[Gvsig_english] BUG: gvSIG 1.9 (Build 1253) Image Filtering
Simon Cropper (Botanicus Australia Pty Ltd)
scropper at botanicusaustralia.com.au
Thu Dec 17 23:20:52 CET 2009
Sergio,
:-D very good!
I suppose I was looking for this answer (after reading a bit more and a
sleeping on the issue)...
Datum: WGS84, GDA94, AGD66
Coordinate Reference System: lat/long, northing/easting
Projection: Azimuthal Stereographic Projection, Gnomonic Projection,
Miller's Cylindrical Projection, Equal-area Conic Projections by Lambert
and Albers, Wiechel's Projection, Transverse Mercator, Lambert Conic
Conformal (2SP), etc
Here is a link I found that has some fantastic visual representations of
each type of projection... Cartographical Map Projections
<http://www.progonos.com/furuti/MapProj/Normal/TOC/cartTOC.html>
Also, in the SRS Info section of the reprojection facility, some EPSG
Codes show the projection. For example, EPSG 20255
Code of selected SRS: 20255
Repository: EPSG
SRS name: AGD66 / AMG zone 55
Projected: Yes
Datum name: Australian Geodetic Datum 1966
Ellipsoid: Australian National Spheroid
Semi-major axis 6378160.0
Inverse flattening 298.25
Prime meridian: Greenwich
Meridian of longitude 0.0
Projection: Transverse Mercator <<<<<<<<<<<<<<<<<<<<
Parameters
semi_major 6378160.0
semi_minor 6356774.719195305
central_meridian 147.0
latitude_of_origin 0.0
scale_factor 0.9996
false_easting 500000.0
false_northing 1.0E7
PROJ4 string: +proj=tmerc +lat_0=0.0 +lon_0=147.0 +k=0.9996 +
x_0=500000.0 +y_0=1.0E7 +ellps=aust_SA +units=m
If I look at EPSG 3100
Code of selected SRS: 3110
Repository: EPSG
SRS name: AGD66 / Vicgrid66
Projected: Yes
Datum name: Australian Geodetic Datum 1966
Ellipsoid: Australian National Spheroid
Semi-major axis 6378160.0
Inverse flattening 298.25
Prime meridian: Greenwich
Meridian of longitude 0.0
Projection: Lambert Conic Conformal (2SP) <<<<<<<<<<<<<<<
Parameters
semi_major 6378160.0
semi_minor 6356774.719195305
central_meridian 145.0
latitude_of_origin -37.0
standard_parallel_1 -36.0
false_easting 2500000.0
false_northing 4500000.0
standard_parallel_2 -38.0
PROJ4 string: +proj=lcc +lat_1=-36.0 +lat_2=-38.0 +lat_0=-37.0
+lon_0=145.0 +
x_0=2500000.0 +y_0=4500000.0 +ellps=aust_SA +units=m
but if you look at EPSG 4202...
Code of selected SRS: 4202
Repository: EPSG
SRS name: AGD66
Projected: No
Datum name: Australian Geodetic Datum 1966
Ellipsoid: Australian National Spheroid
Semi-major axis 6378160.0
Inverse flattening 298.25
Prime meridian: Greenwich
Meridian of longitude 0.0
PROJ4 string: +proj=longlat +ellps=aust_SA
or EPSG 4283...
Code of selected SRS: 4283
Repository: EPSG
SRS name: GDA94
Projected: No
Datum name: Geocentric Datum of Australia 1994
Ellipsoid: GRS 1980
Semi-major axis 6378137.0
Inverse flattening 298.257222101
Prime meridian: Greenwich
Meridian of longitude 0.0
PROJ4 string: +proj=longlat +ellps=GRS80
You see that it does not state that the SRS is projected and no
projection is given. In fact, if I am getting the grasp of this stuff,
_this is actually incorrect_ - all representations of the earth in 2D
are a projection. The above two are actually "cylindrical projections"
(see here
<http://www.progonos.com/furuti/MapProj/Normal/ProjCyl/projCyl.html>) -
they are probably not flagged as projected because no computation is
done on the raw coordinates 45°N is +45, 34°S is -34, etc.
Am I on the right track?
Cheers Simon
Simon Cropper
Botanicus Australia Pty Ltd
PO Box 160, Sunshine, Victoria 3020.
P: 9311 5822. M: 041 830 3437.
mailto: scropper at botanicusaustralia.com.au
<mailto:scropper at botanicusaustralia.com.au>
web: www.botanicusaustralia.com.au <http://www.botanicusaustralia.com.au>
Sergio Clark wrote:
> Hi Simon,
>
> You can also take a look to the different map projections on Wikipedia:
> http://en.wikipedia.org/wiki/Map_projection
>
> About your question:
> "... after you project the "natural" locations on the earths curved 3D
> surface to a plane what is the visual 2D representation called? Don't
> say projection. Whats its name?"
