Global Mapper v25.0

Is it possible to add slope in degrees and slope direction attributes to point cloud data.

We are creating slope maps for golf courses and uploading them on cesium. But we would like to load a slope map showing direction arrows and slope values in degrees. That is achievable but what l am not sure of is to add these slope attributes to the point cloud points we have sampled as possible hole positions. We want to be able to click on the point cloud in cesium and see those attributes. So the main issue is to assign those slope attributes to the point cloud is this possible with global mapper?

Best Answer

  • DerrickW
    Answer ✓

    It's possible....kinda.

    I don't believe the point cloud formats (LAS/LAZ) themselves hold slope values*, and I don't believe it's practical for your application. If a point cloud has a grid spacing of let's say 1cm, what good is it going to do a golfer to know the slope values between every point in the point cloud? They're looking for a generalization of that data.

    (*There is a way to do this in programs like Terrasolid, but I don't think the file formats actually support those attributes natively)

    As an example:

    Ortho


    Full Lidar point cloud, including noise, with a slope shader


    Same spot & source lidar, but binned (Median, 10pt spacing)


    The above is just to show that I don't think that you want to show the slope value for every point in your point cloud. There is a way to do it though, kinda....so let me know if you want to hear that explanation. The general idea would be to generate an elevation grid, create a tight grid of area features (like 6in x 6in), calculate the slope stats for those areas, convert your point cloud to a CSV, and then add the attributes of nearby area features (with slope values) to each point in the CSV. The catch is that you're no longer in a point cloud file format and if you export those points back out to a LAZ/LAS format, the attributes you just calculated won't come with them.


    Alternatively -

    Create an elevation grid with an appropriate XY spacing (My personal opinion is something in the range of 5ft-25ft)


    Create a grid of area features:



    Calculate elevation/slope stats


    Your area features now have slope stats available:


    Create points at the centroids of your area features. Centroids will carry the same attributes



    The above walkthrough is just one of many ways to get what you're after (and there's a ton in Global Mapper!).


    These symbols aren't going to transfer over when you put them in Cesium though (Unless Cesium lets you display point symbols by applying a rotation & magnitude attribute to use. If that's the case, just make sure you convert the AVG_ASPECT attribute to a numeric value).

    One way to get this into Cesium would be to render out your imagery + scatter plot/slope arrows to a Geotiff and just hosted it as a raster layer.





    If Cesium works like ArcGIS Online Maps, you could just upload your CSV of points with slope attributes and display them that way (I don't have a layer online where I can show you, but you get the idea).


Answers

  • I am not familiar with Cesium, but typically if I wanted to Explore / Review / Edit slope and elevation data I would create a DEM from the point cloud. Spatial Operations using DEMs seem to give much more analysis options. maybe could load a DEM and point cloud into cesium using point cloud for visual and DEM for Data.

    From my experience in Global Mapper you can only do Lidar / Point Cloud operations on Point Cloud Data and they do not operate the same as a normal "point" for analysis / attribute functions.

    as a mentioned I do not know Cesium but maybe this will give you some different ideas.

  • Okay thanks how about expressing slopes as ratios is that possible in Global mapper. For example a slope of 25% should be expressed as a 1:4 slope. Can Global mapper display Slopes as Ratios.

  • It seems attributes such as slope values can be added to a point cloud as attributes which is what I wanted to do but it seems its not possible but thats what I wanted to do. Now on a different note my client wants slopes displayed as ratios for a specific project not degrees or percentages.

  • CORRECTION "It seems attributes such as slope values can't be added to a point cloud as attributes"

  • Thanks so much for a detailed response. I do slope maps for a client who asked me if it was possible to append slope attributes to a point cloud. Ussually its 365 points per green not every cm. So l create my elevation grid, then a slope shader with custom colors, ensure that l have about 365 points per green and calculate elevation statistics and plot the slope arrows which l overlay on the slope shader and export as a tiff. Pretty much the same workflow.