Easy Retopologising models preserving the fine-detail levels

by Ralf Klostermann (Rastaman), (www.rk-art.de)

First I refer to the Wiki:

http://www.zbrush.info/wiki/index.php/Rigging

http://www.zbrush.info/wiki/index.php/Topology

and my Tutorials about the yet undocumented feature of Zsphere-topology-based modelling and rigging and the hidden secrets in topology and rigging :

http://www.zbrushcentral.com/zbc/showthread.php?t=46117

and of course Plakkie's marvelous thread which started all:

http:// www.zbrushcentral.com /zbc/showthread.php?t=44876&page=1&pp=15

Why should you retopologise your models ?

There are several reasons why you should think about 'retopoing' your existing models.Maybe you already have created a very good model, but some areas doesn't render cleanly because of a bad topology there. Simply retopo your model and fix the bad areas.

On the other hand, the availability of the retopology-feature gives you less stress when you sculpt your models. Just follow your imagination, create how you like without always having the flow of your polygon-connection-lines in mind.When you're happy with the shape you created, simply reotopo the model and you will have a clean mesh.

So far, so good.But as simple as it sounds, you will soon discover that it is by far not so easy.

The major problem beside the handwork is that you will loose the details of theoriginal mesh. But the soulution for that is already described in the Wiki under the topic:

'1.3 Importing Topology From Outside of ZBrush'But I must say, I did read it but I simply did not realize a long time what it really meant.So I decided to make this short tutorial to give a clear step-by step how to use this principle with retopoed meshes.

Some notes

On Plakkies 'Topology and Flowlab' - Mainpage (look above for the link) you will find several ways of setting up your mesh for retopo-work.

This Tutorial describes my personal workflow what does not mean that it is the absolute best or only way. But it works very fine for me.;)

This technique uses the original-mesh in the most low-poly-status as possible.You can also go this way with higher-poly meshes, but avoid the quick-retopo-method with Shift-draw, because ZBrush can't handle such data amount and will crash.

So here we go ;)

First we retopologize our original Mesh that has some faults:

● Bring your original-mesh (or a copy of it) to the lowest subdivision-level (Subd-level 1).

● Make a copy of your original mesh. (not really needed, just for safety reason).

● Choose a zsphere as active tool, draw it on the canvas and press Edit and Draw.

● Go to Tool -> Rigging -> Select and select your original-mesh or the copy.

● Open Tool -> Topology and press Edit Topology.

● Ctrl + LMB-Click on any point you want to start from. (If you don't do so, the first drawn point will be connected to the big ZSphere you choosed as tool.

(Note: If you want to see the detailed high-poly-Version of your model laying underneath a low-poly Topo-mesh, you'll have to set up your mesh in another way.That is descriped on Plakkies 'Topology and Flowlab'-Mainpage:

Editing existing topology

1. Load the model you want to edit 2. Select a new ZSphere tool. 3. Clone your model. 4. Make sure that the subdiv level of the cloned model is at 1 or 2 (If you don't, it

doesn't work! The original model can have as high subdiv levels as you like) 5. In the Tool:Rigging subpalette, select the original model, and activate (optional) the

Projection Mode, so that the model which will be generated is projected on the Template.

6. In the Tool:Topology subpalette, select the cloned model. All the lines will show up. 7. Enter the Edit Topology Mode.

)

Now you can paint the new mesh either by free hand or better via the Quick-Retopo-Technique (first described by 'Crusoe the Painter').

For the quick and easy way, start with Ctrl + LMB-Click on any place of the

model, then use Shift + LMB-hold to paint quickly over the model:

● Be sure to be in Edit- and Draw-mode.

● Place your mouse-pointer over the mesh, press and hold Shift and press and hold left mouse-button while you paint quickly over the mesh.While doing this, parts of the mesh will highlighten in orange what indicates that you just created a new topology over the old mesh.

Note: This quick-topo-way does only work good with low-poly-versions of your meshes. Don't try this with high-polys, ZB3 will crash for sure !

● To check your created new topology, rotate your view a little bit an you will see it clearly. (Rotation of the view is needed to update the view, otherwise you won't see your new topo-mesh)

● Fix unclean areas by erasing the quick-produced topology (Alt + LMB-Click on a Topo-Point, for disconnecting lines first Ctrl + LMB-Click -> LMB-Click on that line to insert a new point, then erase him again) and redo the topology-structure there by free-hand-work.

Mesh with faults Fixed mesh with clean topology

● Press 'a' to preview and check the surface for for holes.Press 'a' again and redo the steps above to create a clean topology.

Notes:

➔ When you go again with Shift + LMB over topologized areas, the topology will be erased. No problem, repead it frequently starting again from an untopologized area and move fast. With some training, you will be soon able to create a clean topology by this way.

➔ If you saved your Model in this topology-creating-status and reload it later and you cannot edit the topology, go to Tools -> Toplogy and unpress Edit Toplogy, then press it again to reactivate the Edit-Topology-mode.You should now be able again to modify your topology.

➔ If you cannot move or delete a topo-point, you have masked areas.Ctrl + LMB-Drag a rectangle on a free part of the canvas to unmask all and try again.

● If you want your retopoed mesh in Subd-level 1 , make sure that the sliders of the topology-panel and especially in the adaptive skin-panel are like shown here to create again a new low-poly mesh.

● When you are done, press Tool -> Adaptive Skin -> Make Adaptive Skin to produce your final retopologized mesh. Save it as .ztl or .obj.

