[Proj4j] Question About Valid CRS Identifiers To Get Started With GUI Development

[Sunburned Surveyor]

Martin,

I'm finally getting some time after work today to look at the GUI
design issues we discussed a little closer. I have some more questions
that I was hoping you could help me with.

Martin wrote: "CRS IDs - the PROJ4 archive of CRSes is in the /nad directory, in
various files called "epsg", "esri", etc."

(1) What does "nad" stand for? Does the current proj4j library support
all 5 different CRS definition formats (epsd, esri, nad27, nad83,
world)?

Martin wrote: "I'm taking the file name as
the Authority code.  Each file contains comments, and CRS definitions
which look like:

<id> proj4 spec string

So createFromName takes a CRS name which looks like eg "EPSG:1234" and
looks up that CRS in the EPSG file.  (I will add all this to the
javadoc...)"

Martin also wrote: "One thing that would be VERY nice is to be able to
capture the CRS
descriptions which are typically in the comment immediately before the
CRS spec.  This should be a fairly simply amendment to the parser."

(2) I noticed the epsg file (as an example) has two elements for each
CRS that could potentially be used to identify the CRS to the user.
The first is the integer code. The second is a more user friendly name
included as the comment. I think I will need to display both in the
list box to make the GUI useful to the user. Is the number sign used
to mark other types of comments in the NAD files, or just these user
friendly CRS identifiers? I want to make sure I can depend on the user
friendly CRS identifier following immediately after the number sign.
(Or we could add a tag after the number sign for those user friendly
identifiers so I will know when I find them.)

Martin wrote: "Now, the current file parser just extracts a single CRS
from the file.
 It does parse the entire file tho, so could easily be extended to
extract all of them."

When you say "current file parser" do you mean the Proj4FileReader
class? I took a look at the source code for that class today. The
readFile method looks pretty scary. Do you want me to add the
functionality I need to extract CRS identifiers from the NAD files to
that class or to a different class? I'm thinking of two methods like:

public List<String> getFormalCRSIdentifiers()
public List<String> getFriendlyCRSIdentifiers()

I can also see a need for two methods like:

public String getFormalCRSIdentifierForFriendlyCRSIdentifier()
public String getFriendlyCRSIdentifierForFormalCRSIdentifier()

But those could be put into a utility class. Do you want to package
the authority code, formal identifier, and friendly identifier in its
own CrsIdentifier class, or is that getting two complicated? We could
start using the CrsIdentifier class in the GUI and then use it later
in the rest of the library if desired.

I've got some things I can start on while I wait for these answers.
I'm going to create a new package named org.osgeo.proj4j.gui. I won't
commit this until I get your permission. Do you want me working on my
GUI stuff in the trunk of the SVN or in a new branch?

Thanks,

Landon

On Mon, Feb 8, 2010 at 8:56 AM, Martin Davis <mtnclimb at gmail.com> wrote:
> Landon,
>
> Your note contains lots of subthreads!  Here goes with my thoughts:
>
> * CRS IDs - the PROJ4 archive of CRSes is in the /nad directory, in
> various files called "epsg", "esri", etc.  I'm taking the file name as
> the Authority code.  Each file contains comments, and CRS definitions
> which look like:
>
> <id> proj4 spec string
>
> So createFromName takes a CRS name which looks like eg "EPSG:1234" and
> looks up that CRS in the EPSG file.  (I will add all this to the
> javadoc...)
>
> Now, the current file parser just extracts a single CRS from the file.
>  It does parse the entire file tho, so could easily be extended to
> extract all of them.
>
> One thing that would be VERY nice is to be able to capture the CRS
> descriptions which are typically in the comment immediately before the
> CRS spec.  This should be a fairly simply amendment to the parser.
>
> * I agree with your proposed design for the UI - that's pretty much
> what I was thinking too.  Shapefile support would be great, and it
> makes sense to use the GeoTools code.  I was also thinking of
> providing a text box to allow a user to directly enter a coordinate,
> too.
>
> * The MetaCRS test parser is pretty much done.  Have a look at
> MetaCRSTestCmd. java.
>
> * One thing that would be nifty is if the GUI would also accept a
> MetaCRS test file, and run all the tests in it.  Something like the
> JUnit runner in Eclipse.  A nice display of all tests and their status
> would be great.
>
> This could even turn into a full-blown MetaCRS test file editor...  !
> That wouild be a great tool to promote the concept.
>
> * I'm still keen on reviving Jerry's great visual display of
> coordinate projections on a world map.  I did ask for the code, but
> haven't got anything so far.  Shouldn't be too hard to reproduce it
> though.
>
> Martin
>
>
> On Fri, Feb 5, 2010 at 4:05 PM, Sunburned Surveyor
> <sunburned.surveyor at gmail.com> wrote:
>> Martin,
>>
>> I was looking over the example code you sent me a few weeks ago. This
>> led me to a question that I want to ask about Proj4J. The answers will
>> help me get started with the GUI development.
>>
>> I see that we pass the CoordinateSystemFactory.createFromName method
>> some type of identifier to obtain a coordinate system. Is there a
>> mechanism within Proj4J that I can use to obtain a list of valid
>> identifiers? I know this information may be embedded in some text
>> files or configuration files. That is fine. I can write a parser if
>> needed to obtain the list if you can point me in the correct place to
>> look. I want to present the user with a list box of valid CRS
>> identifiers. (Actually, I will need two (2) list boxes. One will be
>> for the source CRS and one will be for the desination CRS.)
>>
>> Once I get this figured out, I think the rest will come together
>> without too much of your help. I think I will need to build some
>> wrapper layers that extract ProjCoordinate objects from feature
>> geometries stored in a Shapefile. I imagine transformation of
>> Shapefiles will be our typical use case. Of course, people could want
>> to transform spatial data from other sources too, but I want to get
>> something working with Shapefiles first.
>>
>> So it looks like I will have to layers to implement. One will be the
>> actual GUI, the second will be a layer that reads and writes
>> ProjCoordinate objects from feature geometries in different formats,
>> like ESRI shapefiles. I'm thinking I will tap the GeoTools library for
>> Shapefile support at this point.
>>
>> Let me know what your thoughts are on this.
>>
>> It may take me a few weeks to get a working GUI for Shapefile
>> conversion. After this is done I will work on the parser for the
>> MetaCRS test data.
>>
>> The Sunburned Surveyor
>> _______________________________________________
>> Proj4j mailing list
>> Proj4j at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/proj4j
>>
>