I need to scale it before working? How It is done? I am attaching the tiff file and Civil 3D File as well.

Thanks!

[Pointdump · Accepted solution]

Santosh,

A couple of problems. 13,000,000 points is a huge DEM. And your DEM uses Geographic Coordinates--Lats and Longs. That DEM won't be usable until you assign a Coordinate System to your Drawing, which will allow Civil 3D to Transform.

What year C3D do you have? If you have 2016 or 2017 you're in luck. @Alfred.NESWADBA made a <<<Good Video>>> of how to use such a large DEM.

So what Coordinate System will you be using?

Dave

[Raisk]

Dave,

This DEM is of Indian subcontinent. And in drawing settings there are many coordinate systems available for India category. So How do we decide which coordinate systems is to select for particular DEM File. Do we get this information while downloading the DEM from the data source. I have downloaded this DEM from: 

http://bhuvan.nrsc.gov.in/data/download/index.php.

Also as I said it comes as sq m in size. Please tell me about scaling it to correct size.

I am a beginner and your help would be appreciable.

Thanks!

[Pointdump · Accepted solution]

Santosh,

Since your DEM appears to be in "LL84" Geographic Coordinate System (I'm only guessing here), you can use
UTM84-43N. <<<This Site>>> will help you make that guess. You'll want to get the Metadata (Data about Data) from the website you downloaded the DEM from. They usually have a "Readme" file or "Metadata" link.

From Help here's how to <<<Change the Specified Coordinate System of a DEM File>>>. Be prepared for some waiting time. That DEM is huge.

Dave

[Raisk]

Thanks ! Dave

It's pretty much clear to me now.

[Raisk]

Hi Dave,

One more question. The DEM tile shows  100km x 100km on the map while downloading. It appears 1m x 1m in drawing. How to scale it to show the actual area and work on it? Is it possible to download smaller tile.

Thanks!

[Pointdump]

Santosh,

Using the Measurement Tool in the free <<<GeoViewer>>> your GeoTiff is approximately 100KM Square:

So please show the exact steps you are using to put that GeoTiff into Civil 3D.

Dave

[Pointdump]

Santosh,

Civil 3D is confusing Lats and Longs with Northings and Eastings, so that is why your DEM only looks like a Meter Square.

I've tried several ways to bring that DEM into Civil 3D, but the only way that correctly places it is to use _MAPCONNECT.

Dave

[Raisk]

Hi Dave,

I simply go to "create surface from DEM" and select the GEOTiff file. It would be helpful if you tell me the step to bring in the tiff file into model and create surface from it.

Thanks!

[Pointdump]

Santosh,

I tried a few different ways to create a surface from that huge GeoTiff, but was unable. Not sure exactly what the problem is, but Civil 3D just can't seem to correctly import that Geographic CS(Lats and Longs) GeoTiff into a Projected CS(Meters) drawing. I even tried using _MAPCONNECT to bring it in using "Add Raster Image or Surface Connection". No go. Maybe someone here can chime in with something clever.

Dave

[Raisk]

Thanks!

[Pointdump · Accepted solution]

Santosh,

OK, I was able to use QGIS to re-project that LL84 DEM to UTM84-43N. Then I was able to create a surface in Civil 3D. Re-projected GeoTiff attached.

Dave

[Raisk]

Yes, Now it comes to actual size.

Thanks a Lot Dave !

[codee]

@Pointdump 

Hello Dave. I have run into a problem again and was looking for some assistance. Recently the USGS changed the format of their DEMs to ".TIF" I have downloaded the Tif file which has 117,000,000. I have created a surface and added a data clip boundary to make the file manageable upon import. However when I try to add this TIF I I do not get the information I was looking for (It says the ranges are too large and there is no surface definitions). I am essentially using the same process as I used to use with ADF files.

Here is a drop box link to the TIF file. Also included in this post is a picture of my settings. 

https://www.dropbox.com/t/PWnlEOsAEULWIezj

If you could help me figure this one out I would really appreciate it. 

Cody

[codee]

@Pointdump 

If it i sthe same issue the other gentleman was having I am wondering if you of a tutorial or instructions on how to use QGIS to reproject the TIF to a new coordinate system. Thanks.

[Pointdump]

Hi Cody,
Drag-n-Drop that USGS_13_n39w122.tif into QGIS. Save, changing the Coordinate System.
You can also clip the Tiff in QGIS, which saves you the step of a Data Clip Boundary.
If you get stuck, post a drawing in your preferred Coordinate System and a Rectangle around your area of interest.

Dave

[codee]

@Pointdump I was able to get it to come in but the data seems to be pretty corrupt. I tried it on a project I still had the ADF for and compared the two. The estimated points also increased from 117,000,000 to 121,000,000 after transforming the coordinate system... however the data seems like it lost points. They are also off by up to 5' from one another. I will post a drawing with the file made from the old ADF compared to what I got from the TIF. Hopefully there is some step I am missing. The drop box link will contain the ADF file, the original downloaded TIF and the transformed TIF as well as a drawing with a surface from both the ADF and the TIF. 

Here is the drop box link:

https://www.dropbox.com/t/WsQITr31yRb52U8i

[Pointdump]

Cody,
"...off by up to 5' from one another."
That's probably the difference between displaying center of pixel or corner of pixel. I don't know any program that allows you to choose, so if you need greater accuracy, go looking for LiDAR Data from >>>NOAA<<< or >>>TNM<<<.

Dave

[codee]

sorry, I meant 5' in elevation.

[Pointdump]

Cody,
Attached, please find a ReCap file, Codee_1.rcp, which contains 86,123 Ground Points, that you can use to create a Surface in your drawing. To get that, I merged and clipped two larger Point Clouds to fit your Surface Boundary. Before you import the ReCap file, change UNITS to "US Survey Feet".
Dave