Land Surveying Photos

Measuring HI using a height meter

The usual case in measuring HI in Philippine practice is to use a steel tape. This is where elevation error propagation takes place where HI measurement is taken for granted.
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Thoughts

  • If each topo project that I undertake either for agri or for mining applications permits to run leveling in terms of cost (and requires high accuracy elevation values), then it would be great. I can have it included in my least squares adjustment in order to produce a topo map with purely topocentric height values.

    I got it! What you really mean by curvature correction is the vertical (geometric) one and what I am stressing all along is the geodesic effect of ellipsoid. Yes, you're right running level would be a great idea in order to get a glimpse of geoid for the project area. Having those vertical control points included in Least Squares Analysis then geoidal modelling is in the making. Cheers.

  • If ur project needs an accuracy of elevations better than 3rd order leveling accuracy,i think u hav to run leveling. Propagate Error in elevation can be corrected by applying propagation of error. This is commonly done in adjusting traverses in topo survey. Cheers

  • Measuring HI using slant steel tapes propagates error wether we like it or not. Of course, if the application is for huge agricultural plantation or municipal watershed mapping, then elevation error is not that important for as long as watershed variance does not affect or has minimum effect on the hydrology. This means that if hydrology is on the table, the surveyor is obliged to provide the best topographic map of consistent elevation values. Employing levels for the vertical control is a good idea but not needed in many if not all instances of topographic work should we employ the height meter, the GPS/GNSS for some control points, and the Least Squares Analysis for the entire project data. This is undoubtedly a cost saving methodology that does not compromise hydrology requirements. My experience in using the steel tapes says otherwise. Cheers.

  • Hi to all!

    Thats right height of instrument measured using steel tape,there is allowable accuracy adopted on this method. For topo survey this is good enough since levations of close and close circuit traverse are corrected. For a more accurate elevations you can run differential leveling in ist,2nd and 3rd order.Measuring HI using steel tape is a practice even in some other countries.

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