>
> For me, this is simply called a "map".
>
>
> Regards,
>
>
> Sergio Clark
> Equipo gvSIG
> IVER T.I., S.A.
> www.iver.es
> www.gvsig.com
>
>
>
> Simon Cropper (Botanicus Australia Pty Ltd) escribió:
>> Ben,
>>
>> Sorry for the persistence, it gets confusing when the same word is
>> used to represent different things. Thanks again.
>>
>> Cheers Simon
>>
>> Simon Cropper
>> Botanicus Australia Pty Ltd
>> PO Box 160, Sunshine, Victoria 3020.
>> P: 9311 5822. M: 041 830 3437.
>> mailto: scropper at botanicusaustralia.com.au
>> <mailto:scropper at botanicusaustralia.com.au>
>> web: www.botanicusaustralia.com.au
>> <http://www.botanicusaustralia.com.au>
>>
>>
>>
>> Benjamin Ducke wrote:
>>
>>> Sorry, but it really is that messy. It gets a bit clearer, when you
>>> think of "geographical projection" as a more specific type of
>>> projection. And yes, the projected location of a point is its
>>> projection -- sorry.
>>>
>>> I like this page a lot:
>>> http://www.asprs.org/resources/grids/
>>>
>>> Lat-long coordinate systems do not need to be projected, as
>>> far as I understand, as they are managed in their natural
>>> representation.
>>>
>>> Ben
>>>
>>>
>>> ----- Original Message -----
>>> From: "Simon Cropper (Botanicus Australia Pty Ltd)"
>>> <scropper at botanicusaustralia.com.au>
>>> To: "Users and Developers mailing list"
>>> <gvsig_internacional at listserv.gva.es>
>>> Sent: Thursday, December 17, 2009 2:18:13 PM GMT +01:00 Amsterdam /
>>> Berlin / Bern / Rome / Stockholm / Vienna
>>> Subject: Re: [Gvsig_english] BUG: gvSIG 1.9 (Build 1253) Image
>>> Filtering
>>>
>>> Ben,
>>>
>>> "Projection = a mathematical formula and its parameters that allows
>>> you to literally
>>> project "natural" locations on the Earth's curved 3D surface to a
>>> plane for display on e.g. a 2D map or monitor. An approximation
>>> model of Earth's geoid shape ("Ellipse") is
>>> also needed for this to work."
>>>
>>> OK... after you project the "natural" locations on the earths curved
>>> 3D surface to a plane what is the visual 2D representation called?
>>> Don't say projection. Whats its name? Are their multiple versions of
>>> this entity (depending on the creator)? How does this relate to
>>> lat-long?
>>> Do you know of a good explanation of the "Datum + Projection + CRS =
>>> SRS" concept on the web (or can you provide one), so I can better
>>> understand the distinction between the various components?
>>>
>>> Cheers Simon
>>>
>>> Simon Cropper
>>> Botanicus Australia Pty Ltd
>>> PO Box 160, Sunshine, Victoria 3020.
>>> P: 9311 5822. M: 041 830 3437.
>>> mailto: scropper at botanicusaustralia.com.au
>>> <mailto:scropper at botanicusaustralia.com.au>
>>> web: www.botanicusaustralia.com.au
>>> <http://www.botanicusaustralia.com.au>
>>>
>>>
>>>
>>> Benjamin Ducke wrote:
>>>
>>>> A projection does just what the name says: it projects points from a
>>>> 3D position on a curved surface to a 2D position on a cartesian
>>>> (orthogonal) coordinate grid.
>>>>
>>>> Datum + Projection + CRS = SRS
>>>>
>>>> However, in most GIS user interfaces: SRS = Projection
>>>>
>>>> Ben
>>>>
>>>> ----- Original Message -----
>>>> From: "Simon Cropper (Botanicus Australia Pty Ltd)"
>>>> <scropper at botanicusaustralia.com.au>
>>>> To: "Users and Developers mailing list"
>>>> <gvsig_internacional at listserv.gva.es>
>>>> Sent: Thursday, December 17, 2009 1:09:58 PM GMT +01:00 Amsterdam /
>>>> Berlin / Bern / Rome / Stockholm / Vienna
>>>> Subject: Re: [Gvsig_english] BUG: gvSIG 1.9 (Build 1253) Image
>>>> Filtering
>>>>
>>>> Ben,
>>>>
>>>> So your definition of projection is limited to the visual 2D
>>>> representation of a 3D sphere. Isn't this a datum-coordinate combo
>>>> as I stated?
