Re: [mapnik] Looking for Mapnik/GDAL Coach

[Andrew Harvey]

On 24/10/12 10:12, Scott Vanderbilt wrote:
> Hello.
>
> Briefly, I would like to find an expert who can coach me through the
> process of building a set of terrain tiles. I'd like to start off with an
> initial phone conversation, with follow-ups via email or phone when
> necessary. I'm willing to pay for this support. Please quote your rate.
>
> More detail: I'm trying to build a set of very clean, high
> resolution terrain tiles for the island of Britain. Think of the Google
> terrain layer without roads and place names. I'm starting with a set of
> 50-meter DEM data in NTF and ASC format. I have successfully created color
> relief, hill shade, and slope shade GeoTIFFs from these data using GDAL. As
> further source data, I also have shapefiles for coastline, geographic
> boundary, and water features, as well as DXF files for contour lines. I
> will not be including roads, administrative boundaries, forestry, or any
> other data in these tiles. I want ultimately end up with tile sets for zoom
> levels 4 through 14, with as high a resolution as can be squeezed out of
> the source data.
>
> I have been able to produce one large map that is close to what I want to
> end up with, but I'm not very happy with the end results. The render times
> are very slow when clipping the GeoTIFFs. I'm also unhappy with the
> resolution when viewing the map fully zoomed in. There's major room for
> improvement.
>
> This is my first experience making map tiles (obviously), and I'm certain
> there are more efficient ways to go about it, as well as ways to improve
> the results. But most importantly, I'm in a hurry, and don't have time to
> fumble through this process with the usual support channels. I'm looking
> for someone who can set me down the right path quickly, answer questions as
> they come up, and QA my work. Telephone conversations or real-time chat
> would be best, at least some of the time. Email and other high-latency
> channels are suboptimal.
>
> I hope I'm not being too demanding. I'm really not. Just short on time. :-)

You may find it helpful to take a look at

https://github.com/andrewharvey/srtm3-stylesheets

I have a process for creating a hypsometric tinted shaded relief contour
map.

[Dane Springmeyer]

On Oct 23, 2012, at 4:12 PM, Scott Vanderbilt wrote:

I have been able to produce one large map that is close to what I want to end up with, but I'm not very happy with the end results. The render times are very slow when clipping the GeoTIFFs. I'm also unhappy with the resolution when viewing the map fully zoomed in. There's major room for improvement.

Hi Scott,

Hopefully you've heard from someone that can provide the level of quick support you need. I'll just add:

1) If your geotiff rendering is slow, it may be because you are missing overviews. You can generate these with the `gdaladdo` tool. And then you should use the Mapnik "GDAL" datasource plugin to read the rasters.

2) In terms of "resolution" it sounds like when you zoom into z13-14 you start to see pixelation in the rasters? Is that what you mean? If so, you may wish to apply bilinear scaling (or a higher quality filter like bicubic, lanczos, or gaussian ) to your RasterSymbolizer. This will blur the data slightly, which can help the look. Then, with Mapnik >= 2.1 you can then apply a "sharpen" image filter to get the raster looking crisp again.

Dane

[Fernando]

On 28/10/12 23:11, Scott Vanderbilt wrote:
>
>
> With respect to image filters, I don't see much in the way of
> documentation of these in the mapnik wiki. In fact, other than being
> mentioned in 2.1 release notes, I can't find anything at all. Where
> can I find docs and/or examples of how image filters are applied?
> Perhaps I am not looking hard enough. FWIW, I am using the XML interface.
>

This may help you:
http://mapbox.com/tilemill/docs/guides/comp-op/

Fernando.

[Dane Springmeyer]

On Oct 28, 2012, at 7:11 PM, Scott Vanderbilt wrote:

On Friday, October 26, 2012 11:58:41 AM UTC-7, Dane Springmeyer wrote:

2) In terms of "resolution" it sounds like when you zoom into z13-14 you start to see pixelation in the rasters? Is that what you mean? If so, you may wish to apply bilinear scaling (or a higher quality filter like bicubic, lanczos, or gaussian ) to your RasterSymbolizer. This will blur the data slightly, which can help the look. Then, with Mapnik >= 2.1 you can then apply a "sharpen" image filter to get the raster looking crisp again.

Dane:

Thanks very much for that.

I was using bilinear scaling to begin with on all three elevation layers (color relief, hill shade, and slope shade), but I will try the others to see whether they improve the results.

Okay, keep in mind that the default is `scaling="near"` and bilinear will be slower, so don't use it unless it helps the look you are going for.

With respect to image filters, I don't see much in the way of documentation of these in the mapnik wiki. In fact, other than being mentioned in 2.1 release notes, I can't find anything at all. Where can I find docs and/or examples of how image filters are applied? Perhaps I am not looking hard enough. FWIW, I am using the XML interface.

Yeah, we need to do a docs on them still. In the meantime try:

<Style image-filters="sharpen" />

...

</Style

Thanks again.

- Scott