And I've learned a bit about surveying, so thanks for that Flip :) As for 3D... As far as X3D Earth goes there is a proprietary implementation (Bitmanagement) that actually looks promising, at least as a proof of concept. If you're working with a local datum/projection, older datasets etc. (i.e. not Long/lat) then standard X3D in meters, or whatever arbitary unit you choose yourself would be a possibility. To my dissappointment the so called GeoNodes don't actually help until you've already churned your data through the long/lat mill comprimising it's accuracy for detailed work. If you want it FAST (to develop and deploy) KML is almost impossible to resist, and more or less free for now. If you want it OPEN World Wind can possibly be of use once you've got your data into WMS (bitmap drapped over low res heightmodel) If you want it ACCURATE, or that is to say in the original coordinate system, you're left with desktop GIS or "roll your own" possibly with X3D for net distribution. Please, please tell me I'm wrong if anyone has found a geo-spatially aware (read "understands coordinate projections") solution, opensource or otherwise for publishing limited 3D datasets in web pages. We'll probably be waiting a long time to see X3D Earth and then I'm not convinced it will be of much use in none-global (99.9%?), real world GIS projects. Cheers Pete Btw, no I wasn't at the first X3D Earth meeting unfortunately and by the second meeting it seems the spec was already decided. Shame really as it dosn't seem to tackle any of the actual cases I could have used it for.
_____ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Phillip C. Dibner Sent: 23 April 2007 23:46 To: [email protected] Subject: Re: [Geowanking] Open-source least squares network solution? Thanks for the response, Peter. Sorry if I was a bit cryptic. The notion is to take various measures that have been acquired at a series of points on the ground, using traditional methods of land surveying, such as angles between and distances to other points in the survey network or to points of known location, and to use these data to compute the location of each point. Typically, the computation looks like an overconstrained system of linear equations, and the output of the computation is the set of coordinates for each point that minimizes the sum of the squared distances between the location for each point and the locations as determined by the various combinations of equations that give a single, deterministic result for each point. (Was that obscure enough? The idea is that there are typically several sets of equations that will produce a location for each point, but the results are not consistent: depending upon which equations you use, you usually come up with a different location for each point. This is because the equations come from measurements that contain a certain amount of error.) I believe that there are many libraries that include one or more functions for least-squares fits to overconstrained systems of equations. What I have not found anywhere (yet) is open-source code that does the necessary data handling, i.e., that accepts the measurements taken at each point, converts them into a form suitable for doing the least-squares fit, and then provides output showing the coordinates for each point in the network, and the associated error (based on the difference between overall computed location and the various inconsistent, "partial" results for that point). This can be quite cumbersome if you do it by hand, and in general, the problem grows faster than linearly as the number of points increases. FYI, my application involves old data (definitely pre-GPS) from biological field surveys that relied on bearings taken with a compass, and often, from a combination of pacing and tape measurements between points. I anticipate a need for further hacking, which is one reason I'm looking for an open-source solution. There definitely are some similarities between my requirements and that of various visualization technologies, and in fact, I have found some open-source solutions for the latter. They don't quite fit my needs, but perhaps at some point, one will. Did not know/recall that the X3D Earth folks had an implementation yet, but I will inquire. Were you among the people at the X3D face-to-face at Ames that I attended? Apologies - I just don't recall. Thanks again for the message and the request for clarification. In the mean time, I'll be happy to hear from anyone who has a good lead. Flip On Apr 21, 2007, at 1:52 AM, Peter Strømberg wrote: Flip, could you describe what solving a survey network entails and how it would appear visually? I've just returned from the second meeting og X3D Earth working group who have big amibitions on the 3D visualisation side and an open specification and an excellent Java open source implementation. Please tell us more... Cheers Peter Strømberg www.hypergis.com _____ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Phillip C. Dibner Sent: 21 April 2007 00:45 To: [email protected] Subject: [Geowanking] Open-source least squares network solution? Hello all. I have been looking for some open source code that solves an arbitrary survey network in 2D. Least squares solution, with the ability to weight points, would be ideal. 3D wouldn't hurt either, but isn't necessary. I've been looking for a while, and found nothing that suits, or even comes close. Any pointers? This isn't readily available through any of the "well-known" packages like GeoTools, GRASS, PostGIS etc., is it? Thanks, Flip Phillip C. Dibner Ecosystem Associates +1 650 948 3537 +1 650 948 7895 Fax _______________________________________________ Geowanking mailing list [email protected] http://lists.burri.to/mailman/listinfo/geowanking Phillip C. Dibner Ecosystem Associates +1 650 948 3537 +1 650 948 7895 Fax
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