Re: What coordinate system should I use?
- From: Happy Trails <nomail@xxxxxxxxxxx>
- Date: Mon, 10 Mar 2008 17:16:13 -0500
On Sun, 9 Mar 2008 18:22:51 +0000, Dominic Sexton
<{d-sep03}@dscs.demon.co.uk> wrote:
You might get more helpful answers if you tell us what you already use
and what you hope to achieve with your augmentations.
Use lat and long and spherical trig for calculations. If you need to
display the output on / as a map you will need to use and appropriate
projection.
You may be interested in the partial source code available for
GPSMapEdit:
===============
Dominic,
One particular function which has got me thinking about this more than
anything else is the production of contour lines for topographical
mapping. Terramodel is the best software around for this in terms of
flexibility and what you can do with it, but it has some limitations.
Until recently, with the survey-related work I had done, I could not
even see any need for contour lines except to reproduce on a printed
map, which in my case was just to show the client a pretty picture he
could understand, to justify our billings. All I ever wanted for
stakeout and other uses was the TIN. Now that I am doing some gps
mapping, I understand how useful contours can be.
Because of the antique arithmetic code in Tm, which Trimble has never
bothered to update in the dozen or so years they have owned the
product, it is a bit slow when processing more than a few hundred
thousand points. It is a tool for surveyors, and works very well for
surveyor-sized dtm's, but when you get millions of points, it just
poops out.
Plus, if you want the contour module incorporated into your copy of
Terramodel, you have to have a licenseable, dongle version - minimum
cost $1000 for the Tm CAD pack, plus pay the extra $500 for the
contour module. Like DEM2TOPO I would like to make something
available as "BeerWare", but I don't like beer, so I guess it would
have to be "CubaLibreWare", if you know what I mean.
I thought I might create a contour drawing program to start with, that
would read .HGT files, and have most if not all of the contour
functions of Terramodel. I know there are several contouring programs
around, but none of them have the rich set of features that Tm has
with the possible exception of later versions Global Mapper, which I
have not seen.
I do not have the contour module in my own "free" FDM version of
Terramodel - no dongle - so if I want to produce contours I have to go
to the office and do it on the full-featured version there. It's a
pain, and it has the limitations noted above.
Good suggestion on the source code for GPSMapEdit. Do you have any
idea in there where I might be able to review the code for calculation
methods used, and numerical accuracy? People have commented that it
uses Lat&Lon degrees with 5-decimals accuracy - can anyone verify
that?
- Tom
.
- References:
- What coordinate system should I use?
- From: Happy Trails
- Re: What coordinate system should I use?
- From: Dominic Sexton
- What coordinate system should I use?
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