How to determine the scale

[Ramesh Karra]

Ed,

I really appreciate your quick responses.
I have looked at the tutorial and used 'cs2cs' to get new extent values
and used output projection as shown below

PROJECTION
  "init=epsg:2163"
END

but I am getting the following error -

"loadMapInternal(): General error message. Given map extent is invalid."

The coordinates that I am using represent a part of India. I am not sure
if the parameters I passed to 'cs2cs' to calculate the new extent are
valid for india. I have used the exact same parameters as mentioned on the
website -

cs2cs +proj=latlong +datum=WGS84 +to +proj=laea +ellps=clrk66 +lat_0=45
+lon_0=-100

Also I am not sure if I can use epsg code 2163 for india.
I am supposed to find out the correct code by looking at the proj/nad/epsg
file? There are so many entries for India and I am not sure which one to
use.


Thanks
Ramesh


On Thu, 23 Feb 2006 16:53:21 -0500, Ed McNierney <ed at TOPOZONE.COM> wrote:

>Ramesh -
>
>MapServer will do all the reprojection for you.  You do not need to
>convert your source data.  You simply specify the input projection
>(lat/lon) for your input data and the output projection (LAEA) for the
>map image.
>
>To get started, use the MapServer Tutorial at
>http://mapserver.gis.umn.edu/docs/tutorial/tutorial - there's a section
>there on getting started with projections in MapServer.
>
> - Ed
>
>Ed McNierney
>President and Chief Mapmaker
>TopoZone.com / Maps a la carte, Inc.
>73 Princeton Street, Suite 305
>North Chelmsford, MA  01863
>ed at topozone.com
>(978) 251-4242
>
>-----Original Message-----
>From: Ramesh Karra [mailto:karrarm at YAHOO.COM]
>Sent: Thursday, February 23, 2006 4:49 PM
>To: MAPSERVER-USERS at LISTS.UMN.EDU; Ed McNierney
>Subject: Re: How to determine the scale
>
>Thanks Ed,
>
>Thank you very much for the quick response. How do I convert my lat/long
>to a different projection, say LAEA? When I do this conversion, all my
>shape files need to be re-created with this new projection co-ordinates,
>right?
>I have searched on the web, but could not figure out a way to convert
>lat/long to LAEA. I really appreciate any pointers related to this.
>
>Thanks
>Krishna
>
>On Thu, 23 Feb 2006 15:38:50 -0500, Ed McNierney <ed at TOPOZONE.COM>
>wrote:
>
>>Ramesh -
>>
>>If your output map image is in a "lat/long" projection - which yours
>>seems to be, since the extents are in degrees - then you really cannot
>>put a scale bar on the map.  Distances are not constant across such a
>>map, and depend on the latitude and the orientation of the line you're
>>measuring.  A one-degree North/South line is not the same length as a
>>one-degree East/West line (except if you're near the equator).
>>
>>If you want to put a usable scalebar on your map, measured in meters or
>
>>miles, etc., you need to use a different output projection - one that
>>is designed to provide such measurements.
>>
>> - Ed
>>
>>Ed McNierney
>>President and Chief Mapmaker
>>TopoZone.com / Maps a la carte, Inc.
>>73 Princeton Street, Suite 305
>>North Chelmsford, MA  01863
>>ed at topozone.com
>>(978) 251-4242
>>
>>-----Original Message-----
>>From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU]
>>On Behalf Of Ramesh Karra
>>Sent: Thursday, February 23, 2006 3:26 PM
>>To: MAPSERVER-USERS at LISTS.UMN.EDU
>>Subject: [UMN_MAPSERVER-USERS] How to determine the scale
>>
>>Hi,
>>
>>I have a map file with extent "74.3605 24.2590 79.5400 20.5070". I have
>
>>a layer(with data in a shape file) with very few points
>>
>>75.23478 23.40182
>>75.78261 21.90126
>>76.37162 22.90461
>>77.32890 20.88712
>>
>>The mapserver shows these points correctly. But it does not have
>>correct idea about the distance between the points. How do I indicate
>>the mapserver that these are latitude and longitudes and the distances
>>should be calculated correctly? Do I need to use scale? or some other
>>projection?
>>
>>I really appreciate any help in this regard.
>>
>>Thanks,
>>Ramesh