Note: By saving as .ztl you ensure that the saved retopoed mesh will remain in the same size as the original mesh. If you save as .obj, the you will mostly have to resize the mesh later again to match the original before you can proceed the detail-transfer. So I strongly recommend to always save it as .ztl.

Now to our main problem, the recovering of the lost details in your new created topo-mesh. The way is according to the description in the Wiki under '1.3 Importing Topology From Outside of ZBrush'

● Load or import your retopologized Mesh (it has so far only one low-poly-level with the base-structure but without any details).

● Choose your original model as active tool, draw it on the canvas and press Edit.

● Be sure to be in Draw-Mode.

● Now bring your original mesh to the highest subd-Level.

● For all cases, in this highest Subd-Level save a MorphTarget (Tool-Palette). With that, you can later reveal all details that doesn't come up with the main detail-transfer manually by using the usual Morph-sliders or the new ZB3 Morph-Brush (see Wiki)

● Choose a zsphere as active tool

● Go to Tool -> Rigging -> Select and choose your original mesh (that is in its highest subd-level showing all the fine details)

● Now go to Tool -> Topology -> Select and choose your low-poly retopoed mesh. Then press 'Edit Topology' and decrease the Topology -> Subdiv-Level from the default level (2) to Level 1. With that ZBrush will later calculate the subd-levels of the final mesh on the base of subd-level 1.

● Now activate Tool -> Rigging -> Projection.This will project all the fine details from the original high-poly-mesh to the low-poly retopoed mesh

● Now go to Tool -> Adaptive skin and set Density to a higher value (how high depends on the fineness of the details you want to transfer, so try and adjust as needed). Try at least the same value as the number of subd-levels your final mesh should have.Then press 'a' to preview your new mesh.

Depending on the Adaptive-Skin-Density-level you choosed it may take some seconds for ZBrush to calculate the new mesh.

● You can now fine-tune the result with the sliders in the Adaptive-Skin-Tab (Density, IRes,Mbr) until you are satisfied with the result.

● Then press 'Make Adaptive Skin'.

This produces the final mesh. Select it as the active Tool.Now go up your subd-levels and enjoy your detailed model with a new clean and fixed base topology.

The retopologized mesh with projected fine details:

Happy ZBrushing,

Ralf

Appendix

If you are running into a scale-problem by performing the setup for the detail-transfer, meaning that your loaded or reimported low-poly-retopoed mesh is a lot smaller than your high-poly original-mesh after you had select it in the Topology -> Select-dialogue, you should check this to fix it:

✔ Before you store your freshly created low-poly-mesh after the basic-retopo-procedure (immediately after you made it Adaptive skin) , use the Tool -> 'Make Polymesh 3D' Button and then save and use this now created copy instead of the Adaptive Skin-Version for the detail-transfer.

The Make Polymesh 3D-step saves the mesh in the right scale.

Thanks to Nickz for this very usefull hint ;)

If this does not work, try this:

✔ Be sure that you have turned off any transpose translation/scaling - line.Therefore go within your original model into move,scale or rotate-mode and LMB-Click once on any point of your mesh.The transpose-line should now disappear.Now do your retopo-work.When you created the retopoed low-polymesh, check this again for that mesh before you store it as .ztl or export it as an object.

✔ Use the retopoed low-poly-mesh directly without first saving and reloading it.If any transpose line is turned off before you do any retopo-work, you should have exactly the same scaling between the original-mesh and the low-poly-retopo-mesh.

And a further hint at the end:

Remember to use the morph-sliders and / ore the new Morph-Brush to reveal all details that didn't come up with the initial detail-transfer-process.

Using the Morph-Brush to reveal all extra-fine-details:

This tool is used after you have created your final step and have your detailed 4-level retopoed-model.

To make use of this tool you must have stored previously a Morph-target when your original high-poly-mesh was in its highest subd-level (just before you entered the setup for the fine-detail-transfer).

If you stored that Morph-target, it is now also contained in your new 4-level retopoed model.

Now activate the Morph-Brush, turn on Draw, turn off all other Buttons in the top-row except ZSub, set the Z-intensity-slider to a medium level of 30-50 and begin to draw over your mesh where you miss previous existed details.

But be carefull not to overmodel, what easily occurs when you set a too high z-intensity.

By switching to ZAdd and drawing you can undo the revealing.

With a little training you will have nearly perfect results. ;)

Furthermore, a common hint for all who get wired results when previewing the projected topo-mesh in adaptive skin preview:

1)Begin your attempt with a low Density-value in the Tool -> Adaptive Skin -> Density setting.Try a first time with a level of 2.If it looks right, increase this value step by step (3 then 4) and always press 'a' to preview your results.From some density-level on (depending on the polygon-count of your retopoed low-poly-mesh), ZB3's algorhythms will fail to produce a clean result.So that will be your individual adaptive-skin-density-limit you cannot overcome.

2)Second, the Tool -> Rigging -> projection-strength-value might be to high.Lower the value in that case below 1 and try again.

Important change in this new tutorial-version:

A big credit to nRatio for giving me an essential hint about a fault I made in the previous versions of this tutorial.

As you already might have noticed above, I changed the advice for the Rigging -> subdiv-Level-setting from 4 to 1.

The Topology -> subdiv-slider must be set to 1, then you will get the same subd-level-amount as what is set in the Adaptive-skin -> Density-slider-value, but only if there was no previous adaptive-skin-preview etc. with any higher setting of the subdiv-slider !

If there was, you have to exit the setup and rebuild it totally new.

So the very first thing you should do after loading both meshes in the rigging- and topology-slots is to set the topology -> subdiv-slider from 2 down to 1.