[mapserver-dev] RFC-86: scale dependant DATA substitutions

[Stephen Woodbridge]

Thomas,

OK, got it, but this is not intuitive because one has to do math to 
figure out where the breaks will happen. And it is even harder to figure 
out what numbers I should use if a want a break at X scale, because the 
number I use in the VALUES affects BOTH the scale above and below the 
number I change. This also does not follow how the usage of 
MINSCALEDENOM/MAXSCALEDENOM in the rest of the mapfile.

I think you have to make the ranges explicit and break on the scale 
numbers not between them. This means you have to have an extra case in 
the values like I suggested, which you were probably trying to avoid.

I think it would be a good idea to get additional input from others on 
this. I suspect other users will be just as confused but the proposed 
scheme as I was.

Thanks,
   -Steve W

On 10/8/2012 2:08 PM, thomas bonfort wrote:
> Steve,
>
> starting from
>
> VALUES
>        "1000" "1000"
>        "10000" "10000"
>        "1000000" "1000000"
> END
>
> let's change this to:
>
> VALUES
>        "1000" "foo"
>        "10000" "bar"
>        "1000000" "baz"
> END
>
> to avoid confusion between keys and values. Now, this should be read as:
> - for scale 1000, use "foo"
> - for scale 10000, use "bar"
> - for scale 1000000, use "baz"
>
> at rendering time, with a current map scale "s", find which is the
> closest configured scale to s,
> i.e.:
>
> - if s < 1000 use "foo"
> - else if 1000<s<10000: if s closer to 1000 than 10000 use "foo", else
> use "bar". i.e. the test for s<5500
> - etc...
>
> wrapping it all up you get:
>
> 0 ... foo ... 5500 ... bar ... 505000 ... baz ....
>
> hope this clarifies things :)
>
> --
> thomas
>
> On Mon, Oct 8, 2012 at 7:51 PM, Stephen Woodbridge
> <woodbri at swoodbridge.com> wrote:
>> On 10/8/2012 11:32 AM, thomas bonfort wrote:
>>>
>>> On Mon, Oct 8, 2012 at 4:41 PM, Stephen Woodbridge
>>> <woodbri at swoodbridge.com> wrote:
>>>>
>>>> On 10/8/2012 9:02 AM, thomas bonfort wrote:
>>>>>
>>>>>
>>>>> Devs,
>>>>>
>>>>> Please take a look and comment on
>>>>>
>>>>> http://mapserver.org/trunk/development/rfc/ms-rfc-86.html
>>>>
>>>>
>>>>
>>>> Hi Thomas,
>>>>
>>>> Thanks, this looks like an excellent implementation to address the need I
>>>> identified in bug #3150.
>>>>
>>>> I'm a little confused with your first example in the RFC, you have:
>>>>
>>>>     SCALETOKEN
>>>>       NAME "foobar"
>>>>       VALUES
>>>>         "1000" "1000"
>>>>         "10000" "10000"
>>>>         "1000000" "1000000"
>>>>       END
>>>>     END
>>>>
>>>> But the discussion reference 5500, 505000. So that should be cleared up
>>>> so
>>>> it is more understandable.
>>>
>>> Steve,
>>> what this meant is that given the current requested scale, mapserver
>>> will select the closest defined scaletoken. In the example here,
>>> 0=>5500 uses the 1000 value
>>> 5500=>505000 uses 10000
>>> 505000 and up uses 1000000
>>>
>>> I agree, not very clear... you should only consider the first entry,
>>> the second one isn't interpreted and is just used as the replacement
>>> for the token
>>
>>
>> My confusion is how to determine the ranges. For example, if:
>>
>>        0 < scale <=   1000 use    1000
>>     1000 < scale <=  10000 use   10000
>> 1000000 < scale           use 1000000
>>            scale > 1000000 use      ??
>>
>> So, you define three points in the scale range (ie: 1000, 10000, 1000000) so
>> it is not clear what happens above or below these points, especially above
>> and below the top and bottom ones. If this is better defined, then maybe
>> there is no need for a default case.
>>
>> You might do something like:
>>
>>
>> VALUES
>>       "1000"    "1000"
>>      "10000"   "10000"
>>     "100000"  "100000"
>>    ">100000" "1000000"
>> END
>>
>> So this would interpret the first column as the maxscaledenom to apply the
>> token to, with the last one being the default case. I would consider
>> removing the number after ">" to make it less ambiguous if someone edited
>> the mapfile and you had something like:
>>
>>
>> VALUES
>>       "1000"    "1000"
>>      "10000"   "10000"
>>     "100000"  "100000"
>>     "200000"  "200000"  # added this line
>>    ">100000" "1000000"  # this is confusing at best, conflicts w "200000"
>>          ">" "1000000"  # this is more clear and does not depend
>>                         # on the user editing two lines
>> END
>>
>> Do the scales need to be in ascending or descending order or will you sort
>> them if they need to be ordered.
>>
>> Then again, I might be over thinking this.
>>
>> Thanks,
>>    -Steve