>>>>
>>>> Cheers Simon
>>>>
>>>> Simon Cropper
>>>> Botanicus Australia Pty Ltd
>>>> PO Box 160, Sunshine, Victoria 3020.
>>>> P: 9311 5822. M: 041 830 3437.
>>>> mailto: scropper at botanicusaustralia.com.au
>>>> <mailto:scropper at botanicusaustralia.com.au>
>>>> web: www.botanicusaustralia.com.au
>>>> <http://www.botanicusaustralia.com.au>
>>>>
>>>>
>>>>
>>>> Benjamin Ducke wrote:
>>>>
>>>>> And here comes the artillery:
>>>>>
>>>>> Coordinate (reference) system (CRS) = a mathematical convention
>>>>> for describing locations relative
>>>>> to a defined origin (e.g. Cartesian: 100m East, 200m North,
>>>>> Geographic: lat and long).
>>>>>
>>>>> Datum = a precise description of the origin of a geodetic system,
>>>>> nowadays this often includes
>>>>> a mathematical transformation type and its parameters to convert
>>>>> measurements from
>>>>> a foreign system into the system for which the datum is defined
>>>>> (e.g. Potsdam datum).
>>>>>
>>>>> Projection = a mathematical formula and its parameters that allows
>>>>> you to literally
>>>>> project "natural" locations on the Earth's curved 3D surface to a
>>>>> plane for display on e.g. a 2D map or monitor. An approximation
>>>>> model of Earth's geoid shape ("Ellipse") is
>>>>> also needed for this to work.
>>>>>
>>>>> Spatial reference system (SRS) or geodetic reference system: the
>>>>> whole bunch of those
>>>>> components together. This is what a GIS menu entry usually refers
>>>>> to, even if it is
>>>>> labelled "projection".
>>>>>
>>>>> ... never mind what the GUIs tell you!
>>>>>
>>>>> Ben
>>>>>
>>>>>
>>>>> ----- Original Message -----
>>>>> From: "Simon Cropper (Botanicus Australia Pty Ltd)"
>>>>> <scropper at botanicusaustralia.com.au>
>>>>> To: "Users and Developers mailing list"
>>>>> <gvsig_internacional at listserv.gva.es>
>>>>> Sent: Thursday, December 17, 2009 12:49:06 PM GMT +01:00 Amsterdam
>>>>> / Berlin / Bern / Rome / Stockholm / Vienna
>>>>> Subject: Re: [Gvsig_english] BUG: gvSIG 1.9 (Build 1253) Image
>>>>> Filtering
>>>>>
>>>>> Ben & Sergio,
>>>>>
>>>>> Thanks for your understanding. Feel a bit stupid now I look at the
>>>>> dialog box. Pretty obvious when you have your head in gear.
>>>>>
>>>>> Ben. I'll bite. Enlighten me on the distinction between projection
>>>>> & coordinate system.
>>>>>
>>>>> OK, here I go again, potentially making myself look stupid...
>>>>>
>>>>> coordinate system = northing-easting, lat-long (MGA55, AMG53)
>>>>> datum = framework used to reference the coordinate system (GDA94,
>>>>> AGD66)
>>>>> projection = particular datum-coordinate system combo (e.g. GDA94
>>>>> MGA55, GDA94 lat/long, AGD66 AMG53, etc)
>>>>>
>>>>> Should I duck for cover?
>>>>>
>>>>> Cheers Simon
>>>>>
>>>>> Simon Cropper
>>>>> Botanicus Australia Pty Ltd
>>>>> PO Box 160, Sunshine, Victoria 3020.
>>>>> P: 9311 5822. M: 041 830 3437.
>>>>> mailto: scropper at botanicusaustralia.com.au
>>>>> <mailto:scropper at botanicusaustralia.com.au>
>>>>> web: www.botanicusaustralia.com.au
>>>>> <http://www.botanicusaustralia.com.au>
>>>>>
>>>>>
>>>>>
>>>>> Benjamin Ducke wrote:
>>>>>
>>>>>> It's OK Simon, we forgive you now ;)
>>>>>>
>>>>>> The problem with GIS is that the user interfaces are often designed
>>>>>> by people who are not actually cartographers or geoscientists.
>>>>>> Let's not even get started about the way the terms "projection"
>>>>>> or "coordinate system" are used in GIS...
