We describe a pseudo-3D photoionization code , NEBU_3D and its associated visualization tool , VIS_NEB3D , which are able to easily and rapidly treat a wide variety of nebular geometries , by combining models obtained with a 1D photoionization code .
The only requirement for the code to work is that the ionization source is unique and not extended .
It is applicable as long as the diffuse ionizing radiation field is not dominant and strongly inhomogeneous .
As examples of the capabilities of these new tools , we consider two very different theoretical cases .
One is that of a high excitation planetary nebula that has an ellipsoidal shape with two polar density knots .
The other one is that of a blister HII region , for which we have also constructed a spherical model ( the spherical impostor ) which has exactly the same H \beta surface brightness distribution as the blister model and the same ionizing star .

We present and comment line intensity maps corresponding to different viewing angles .
We also use the computed line intensities to derive physical properties of the model in the same way as an observer would do for a real object .
For example , we derive the “ apparent ” value of N/O for the entire nebulae and along spectral slits of different orientations .
For this we take the electron temperature and density derived from the [ N ii ] 5755Å/ [ N ii ] 6583Å and [ O ii ] 3726Å/ [ O ii ] 3729Å ratios , respectively , and we adopt the common recipe : N/O=N ^ { + } /O ^ { + } .
Interestingly , we find that , in the case of our high excitation nebula , the derived N/O is within 10-20 % of the real value , even when the slit crosses the high density knots .
On the other hand , for the blister HII region and its spherical impostor , we find that the apparent N/O is much smaller than the true one ( about 0.68 and 0.5 of it , respectively ) .

These two examples warn against preconceived ideas when interpreting spectroscopic and imaging data of HII regions and planetary nebulae .
The tools NEBU_3D and VIS_NEB3D , which will be made publicly available in the future , should facilitate the performance of numerical experiments , to yield a better understanding of the physics of aspherical ionized nebulae .