topic Re: converting contour lines to DEM in ArcGIS Mapping and Charting Questions

converting contour lines to DEM

RickCheney — Wed, 08 Jun 2016 22:27:41 GMT

I am using ArcMap Desktop. I have a shape file with contour lines for about eight lakes in an area of about 15 square miles.

The picture below is to give an idea of the distance between lakes and the picture at the bottom is a more zoomed in view of some of the lakes. I already have DEM data for the white area in the pictures. I would like to use the contours lines in the lakes to make DEM data which I could then adjust to make the shallower water light blue and the deeper lake depths a darker blue.

I tried using the TopoToRaster tool but it thinks the area between the lakes is part of the lakes and make dem data for the entire area. Can the TopoToRaster tool do only the lakes with the contour lines? How? Or, is there there a better tool for this?

Re: converting contour lines to DEM

DanPatterson_Retired — Wed, 08 Jun 2016 22:43:02 GMT

If you want to stick with vector, then you can have a look at Creating fill symbols—Help | ArcGIS for Desktop

Re: converting contour lines to DEM

RickCheney — Thu, 09 Jun 2016 00:22:52 GMT

Thanks Dan, I don't need to stick with vector, whatever will do the job best. Is there a better (raster) way to use the contour lines to show lake depth?

Re: converting contour lines to DEM

DanPatterson_Retired — Thu, 09 Jun 2016 01:54:12 GMT

For map making and not analysis, I would just overlay the vector lakes over the raster. Your lakes are too small to effectively show the depths unless you used an incredibly small cell size and topotoraster and then combined the dem and the raster lakes (using con). The rasters would have to the same cell size, which would cause issues with the dem since it probably isn't at the same resolution as would be required for the lakes.

Re: converting contour lines to DEM

RickCheney — Thu, 09 Jun 2016 02:13:27 GMT

I see what you mean, if I did succeed, the result would be so great. I guess I'll just use the contour lines the same as contour lines on land and forget about changing the water color depending on the water depth. I will add the labels showing the depth. The image below is the size that the printed map will be. Hopefully, when you click on the image you will get a full size version.

Re: converting contour lines to DEM

curtvprice — Thu, 09 Jun 2016 04:01:15 GMT

Topo To Raster is the tool you want. It is a spline interpolator so it needs to create a continuous surface.

I suggest converting the lake polygons to line and assigning them an elevation on the coastline (0 if these are depth contours), and add them to your contour data set. Then run Topo To Raster and clip the results to the lake areas.

Re: converting contour lines to DEM

RickCheney — Thu, 09 Jun 2016 14:00:46 GMT

Thanks Curtis, I agree with Dan that the lakes are small and the contour lines are tight so the effect might not show up much on the map but I'm new to all this and I am interested in checking out this option for future use and also to see how it looks on the largest of the lakes. I found some good instructions on converting polygons to line at the link below, but I couldn't find anything about assigning an elevation. Is Elevation one of the properties after I convert to line? Or, is the elevation the z-factor or something like that? It sounds like I assign elevation to the entire line shape file (or whatever is output from the conversion tool) and that elevation is used as the base level that the contour lines drop down from.

http://desktop.arcgis.com/en/arcmap/10.3/tools/data-management-toolbox/polygon-to-line.htm

Re: converting contour lines to DEM

curtvprice — Fri, 10 Jun 2016 01:08:12 GMT

If you go the polygon to line route you would have to use left-right topology to assign min and max elevations to the polygons. This is a little bit challenging database wrangling but it is doable, using the left and right poly object ids to do joins.

Re: converting contour lines to DEM

MikeCusi — Fri, 10 Jun 2016 04:12:32 GMT

You could also create 2 sets of "DEM's" one for the land part with an appropriate color scheme for land areas and with the lake areas masked out and converted to NODATA. The second "DEM" (bathymetry) for the lake part also with an appropriate color scheme and with the land areas masked out and converted to NODATA. You would have to make sure though that your lake bathymetry data is using the same datum as your land areas (as in reality the lake shoreline may not be 0m or 0 elevation) and that they are of the same pixel sizes and pixel position so that a snap raster is very useful when you create them. When you load them both into Arcmap (doesn't really matter which one is on top), just make sure to set the symbology for both nodata areas in each DEM as no color.

