https://proj.org/en/9.5/development/reference/functions.html#c.proj_factors You just provide the projected CRS, just created from the EPSG code. It converts it internally into the projection over its geographic.
On Thu, 24 Oct 2024 at 15:19, Roger Oberholtzer <roger.oberholt...@gmail.com> wrote: > On Thu, Oct 24, 2024 at 2:36 PM Javier Jimenez Shaw <j...@jimenezshaw.com> > wrote: > > > > The last versions also accept a projected CRS, extracting the projection > from it. > > I am using 9.4.0. Do you mean that I should be able to use this? > > proj_normalize_for_visualization(0, > proj_create_crs_to_crs( 0, > "EPSG:4326", > "EPSG:3006", > 0)))) > > If that's what you mean, it seems that the convergence values are not > as expected. Or do you mean something else? > > > > > On Thu, 24 Oct 2024, 14:27 Thomas Knudsen via PROJ, < > proj@lists.osgeo.org> wrote: > >> > >> Roger, > >> > >> The "factors" elements refer to a projection, not to a CRS > >> (the CRS includes reference frame information), and not > >> to a transformation (which describes a path between two > >> different CRS). > >> > >> So you should only call proj_factors on a PJ object obtained > >> from a plain classic proj(ection) string, i.e: > >> > >> p = proj_create(0, "proj=utm zone=33 ellps=GRS80"); > >> > >> > >> Den tors. 24. okt. 2024 kl. 14.11 skrev Roger Oberholtzer via PROJ < > proj@lists.osgeo.org>: > >>> > >>> Hi all, > >>> > >>> I have been using proj_factors in a couple CRS to get the > >>> median_convergence value. I need this when rotating a point that has > >>> been projected into the CRS. > >>> > >>> In my usual setup, I define something like the following (WGS84 (from > >>> a GPS receiver) to Sweref99): > >>> > >>> proj_normalize_for_visualization(0, > >>> proj_create_crs_to_crs( 0, > >>> > "EPSG:4326", > >>> > "EPSG:3006", > >>> 0)))) > >>> return(ISERROR); > >>> > >>> This works fine. I get the points I expect. But as I will need to > >>> rotate that point using data from the GPS (heading is true north), I > >>> need to know how that differs from the projected point's north. So I > >>> use proj_factors. As it turns out, I cannot use the definition from > >>> above to do this. The median_convergence value is wrong. So what I > >>> have been doing (for EPSG:3006 - it is CRS-specific) is defining > >>> something like this: > >>> > >>> proj_create(0, "+proj=utm +zone=33 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 > >>> +units=m +no_defs"); > >>> > >>> You will note that this is the implementation of EPSG:3006, but > >>> without +type=crs. Why without that parameter? Time. When including > >>> it, the proj_factors call takes around 60 times longer. This is > >>> extremely significant when generating, say, point clouds with hundreds > >>> of million points. A processing time of 15 minutes becomes 15 hours. > >>> The values provided are exactly the same. But one takes significantly > >>> longer to provide them. > >>> > >>> I see this effect in more than EPSG:3006. For example EPSG:5677. I > >>> suspect that it is generally the case. > >>> > >>> What I would like to do is something like this: > >>> > >>> proj_normalize_for_visualization(0, > >>> proj_create_crs_to_crs( 0, > >>> > "EPSG:4326", > >>> > "EPSG:3006", > >>> 0)))) > >>> return(ISERROR); > >>> > >>> proj_create(0, "EPSG:3006"); > >>> > >>> > >>> Where the first is used to project the point, and the second is used > >>> to call proj_factors for that point. > >>> > >>> This would allow a general solution, which is what I am after. So I > >>> either need to call something other than proj_create, or I need to see > >>> how to remove +type=crs in this context. > >>> > >>> Does this make sense? > >>> > >>> -- > >>> Roger Oberholtzer > >>> _______________________________________________ > >>> PROJ mailing list > >>> PROJ@lists.osgeo.org > >>> https://lists.osgeo.org/mailman/listinfo/proj > >> > >> _______________________________________________ > >> PROJ mailing list > >> PROJ@lists.osgeo.org > >> https://lists.osgeo.org/mailman/listinfo/proj > > > > -- > Roger Oberholtzer >
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