Hi Leyan
>I struggled quite a lot with the interface of a very famous commercial
GIS on this issue, I believe there is a real possibility to do better
here ! I think it is essential to allow the >user to change the
transformation later easily, maybe somewhere linked from the CRS choice
? That's where I would go as a user.
He, he, I bet it is the same GIS :-)
>I was also wondering how you see the relationship between CRS and
datum transformation. I use CRSs (all the Beijing54 CRS) which already
have a +towgs84 defined in their >definition, but several towgs84
coefficients are offered when loading the layer. It is confusing to have
to answer that, and if something else than the default coefficients is
chosen, >the result is incompatible with the proj4 definition. Should we
strip these CRS definitions of the towgs84 coefficients (which were only
meant for a small area initially, so are not >valid everywhere)?
Do you mean we should strip the towgs84 parameters from
tbl_srs.parameters or do you mean to deprecate/remove entries from
tbl_datum_transform?
>Also, do you see a need to allow to define a custom datum
transformation, or do you think it is enough that user can create a
custom CRS with different towgs84 parameters?
It is possible to add new entries to tbl_datum_transform to create
custom datum transformations. Yes, it would be more convenient to have a
gui for that, even if I don't know how often it will be used. You might
judge it better since you obviously have to deal often with CRS issues.
Regards,
Marco
On 24.02.2014 13:35, Leyan wrote:
On 02/24/2014 05:45 PM, Marco Hugentobler wrote:
- GUI: have a tab in project properties where non-default datum
transforms would be managed - instead of requiring the user to select
the datum transform immediately when the layer was added (and without
being able to change the decision later)
I don't have a strong opinion if it should be in project properties
or if the user should be asked immediately. The immediate selection
has been implemented following the behaviour of a commercial GIS.
However, the possibility to change it later easily does also sound
good to me.
Btw., congratulations to the merge of the multithreading branch!
Regards,
Marco
Hi Marco,
I struggled quite a lot with the interface of a very famous commercial
GIS on this issue, I believe there is a real possibility to do better
here ! I think it is essential to allow the user to change the
transformation later easily, maybe somewhere linked from the CRS
choice ? That's where I would go as a user.
I was also wondering how you see the relationship between CRS and
datum transformation. I use CRSs (all the Beijing54 CRS) which already
have a +towgs84 defined in their definition, but several towgs84
coefficients are offered when loading the layer. It is confusing to
have to answer that, and if something else than the default
coefficients is chosen, the result is incompatible with the proj4
definition. Should we strip these CRS definitions of the towgs84
coefficients (which were only meant for a small area initially, so are
not valid everywhere)?
Also, do you see a need to allow to define a custom datum
transformation, or do you think it is enough that user can create a
custom CRS with different towgs84 parameters?
Regards,
Leyan
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Dr. Marco Hugentobler
Sourcepole - Linux & Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
[email protected] http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee
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