[MapServer-users] Distinguish between pixels outside of SCALE range and nodata pixels

[Mallinger, Bernhard]

Hi,

My nodata value is 0, so I think following your suggestion I can get the
desired effect with just this:

PROCESSING "LUT=1:1,10:1,20:255"

The initial tests look very promising, it seems that it's really possible
to replace SCALE with this LUT directive.

Thanks a lot for your help! So no code change seems to be needed after all.

Best regards,
Bernhard

On Mon, Nov 28, 2022 at 6:24 PM Rahkonen Jukka <
jukka.rahkonen at maanmittauslaitos.fi> wrote:

> Hi,
>
>
>
> What is your nodata value and the datatype of the source raster? If you
> deal with byte or int16 data and the nodata value is 0, you can keep it
> unaltered in your LUT, then map values 1-9 into 1 that is almost black,
> range 10-19 as you wish, and 20 and above into white.
>
>
>
> -Jukka Rahkonen-
>
>
>
> *Lähettäjä:* Mallinger, Bernhard <bernhard.mallinger at eox.at>
> *Lähetetty:* maanantai 28. marraskuuta 2022 16.53
> *Vastaanottaja:* Rahkonen Jukka <jukka.rahkonen at maanmittauslaitos.fi>
> *Kopio:* mapserver-users at lists.osgeo.org
> *Aihe:* Re: [MapServer-users] Distinguish between pixels outside of SCALE
> range and nodata pixels
>
>
>
> Thank you for the suggestion, I have tried it now.
>
> Since the values below the minimum scale is mapped to 0, i tried using the
> following instruction:
>
> PROCESSING "LUT=0:1"
>
> This actually maps the values below the minimum to 1, but also the no data
> values. Do you know if there's a way where I can distinguish between those
> two using LUT?
>
> Best,
>
> Bernhard
>
>
>
>
>
> On Mon, Nov 28, 2022 at 3:26 PM Rahkonen Jukka <
> jukka.rahkonen at maanmittauslaitos.fi> wrote:
>
> Hi,
>
>
>
> Have you tried the LUT processing option
> https://mapserver.org/input/raster.html
> <https://eur06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmapserver.org%2Finput%2Fraster.html&data=05%7C01%7Cjukka.rahkonen%40maanmittauslaitos.fi%7C046212920572444ef6f008dad1504c07%7Cc4f8a63255804a1c92371d5a571b71fa%7C0%7C0%7C638052440048006207%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=hvl4h66%2BfJZhlIiyZKx10SqqwPXyFdyfIZgEooRMqjY%3D&reserved=0>
> ?
>
>
>
> -Jukka Rahkonen-
>
>
>
> *Lähettäjä:* MapServer-users <mapserver-users-bounces at lists.osgeo.org> *Puolesta
> *Mallinger, Bernhard
> *Lähetetty:* maanantai 28. marraskuuta 2022 15.35
> *Vastaanottaja:* mapserver-users at lists.osgeo.org
> *Aihe:* [MapServer-users] Distinguish between pixels outside of SCALE
> range and nodata pixels
>
>
>
> Hello,
>
> We have maps where we want the color scale go from e.g. 10 to 20, so we
> are using this directive:
>
>
> PROCESSING "SCALE_1=10.0,20.0"
>
> This works great by itself, however it also means that pixels with values
> of e.g. 5 are rendered as transparent, which is the same as the nodata
> pixels. So in the final image, you can't tell if data is present but the
> values are too low, or if there just isn't any data.
>
> So the behaviour we would like is that values below 10 are rendered as
> black and values over 20 are rendered as white.
>
> Is this somehow possible with mapscript?
>
>
> We tried to have a look in the source code, and there is this line, which
> effectively assigns 0 to pixels below the minimum:
> https://github.com/MapServer/MapServer/blob/main/mapdrawgdal.c#L1555
> <https://eur06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FMapServer%2FMapServer%2Fblob%2Fmain%2Fmapdrawgdal.c%23L1555&data=05%7C01%7Cjukka.rahkonen%40maanmittauslaitos.fi%7C046212920572444ef6f008dad1504c07%7Cc4f8a63255804a1c92371d5a571b71fa%7C0%7C0%7C638052440048006207%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=eGNr6SWL6I0yQbse%2F5SAuV7QjISOBoyi30BxYB13C9Y%3D&reserved=0>
>
>
>
> It turns out that this small code change actually produces the desired
> behavior:
>
>        fScaledValue = (float) ((pafRawData[i]-dfScaleMin)*dfScaleRatio);
>
>         if( fScaledValue < 0.0 )
>
> -        pabyBuffer[i] = 0;
>
> +        if (pafRawData[i] > 0) {
>
> +            pabyBuffer[i] = 1;
>
> +        } else {
>
> +            pabyBuffer[i] = 0;
>
> +        }
>
> (I.e. if the original value was greater than 0, then assign 1 to this pixel such that it will be black and not transparent.)
>
> If this behavior can't yet be configured via mapscript, we could work on a pull request to implement this behavior, which would then be activated via a new configuration option.
> Do you have any thoughts on this? Does this make sense to you as a feature?
>
> Best regards,
> Bernhard
>
>
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