[Proj] Lambert projection with one or two standard parallels and proj4

[Hermann Peifer]

A few additional remarks:

- add +no_defs to your first example in order to avoid unwanted default 
values

- about this part: +a=6367470 +b=6367470 +ellps=sphere +datum=WGS84

+datum=WGS84 is a shorthand for: +ellps=WGS84 +towgs84=0,0,0. You 
already have +ellps=sphere. Your reference surface cannot be a shpere 
and the WGS84 ellipsoid at the same time. As you already have +a=6367470 
and +b=6367470, you should drop both +ellps=sphere and +datum=WGS84

- in case of doubts, use cs2cs -v for more info about which parameters 
are actually takes, and which are ignored

Hermann


On 2013-04-25 6:45, Charles Karney wrote:
> The default values of lat_1 and lat_2 are 33 and 45, so in your first
> example you had +lat_1=46.244 +lat_2=45 which is not what you intended.
> The second example does what you wanted.
>
>     --Charles
>
> On 04/25/2013 03:51 AM, Linton Corbet wrote:
>> Hello all,
>>
>> I'm sure there is a gap in my understanding, but I haven't been able to
>> identify where it is, nor how to fill it. My issue is this:
>>
>> I'm transforming lon lat coordinates into a lambert conformal conic
>> projection.
>>
>> The lambert projection uses a single standard parallel 46.244 and the
>> central meridian is 17.0. And it's on a sphere, but that's not
>> particularly relevant here. I am using packages that use the proj4 library.
>>
>> I test the transformation using linux tool cs2cs as follows:
>>
>> echo "15.220483 48.437298" | cs2cs +proj=lonlat +to +proj=lcc
>> +lat_1=46.244 +lat_0=46.244 +lon_0=17. +a=6367470 +b=6367470
>> +ellps=sphere +datum=WGS84
>>
>> -131346.80 245318.16
>>
>> I also understand that the one-standard parallel form is the same as the
>> two-standard parallel form if the two standard parallels are the same.
>> It is more convenient for me to give all parallels in my scripts - let
>> proj do the work. So I also test with:
>>
>> echo "15.220483 48.437298" | cs2cs +proj=lonlat +to +proj=lcc
>> +lat_1=46.244 +lat_2=46.244 +lat_0=46.244 +lon_0=17. +a=6367470
>> +b=6367470 +ellps=sphere +datum=WGS84
>>
>> -131290.66 245281.34
>>
>> yet I get different results. Any ideas as to why?
>>
>> And at very least, what am I doing wrong and which approach should I use?
>>
>> Kind regards,
>> Linton Corbet
>>
>>
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>
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