==== Modification of symbols - how to ====

**Where we may find the original definitions of symbols?**

On web pages
[[http://therion.speleo.sk/download.php|therion.speleo.sk/download.php]] is possible to download the source code of program Therion \\
(the *.tar.gz file.  Windows users might need to use something like 7-zip to extract these).

(An alternative method of obtaining the code is described on the [[metapost:|metapost page]])

After downloading and uncompressing find the folder **therion / mpost**.

In this folder you will find files thArea, thLine, thPoint, etc. Each file contains the definitions od symbols for particular group of them: thLine - line symbols, thArea - definitions of areas, thPoint - point symbols.

Each definition starts with keyword **def** and end with keyword **enddef;**
If we are looking for the definition of line symbol type slope we will find it in file **thLine** under name l_slope_SKBB where first character means group of symbol - in our example the **line**, next word means the type of symbol - **slope** and last group of characters is not important in this case - we may ignore it. The final name for our layout will be **l_slope**. we shoul copy all the code which is in the block **def - enddef**
     def a_slope_SKBB (.....)
       ....
       ....
     enddef

into layout section of thconfig between **code metapost** - **endcode** keywords. We change the name to **a_slope** and we may modify the necessary parameters. The best way to find the suitable value is to make several experiments.


**Example 1 - modification of array type debris**

In section of Metapost code we paste next code:

     def a_debris (expr p) =
     T:=identity;
     % thclean p;
     pickup PenC;
     path q; q = bbox p;
     picture tmp_pic;
     tmp_pic := image(
     for i = xpart llcorner q step 1u until xpart urcorner q:
       for j = ypart llcorner q step 1u until ypart urcorner q:
        draw ((-.2u,0)--(.2u,0))
        rotated uniformdeviate(360)
        shifted ((i,j) randomized 0.6u) withpen PenC;
       endfor;
     endfor;
    );
    clip tmp_pic to p;
    draw tmp_pic;
    enddef;

This code will generate the identical nonmodified symbol. We must modify the code first to modify the final symbol. 

We change 3 values in next lines:

     for i = xpart llcorner q step 1u until xpart urcorner q:
     for j = ypart llcorner q step 1u until ypart urcorner q:
     shifted ((i,j) randomized 0.6u) withpen PenC;

Value 1u and 06.u we cjange into:

     for i = xpart llcorner q step 0.7u until xpart urcorner q:
     for j = ypart llcorner q step 0.7u until ypart urcorner q:
     shifted ((i,j) randomized 0.4u) withpen PenC;

What we did? First two lines "say" to compiler that the symbols should be generated not as far from themselfs, third line "says" they should be more randomised.

Here is an exaple of modified  **layout** section in file **thconfig**.

      source homolak
      layout homolak
          #resolution of final map
          scale 1 100
          #color of final map.
          color map-bg 85 # dle barvy [100 100 100]
          #color by altitude
          #color map-fg altitude
          transparency on
          opacity 90
          # names of persons which surveyed the cave will be added how much they surveyed
          statistics topo-length on
          # the language of legends in map
          language cz
          #show the legend
          legend on
          map-header 8 100 e
          #type of used symbol sets SKBB/UIS/ASF/CCNP
          #symbol-set SKBB
          #to show the names of surveying points 
          debug station-names
          #setup of grid
          grid bottom
          grid-size 10 10 10 m
          #rotation of map
          #rotate 30
          #symbol-assign point station UIS
          #symbol-hide point station
          #don't generate any symbol
          #symbol-hide group all
          #don't generate point section symbol
          #symbol-hide point section
          #generate line wall symbol
          #symbol-show line wall
          #generate line survey symbol
          #symbol-show line survey
          #don't generate line flowstone symbol
          #symbol-hide line flowstone
     code metapost
     def a_debris (expr p) =
     T:=identity;
     % thclean p;
     pickup PenC;
     path q; q = bbox p;
     picture tmp_pic;
     tmp_pic := image(
     for i = xpart llcorner q step 1u until xpart urcorner q:
       for j = ypart llcorner q step 1u until ypart urcorner q:
        draw ((-.2u,0)--(.2u,0))
        rotated uniformdeviate(360)
        shifted ((i,j) randomized 0.6u) withpen PenC;
       endfor;
     endfor;
    );
    clip tmp_pic to p;
    draw tmp_pic;
    enddef;
    endcode
      endlayout
      export map -output output/homolak.pdf -layout homolak

**How it looks on map**

without modified Metapost code

{{:czsk:mmj:bez_layout.jpg|:czsk:mmj:bez_layout.jpg}}

with modified Metapost code

{{:czsk:mmj:layout.jpg|:czsk:mmj:layout.jpg}}

**Example 2 - modification of array type blocks**

We paste into Metapost code section next code:

      def a_blocks (expr p) =
      T:=identity;
      pickup PenC;
      path q, qq; q = bbox p;
      picture tmp_pic;
      uu := max(u, (xpart urcorner q - xpart llcorner q)/100, (ypart urcorner q - ypart llcorner q)/100);
      tmp_pic := image(
       for i = xpart llcorner q step 2.0uu until xpart urcorner q:
        for j = ypart llcorner q step 2.0uu until ypart urcorner q:
         qq := punked (((-.5uu,-.5uu)--(.5uu,-.5uu)--(.5uu,.5uu)--(-.5uu,.5uu)--cycle)
         randomized (uu/2))
         rotated uniformdeviate(360)
         shifted ((i,j) randomized 1.6uu);
         if xpart (p intersectiontimes qq) < 0:
          thclean qq;
          thdraw qq;
         fi;
        endfor;
       endfor;
     );
     clip tmp_pic to p;
     draw tmp_pic;
     enddef;

We will change following lines:

     for i = xpart llcorner q step 2.0uu until xpart urcorner q:
     for j = ypart llcorner q step 2.0uu until ypart urcorner q:
     shifted ((i,j) randomized 1.6uu);

We change values 2.0uu and 1.6uu to:

     for i = xpart llcorner q step 1.0uu until xpart urcorner q:
     for j = ypart llcorner q step 1.0uu until ypart urcorner q:
     shifted ((i,j) randomized 1.0uu);

What we did? As in first example first two lines "say" to compiler that the symbols should be generated not as far from themselfs, third line "says" they should be more randomised.

**Warning**

If the Therion generates an error in time of compilation you made the mistake in modification of code or you used too small values. Increase modified  values and try to generate map again. There could be a typo in modified definition - in that case erase the modified definition and paste the original definition into layout and make the modifications again.. 

**Final words**

I'll add another modified symbol definitions I made into this chapter..  

Don't hesitate and write into Therion conference if you have any question.

--- //[[fenrir@profisit.cz|Jan Balcařík]] 18/10/2006 12:29//