Re: converting contour lines to DEM

RickCheney — Fri, 10 Jun 2016 22:03:38 GMT

I think I can figure out how to mask the lakes out of the DEM data. Then, how do I mark the "no data" area? Also, I have a shape file with contour lines for the lake depths, what order are the steps to convert to DEM and mask out everything but the lakes with contour lines? Do I first use TopoToRaster, and does that give me a shape file? Then do I mask the shape file leaving only the lakes with depth data, then, somehow mark the non-lake depth areas as no-data?

Re: converting contour lines to DEM

MikeCusi — Sun, 12 Jun 2016 21:30:40 GMT

You can use the Set Null (spatial analyst) tool to define areas of "no data". You should do the no data/NULL ing only after you've created both the bathymetry and /terrain DEM rasters. your outputs should all be rasters not shapefiles. You could also merge the bathymetry and terrain DEM rasters but it will be a pain getting the symbology/color ramp to work right. Keeping them separate and just using no color for NULL/no data pixels will be easier by displaying them at the same time but with their own separate color ramps. I would also probably include the lake shoreline as an outline with no FILL color (as a shapefile if you want) so you can give it a distinctive color/width that will allow you to highlight it against the terrain /bathymetry.

Re: converting contour lines to DEM

RickCheney — Sun, 12 Jun 2016 22:11:31 GMT

Thanks for the help. Sorry, for all the questions but this is all new to me. I already have a terrain DEM raster. After I create the bathymetry DEM raster, then I use the Set Null feature of the Spatial Analyst tool to define areas of "no data", do I define the areas of no data on the newly created bathymetry DEM raster and also on the terrain DEM Raster that I already have? For the bathymetry, everything not in those lakes is no data and for the terrain, the specific lakes on the bathymetry raster get marked as non data?

Re: converting contour lines to DEM

MikeCusi — Sun, 12 Jun 2016 23:13:06 GMT

Yes.

Re: converting contour lines to DEM

RickCheney — Thu, 16 Jun 2016 17:21:04 GMT

Sorry for the delay, I won't be able to work on this until the weekend.

Re: converting contour lines to DEM

myname — Tue, 27 Dec 2016 08:57:37 GMT

You can create TIN from contours

Then convert TIN to DEM

This clip will help you Coutours to DEM in ArcGIS - YouTube

Re: converting contour lines to DEM

RickCheney — Tue, 27 Dec 2016 14:51:46 GMT

Thank You! I just watched the video and it looks like it will work great. I will try it later today and report back.

I learned from the video that you can drag and drop from the Table of Contents (on the left side of ArcMap) to the pop-up window of whatever tool you are using.

Re: converting contour lines to DEM

curtvprice — Tue, 27 Dec 2016 18:32:11 GMT

Rick, just looking at your screenshot, I wanted to warn you to make sure your output coordinate system is set to a projected coordinate system -- interpolation using unprojected (geographic) coordinates is usually invalid because distances on the ground in x and y are different, especially so at high latitudes.

Re: converting contour lines to DEM

RickCheney — Tue, 27 Dec 2016 18:50:47 GMT

I'm new at this and learning as I go. Is there anything I should do differently? Or, should I just try your solution and see how it works? If it makes a difference the area is Quetico Provincial Park on Ontario, Canada, I'm not sure if that qualifies as high latitude.

Re: converting contour lines to DEM

curtvprice — Tue, 27 Dec 2016 18:58:02 GMT

Ontario is far enough north, though you should probably work in projected space anywhere -- see how your hydrography looks squished out in your screenshot?

Just before you run these tools, go to Geoprocessing > Environments and set the output coordinate system to a reasonable projection for that part of the world. UTM (use the proper zone, and probably NAD83 datum) is always a good default choice unless your study area is really wide east to west (> 500 km) You also want to change the data frame coordinate system to a projected coordinate system.

What are projected coordinate systems?—Help | ArcGIS Desktop

Re: converting contour lines to DEM

RickCheney — Wed, 28 Dec 2016 00:42:41 GMT

I watched the You Tube video create raster/ DEM from coutours line in arcgis - YouTube and now that I am at my computer with ArcMap running, now I am getting an error message stating: "This video is no longer available because the YouTube account associated with this video has been terminated"

I can't remember the details of the video. It seems like a tool was used to create a "TIN" from the vector shapefile of the lake depth contour lines. Then, the TIN was converted to ?? something? Does anyone else get the YouTube error message? Do anyone see the video and remember which tools were used?