[mapserver-users] Changing the "EXTENT" for a layer

Wed Feb 25 06:37:12 PST 2009

Hi, 

There is no need to guess this, nor would it be very useful.  Instead, insert DEBUG 5 into your layer definitions, collect log and see from the timing values how it goes.  Make a pre-reproprojected layer from your data with ogr2ogr program, do some timings and compare the results.

-Jukka-

________________________________

Lähettäjä: Adrian Popa [mailto:adrian_gh.popa at romtelecom.ro] 
Lähetetty: 25. helmikuuta 2009 14:53
Vastaanottaja: Rahkonen Jukka
Kopio: mapserver-users at lists.osgeo.org
Aihe: Re: [mapserver-users] Changing the "EXTENT" for a layer

	Yup, it worked like a charm!

	Thank you for your help. One more question - how cpu intensive is reprojection using mapserver? I mean, if I have 300 users requesting the page, will I kill the CPU because it needs to reproject a layer, or are the calculations straight-forward and add little extra load on the server? 
	Can I reproject the layer "offline" and load it without projection in mapserver? If I can, which tool would I use (proj4?)?

	Thanks again,
	Adrian

	Rahkonen Jukka wrote: 

		Hi,

		Mapserver works without any knowledge about projection with one dataset if only the extents suit the data coordinates. That's the case with your ESRI layer. But you have two datasets which obviously are using different projections.  To show them together either (or both) of them needs to be reprojected.  And that is possible only if you know and tell Mapserver the projections for both datasets.

		What needs to be done is
		1) Set at the MAP level the projection that you want Mapserver to use for output as well as map extents using values and units of the output projection.
		2) Set at the LAYER level the projections for both of the datasets.

		To make is as simple as possible for the beginning I suggest to use projection epsg:4326 and a bit wider extents than you have now at MAP level.  Thats because those extents are already working for you, and ESRI dataset most propably is in WGS84 projection.  Thus you should use projection epsg:4326 also for your ESRI layer.

		Then there will be just the Mapinfo layer left.  Defined by the the ogrinfo line PARAMETER["central_meridian",27] and coordinates it looks like it might be in UTM 35N projection (epsg:32635).  Have a try with that first.

		-Jukka Rahkonen-

________________________________

		L�hett�j�: mapserver-users-bounces at lists.osgeo.org [mailto:mapserver-users-bounces at lists.osgeo.org] Puolesta Adrian Popa
		L�hetetty: 25. helmikuuta 2009 9:25
		Vastaanottaja: mapserver-users at lists.osgeo.org
		Aihe: [mapserver-users] Changing the "EXTENT" for a layer

			Hello all!

			I'm trying to display some layers (ESRI Shapefile and MapInfo) in the same map. The ESRI shapefiles work just fine, and I've used them for a long time. The new MapInfo layer however has very different "Extent" values for its coordinates and does not overlap with the original layers (they should overlap, because they cover the same area).

			Here is some output from ogrinfo:

			1. A layer that displays ok and for which the coordinates are longitude/latitude:

			[adrianp at server data]$ ogrinfo Limits.shp -so -al
			Had to open data source read-only.
			INFO: Open of `Limits.shp'
			      using driver `ESRI Shapefile' successful.

			Layer name: Limits
			Geometry: Line String
			Feature Count: 8718
			Extent: (20.261522, 43.618437) - (29.704897, 48.264780)
			Layer SRS WKT:
			GEOGCS["GCS_WGS_1984",
			    DATUM["WGS_1984",
			        SPHEROID["WGS_1984",6378137.0,298.257223563]],
			    PRIMEM["Greenwich",0.0],
			    UNIT["Degree",0.0174532925199433]]
			OBJECTID_1: Integer (9.0)
			TIP: Integer (4.0)
			Shape_Leng: Real (19.11)

			2. A layer which displays if I set the Extent parameter in the MAP file to the values returned by ogrinfo:

			[adrianp at server data]$ ogrinfo coverage.TAB -so -al
			Had to open data source read-only.
			INFO: Open of `coverage.TAB'
			      using driver `MapInfo File' successful.

			Layer name: coverage
			Geometry: Unknown (any)
			Feature Count: 1
			Extent: (550.002594, 4830850.004496) - (707800.001127, 5318099.996174)
			Layer SRS WKT:
			PROJCS["unnamed",
			    GEOGCS["unnamed",
			        DATUM["WGS_1984",
			            SPHEROID["WGS 84",6378137,298.257223563],
			            TOWGS84[0,0,0,-0,-0,-0,0]],
			        PRIMEM["Greenwich",0],
			        UNIT["degree",0.0174532925199433]],
			    PROJECTION["Transverse_Mercator"],
			    PARAMETER["latitude_of_origin",0],
			    PARAMETER["central_meridian",27],
			    PARAMETER["scale_factor",0.9996],
			    PARAMETER["false_easting",500000],
			    PARAMETER["false_northing",0],
			    UNIT["Meter",1.0]]
			LEGEND: String (50.0)
			THRESHOLD: Real (0.0)
			COLOR: String (20.0)
			Prediction_name: String (50.0)

			I don't know how the second layer was generated (perhaps the values in extent are not longitude/latitude values), but I would like to display both layers in the same coordinate system.
			If I consider the second set of values is longitude/latitude, they make no sense (unless the surface of Earth is the same as the surface of Jupiter!).

			My question is: can mapserver do the translation of coordinates (by adding/substracting a fixed value), or do I need to do this with another system?
			If the solution is external to mapserver, what's my next step (some manuals please!)?

			I haven't worked with projections; could this be the cause?

			Any help is appreciated, thanks!
			Adrian

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