<br><br><div class="gmail_quote">On Wed, Aug 19, 2009 at 5:53 PM, Eric B. Powell <span dir="ltr"><<a href="mailto:ebpowell.chip@gmail.com">ebpowell.chip@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
ILAN BENISTY wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div><div></div><div class="h5">
Hi,<br>
<br>
I am dealing with a problem where I am importing an AutoCAD description of an airport (DXF) into PostGIS.<br>
I have a Python script which will import each coordinate to a PostGIS geometry with SRID = -1 (since I do not have real world coordinates, but Cartesian coordinates from a point of origin).<br>
I do, however, have a lat/long reference point, which represents the origin of my x/y CAD coordinates.<br>
I would like to be able to store my CAD coordinates points as Long/Lat (SRID=4326).<br>
Any suggestions?<br>
<br>
Thanks,<br>
<br>
Ilan<br></div></div>
------------------------------------------------------------------------<div class="im"><br>
<br>
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</div></blockquote></blockquote><div><br>I'll answer for Ilan, we work together<br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="im"><br>
</div></blockquote>
What country is the site in? What units are used for the drawings grid? Do you know the geographic datum?</blockquote><div> </div><div>Country: Canada, Units: meters, Datum: WGS84<br><br>I expect the solution is straightforward, but it is not obvious to us.<br>
<br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>
It may require a fair amount of pre-processign before the data can be accurately (de)projected to LatLong.<br>
<br>
Once the details of the drawing grid are known, there is a python wrapper for Proj4 which could be used to (de)project the points on the way into the database.</blockquote><div><br>We are very experienced programmers, but have a limited knowledge of SQL. We've been working with it for a few years, but at this point have been able to get by quite nicely with the basics.<br>
<br>We have a fair knowledge of Geodesy. It was my major, 20 years ago.<br></div><div><br>--<br>I'll give you the use case:<br><br>Currently we have a geometric database using PostgreSQL geometry types to represent aerodromes. The origin of the grid is the centroid of the aerodrome, and that we have a Geodetic position for. We use it, amoung other things, to plot radar targets. The radar data arrives on the same grid, so up to this point our data registers, we display the live radar data as SVG in any browser that is not IE with one second updates. This works well.<br>
<br>However, for many reasons, we have to go to a geodetic system. We'll still use the same metric grid with an origin at the centroid for radar data, but to integrate with other systems we must maintain a geodetic database.<br>
<br>The aerodrome data arrives as DXF. We have written an import filter in Python that parses in the DXF and converts it to Postgresql geometry. It also maps the layer names to a standard. Ilan, the author of this thread, is tasked with converting this to PostGIS so that we may merge with other systems that maintain geometry in WGS84.<br>
<br>The general coverage of the data is three or four kilometers. Surface radar data arrives at a resolution of one meter, so if our accuracy is within 10cm we are more than good. We assume a reasonably accurate centroid position and a Cartesian plane that does not extend more than 3 kilometers in any direction from the origin, so curvature error is not an issue.<br>
<br>--<br>The problem:<br><br>We have a metric cartesian data set.<br><br>We have a geodetic coordinate for the centroid of the aerodrome, which is the origin of our metric Cartesian data.<br><br>We need to convert this to geodetic to exchange data with other components of the air navigation system.<br>
<br>--<br>It seems to me that the solution might be to have PostGIS give us a coordinate for the centroid, transform the DXF coordinates during the parse operation, and then import it into PostGIS.<br><br>We don't know how to properly do that, and it's quite possible that that is not the ideal solution.<br>
<br>As I said, we are new to PostGIS, but we are keen to play.<br><br> </div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><br><font color="#888888">
<br>
Eric</font><div><div></div><div class="h5"><br>
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</div></div></blockquote></div><br><br clear="all"><br>-- <br>Cheers!<br>Rick<br><br>