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<div class="">I’d rather we have a opt-in solution than an all-or-nothing solution with regards to the grids.</div>
<div class="">There’s a few things we can do to make life a bit easier for everyone though:</div>
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</div>
<div class="">1. Some transformations absolutely require a grid to work and should fail if the grid is not found.</div>
<div class=""> This behaviour is already in effect if grids are not prefixed by @’s in proj-strings. Determing which</div>
<div class=""> grids are optional can be difficult, but at least any grid that is used to change vertical datum from</div>
<div class=""> an ellipsoid to a local height system should fail (case in point, in Denmark that’s a ~40 m vertical</div>
<div class=""> offset)</div>
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</div>
<div class="">2. For transformations with an optional grid usage, a warning should be issued stating </div>
<div class=""> “Grid xxx is missing, install proj-datumgrid-yyy package”. Grids not part of a proj-datumgrid</div>
<div class=""> package should be linked to if possible, otherwise give the user a friendly message saying</div>
<div class=""> that they are on their own.</div>
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</div>
<div class="">3. When a transformation is performed without a grid the accuracy of the transformation should</div>
<div class=""> be lowered. Possibly, this is already be done (I can’t remember and am too lazy to check).</div>
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</div>
<div class="">Not all of this is immediately possible. At the moment we lack a proper way of issuing warnings</div>
<div class="">to the user and it is probably not easy to come up with a list of transformations that require grids</div>
<div class="">versus ones where grids can be regarded as optional. This is out of scope for the upcoming 6.0</div>
<div class="">release but can be included in 6.1 if someone is willing to do the work.</div>
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<div class="">I have a dream that one day we will replace the datumgrid packages with a download service</div>
<div class="">where as many grids as possible can be served from. PROJ should have the ability to either</div>
<div class="">download grids when the need arises (or at least make it easy for users to do so themselves).</div>
<div class="">At this point it is just a vision and I am not particularly keen on taking on this task myself but I</div>
<div class="">would be very happy to see this happen within the next couple of years.</div>
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</div>
/Kristian<br class="">
<div><br class="">
<blockquote type="cite" class="">
<div class="">On 20 Feb 2019, at 15:14, Andrew Bell <<a href="mailto:andrew.bell.ia@gmail.com" class="">andrew.bell.ia@gmail.com</a>> wrote:</div>
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<div dir="ltr" class="gmail_attr">On Wed, Feb 20, 2019 at 9:06 AM Even Rouault <<a href="mailto:even.rouault@spatialys.com" class="">even.rouault@spatialys.com</a>> wrote:<br class="">
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<blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204); padding-left: 1ex;">
On mercredi 20 février 2019 08:12:34 CET Greg Troxel wrote:<br class="">
> Even Rouault <<a href="mailto:even.rouault@spatialys.com" target="_blank" class="">even.rouault@spatialys.com</a>> writes:<br class="">
> > With the vertconc.gtx grid available, you'll get<br class="">
> ><span class="Apple-converted-space"> </span><br class="">
> > $ echo "45 -100 100" | cs2cs -f "%.8f" EPSG:7406 EPSG:5500<br class="">
> > 44.99998071 -100.00039555 30.85853056<br class="">
> ><span class="Apple-converted-space"> </span><br class="">
> > Without it, you'll get just us-ft to metre for the vertical part:<br class="">
> > 44.99998071 -100.00039555 30.48006096<br class="">
><span class="Apple-converted-space"> </span><br class="">
> With the grids being in separate distribution files, it seems easy to<br class="">
> end up with them not installed.<br class="">
<br class="">
Yes, but as the number of grids is growing over time, putting them in a single<span class="Apple-converted-space"> </span><br class="">
package would be an annoyance for people who have local needs.<br class="">
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<div class="">People have so much bandwidth and space now...</div>
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<div class="">Perhaps it would be good to have the default be everything and allow a reduced set to be available for those who need that?</div>
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--<span class="Apple-converted-space"> </span><br class="">
<div dir="ltr" class="gmail_signature">Andrew Bell<br class="">
<a href="mailto:andrew.bell.ia@gmail.com" target="_blank" class="">andrew.bell.ia@gmail.com</a></div>
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