GRID versus TIN

KurtMKurtM Water Resources EngineerPosts: 11Trusted User
edited August 2013 in Vector Data
I've been working with bathymetric (lake/river bottom) data lately and have some thoughts on creating surfaces from survey data collected at non-consistent spacings. I wonder if there is a way to create a Triangular Irregular Network (TIN) surface from point data rather than a 3D GRID?

My coworker and I have done a few trials creating 3D surfaces from inconsitently spaced survey data using both Global Mapper, and River2D's bed and mesh generators. (Note: River2D is free hydrodynamic modelling software which includes functionality for creating surfaces). We found that Global Mapper creates good surfaces when the survey data is more or less evenly distributed and spaced. However, our bathymetry surveys usually consist of point data collected in Continous Topo mode by piloting a boat back and forth in a series of parallel lines along shore. So, even though points in a line may be only 2 m apart, discrete lines of points may be 50 to 100 m apart. Creating a surface using the 3D GRID tool in Global Mapper works okay, but requires quite a bit of breakline (3D polyline) generation, and an iterative process where a surface is created, the origional data is edited, and a new surface is created, etc. It's nice to be able to manual specify the grid resolution, or to allow GM to chose what it thinks to be an optimal resolution. However in the end, your still forcing the irregularly spaced data to be represented by a square grid of finite X,Y spacing. One can shrink the grid spacing to the absurd, but then you end up with larger files - still not ideal.

We've found that River2D generally creates nicer surfaces since they are true Triangular Irregular Networks (TINs) rather than fitting a square grid to non-square data. Additionally, in River2D, breaklines can be specified after the surface is created, and the surface can be immediately updated without having to be regenerated. The down side of using River2D, is that data has be be passed back and forth between the two programs. Additionally, River2D is not intended to contain additional attributes for each point. So the output surface from River2D must have attributes for the individual points re-appended, which is very awkward and a potential source for error.

Is there a way to create a TIN directly in River2D or to dynamically edit a GRID surface once it's been created without going back to the source data and manipulating it?

Thank you,
Kurt

Comments

  • KurtMKurtM Water Resources Engineer Posts: 11Trusted User
    edited August 2013
    I neglected to post a link to the River2D page. Here it is:
    River 2D Description
    River2D Hydrodynamic Model for Fish Habitat
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited August 2013
    Kurt,

    The gridding process in Global Mapper actually creates a TIN as an intermediate product, then samples the TIN to create the grid surface. There is a checkbox option when gridding the data to save the TIN as its own layer. If you have the TIN as a layer you could edit that directly, then grid the modified TIN layer rather than gridding from the original points. That should be pretty fast as the latest versions of Global Mapper don't need to re-TIN if you are gridding a layer that only has triangles in it already.

    Eventually we may add support for doing terrain operations right from a TIN surface, but for right now they have to be gridded to do any analysis like contouring, volumetrics, or watersheds.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
Sign In or Register to comment.