topic contour lines in grids in ArcGIS Spatial Analyst Questions

contour lines in grids

PetronilaMandeno — Wed, 30 Nov 2011 15:37:57 GMT

I wasn't too sure how to describe this problem, and there may be two different problems, so I just titled this with the terms above as that is the results that I get: in a hillshade of an elevation grid, it appears as if the contour lines are etched into it.

The original files are tiled ASCII grids delivered by a LiDAR contractor. The ASCII files are presumably created from the original LAS point cloud dataset. It appears that way when I look at the ASCII file in GlobalMapper (a GIS program) and zoom in and can see all the trails and cool divets and hills. Here's how the file looks in GlobalMapper:

I very nice surface.

Here's how it looks when I add it to ArcMap:

Not a very nice image.

As you can see, the data range is weird, from -2147483648 to 2147483647. However, if I export it from ArcMap to another data format (say, ESRI GRID format), I get this:

The data range is right now, but it's got this funky contour line thing going on, and if I apply an on-the-fly (or permanent) hillshade effect, it looks like this:

For the level of detail I can get in GlobalMapping on the original dataset, this is, of course, completely unacceptable.

I have 50 more of these tiles, all at .5m resolution. I need to merge this all into one surface and I can't very well do that at the moment and have it looking like someone drew it. I know I'm doing something stupid or overlooking some setting, but I've been working in ArcMap for years and this is the first I've come across this and I really don't know what I'm missing. Any clue?

Thanks in advance and my apologies for the size of the images. There doesn't appear to be a way to re-size them via the forum. 😞

Re: contour lines in grids

EricRice — Thu, 01 Dec 2011 15:41:44 GMT

Hi Esther,

There are a few things that stand out. First, the gray image with weird Min/Max values - that is an indication that your dataset does not have statistics. Please run the Calculate Statistics tool on that dataset, especially if that is the original. The second image that has the right values, but looks crummy... What were the settings when you exported? Lastly, the image you display from GlobalMapper is not a DEM - it's a color shaded relief (fancy hillshade), so the image you display at the bottom should look strange if you applied a hillshade function to a dataset that is already a hillshade.

Do you have the original DEM's? If not, all you should have to calculate stats.

Regards,
Eric

Re: contour lines in grids

PetronilaMandeno — Tue, 03 Apr 2012 22:10:08 GMT

Hello erictrice,

My apologies for never thanking you for your response. I didn't get an email notice that anyone had responded...better go check my settings. Anyway, I ended up merging the data in Global Mapper and importing into ArcMap, but I will try the Calculate Statistics next time.

Thanks.