From the point of view GIS professionals this question will be sure very primitive, but please keep in mind - i'm totally newbie in this area - and this is my 1st question here.
Have several GPS coordinates and need draw them as pins the into world-map image. On the internet i found one "public domain" image of the world. (attached a resized smaller version here - in reality I need 2000 pixel wide image).
I know perl - so, decided to use:
- GD.pm (or Image::Magick) - for graphics operations
- and installed the Geo::Proj4 perl module to cartographic conversions.
The manual says:
Perform a forward projection from LATITUDE and LONGITUDE (LL) to the cartographic projection (XY) represented by the Geo::Proj4 instance
Returned are two values, usually X and Y in meters, or whatever units are relevant to the given projection
If I understand right - that is enough for me, need only convert the meters to my pixels in my map image.
For using the above
forward routine, it need an $proj instance what must define the map projection TYPE, like:
$proj = Geo::Proj4->new(proj => "merc", ellps => "clrk66", lon_0 => -96); #or my $proj = Geo::Proj4->new(init => "epsg:28992"); #and like (many-many-many possibilities).
As the manual says - It is not easy. :(
The object defines the target projection, but that's easier said than done: projections have different parameter needs. The parameters which can (or need to) be used are listed with cs2cs -lP. The manual page of cs2cs explains how the configuration works.
Now the questions:
- In what projection is the attached map? - or how to determine it?
- How i can decide how to initialize the Proj4 instance for this image?
- I'm totally lost how to continue - the
cs2cs -lP.returns me approx 150 different projections :(
- if this image is not usable - is here some better way to get an better defined map? Because need generate many-many-many bitmap images, can't use google API or like)
Thank you for a patience.