>>>>>>
>>>>>> Ben
>>>>>>
>>>>>> ----- Original Message -----
>>>>>> From: "Simon Cropper (Botanicus Australia Pty Ltd)"
>>>>>> <scropper at botanicusaustralia.com.au>
>>>>>> To: "Users and Developers mailing list"
>>>>>> <gvsig_internacional at listserv.gva.es>
>>>>>> Sent: Thursday, December 17, 2009 12:16:47 PM GMT +01:00
>>>>>> Amsterdam / Berlin / Bern / Rome / Stockholm / Vienna
>>>>>> Subject: Re: [Gvsig_english] BUG: gvSIG 1.9 (Build 1253) Image
>>>>>> Filtering
>>>>>>
>>>>>> Ben,
>>>>>>
>>>>>> I agree. In cartographic terms it is correct. It should stay that
>>>>>> way, but as you stated other packages don't express these ranges
>>>>>> correctly and newbies to gvSIG, like myself, misunderstand the
>>>>>> dialog box and post a thread. Some sort of reminder or warning
>>>>>> right next to the input box would be a timely reminder.
>>>>>>
>>>>>> Cheers Simon
>>>>>>
>>>>>> Simon Cropper
>>>>>> Botanicus Australia Pty Ltd
>>>>>> PO Box 160, Sunshine, Victoria 3020.
>>>>>> P: 9311 5822. M: 041 830 3437.
>>>>>> mailto: scropper at botanicusaustralia.com.au
>>>>>> <mailto:scropper at botanicusaustralia.com.au>
>>>>>> web: www.botanicusaustralia.com.au
>>>>>> <http://www.botanicusaustralia.com.au>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Benjamin Ducke wrote:
>>>>>>
>>>>>>> Please keep it that way. It's perfectly correct in cartographic
>>>>>>> terms. The fact that all other GIS have taught their users wrong
>>>>>>> terminology does not change that.
>>>>>>>
>>>>>>> Ben
>>>>>>>
>>>>>>> ----- Original Message -----
>>>>>>> From: "Sergio Clark" <sergio.clark at iver.es>
>>>>>>> To: "Users and Developers mailing list"
>>>>>>> <gvsig_internacional at listserv.gva.es>
>>>>>>> Sent: Thursday, December 17, 2009 9:58:23 AM GMT +01:00
>>>>>>> Amsterdam / Berlin / Bern / Rome / Stockholm / Vienna
>>>>>>> Subject: Re: [Gvsig_english] BUG: gvSIG 1.9 (Build 1253) Image
>>>>>>> Filtering
>>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> I don't think this is a bug. Now both raster and vector layers
>>>>>>> work the same way regarding the scale range of visualization (we
>>>>>>> homogenized the text in both pannels inside 'Properties').
>>>>>>>
>>>>>>> I mean, "Don't show layer when the scale is greater than 1:100"
>>>>>>> means that it won't be displayed when scale is 1:99, because
>>>>>>> second one is "greater scale" than first one (minor denominator,
>>>>>>> but major scale). And it's the same for "less than...".
>>>>>>>
>>>>>>> Regards,
>>>>>>> Sergio.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Sergio Clark
>>>>>>> Equipo gvSIG
>>>>>>> IVER T.I., S.A.
>>>>>>> www.iver.es
>>>>>>> www.gvsig.com
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Rahkonen Jukka escribió:
>>>>>>>
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> Maybe this is the old question about which scale is big and
>>>>>>>> which is
>>>>>>>> small? Compare scales 1:10 and 1:100. Hundred is bigger number
>>>>>>>> than ten,
>>>>>>>> but because it appears in the denominator the scale 1:100 is
>>>>>>>> smaller
>>>>>>>> than 1:10.
>>>>>>>>
>>>>>>>> Perhaps it would be more clear to put the words in another way:
>>>>>>>> "Do not
>>>>>>>> show this layer if scale denominator is bigger/smaller than".
>>>>>>>>
>>>>>>>> -Jukka Rahkonen-
>>>>>>>>
>>>>>>>> Simon Cropper wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>> Hi Guys,
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>> I have Noted a bug in the program.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>> If you set the scale range for a raster file the "is above
>>>>>>>>> 1:????" and
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>> "is below 1:????" is around the wrong way.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>> If you set "Do not show this layer if the scale is above
>>>>>>>>> 1:100000",
>>>>>>>>>
>>>>>>>>>
>>>>>>>> the
>>>>>>>>> image only appears if the scale exceeds 1:100,000.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>> So either the text is wrong or the filter condition is around the
>>>>>>>>>
>>>>>>>>>
>>>>>>>> wrong way.
>>>>>>>> _______________________________________________
>>>>>>>> Gvsig_internacional mailing list
>>>>>>>> Gvsig_internacional at listserv.gva.es
>>>>>>>> http://listserv.gva.es/cgi-bin/mailman/listinfo/gvsig_internacional
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
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