artifacts at tiled image borders

[Dylan Beaudette]

Ed,

Thanks for  the input.

Well, I actually have about 3,000 or more of them, at least enough to cover 
most of CA. Once we add NV and AZ, there are going to be a lot more.

Since the DOQQ have a tremendous amount of overlap, i have been toying with 
the idea of merging the 4 quarter quads back into a single quad- potentially 
saving some space. 

I don't really need or want imagery that is much greater than 3m res, in fact 
5 meter might be enough... the 10 meter downsampling has just resulted in 
images that are a bit too poor quality. 

Finally, if JPEG is a poorly performing image format, at the expense of some 
extra hard disk space, perhaps staying with geotiff is the thing to do..

any thoughts?

thanks!

Dylan

On Wednesday 27 July 2005 02:43 pm, Ed McNierney wrote:
> Dylan -
>
> In addition to Frank's accurate description of the problem, I'll also
> note that JPEG is a very poorly-performing format for geospatial
> applications.  Yes, you do lose something if you want to save space!
>
> How many DOQQs do you need to deal with?  They're big, but they're not
> THAT big.
>
> 	- Ed
>
> Ed McNierney
> President and Chief Mapmaker
> TopoZone.com / Maps a la carte, Inc.
> 73 Princeton Street, Suite 305
> North Chelmsford, MA  01863
> Phone: +1 (978) 251-4242
> Fax: +1 (978) 251-1396
> ed at topozone.com
>
> -----Original Message-----
> From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
> Behalf Of Dylan Beaudette
> Sent: Wednesday, July 27, 2005 4:56 PM
> To: MAPSERVER-USERS at LISTS.UMN.EDU
> Subject: [UMN_MAPSERVER-USERS] artifacts at tiled image borders
>
> Greetings,
>
> I have been doing some research on better ways to store my aerial
> imagery, so that I can keep a higher resolution version of my source
> files. Until now I have been downsampling USGS DOQQ images from 1 meter
> resolution to 10 meters, saving the result as a geoTiff. With overviews,
> these file are about 1.5 mb per quarter quad. A shapefile tile index is
> used to render the images in Mapserver.
>
> Last night I re-created a section of the tiled dataset in JPEG format at
> 3 meter resolution. I am much happier with the resulting increase in
> detail, however I am now noticing some strange artifacts showing up at
> the "seams" of the tile index.
>
> here is an example of what I am talking about:
> http://169.237.35.250/~dylan/temp/mapserver/bad_edges.jpg
>
> the source data do not appear to have these type of "rough edges":
> http://169.237.35.250/~dylan/temp/mapserver/original_clean_edges.jpg
>
> I am using the OFFSITE operator in my map file to ignore pixels with an
> RGB value of '0 0 0'.
>
> Does anyone have any idea what could be causing these rough looking
> seams at the tileindex boundaries?
>
> thanks in advance!
>
>
> --
> Dylan Beaudette
> Soils and Biogeochemistry Graduate Group University of California at
> Davis
> 530.754.7341

-- 
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341